Biological evolution

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**Biological developments**
Philogenetic-sybiogenetic tree of living beings
Key topics
Introduction to evolution Common ancestor Scientific theory Scientific evidence
Processes and consequences
Genetics of populations Variation Diversity Mutation Natural selection Adaptation Philogenia Polimorphism Genetic derogation Genetic flow Spice Adaptive radiation Cooperation Coevolution Parallel developments Extinction Transitional form LUCA
History
Abiogenesis History of life History of evolution Criticism of evolutionary theory Charles Darwin The Origin of Species Human evolution Molecular evolution
Fields and applications
Applications of evolution Evolutionary aesthetic Evolutionary Computation Evolutionary Ecology Evolutionary Ethics Evolutionary Theory of Games Evolutionary Linguistic Evolutionary Medicine Evolutionary Neuroscience Evolutionary Physiology Evolutionary psychology Pilot developments

Evolution as a proven fact

Evolution is as much a "fact" (an observation, measurement, or other form of evidence) as a "theory" (a comprehensive explanation of some aspect of nature that is supported by a large body of evidence). The National Academies of Sciences, Engineering, and Medicine states that the theory of evolution is "a scientific explanation that has been tested and confirmed so many times that there is no compelling reason to continue. trying it out or looking for additional examples".

Evidence of the evolutionary process

Evidence for the evolutionary process comes from the body of evidence scientists have assembled to show that evolution is a process characteristic of living matter and that all organisms living on Earth descend from a universal last common ancestor. Existing species are a stage in the evolutionary process, and their relative richness and levels of biological complexity are the product of a long series of speciation and extinction events.

The existence of a common ancestor can be deduced from a few simple characteristics of the organisms. First, there is evidence from biogeography: both Charles Darwin and Alfred Russell Wallace realized that the geographic distribution of different species depends on the distance and isolation of the areas they occupy, and not on similar ecological and climatic conditions, as would be the case. to be expected if the species had appeared at the same time already adapted to their environment. Later, the discovery of plate tectonics was very important for the theory of evolution, providing an explanation for the similarities between many groups of species on continents that were united in the past. Second, the diversity of life on the Earth does not resolve into a completely unique set of organisms, but rather they share a great number of morphological similarities. Thus, when the organs of different living beings are compared, similarities are found in their constitution that indicate the relationship that exists between different species. These similarities and their origin allow organs to be classified into homologues, if they have the same embryonic and evolutionary origin, and analogous, if they have a different embryonic and evolutionary origin, but the same function. Anatomical studies have found homology in many structures superficially so different, such as the spines of cacti and the traps of various insectivorous plants, indicating that they are simply leaves that have undergone adaptive modifications. Evolutionary processes also explain the presence of vestigial organs, which they are reduced and have no apparent function, but clearly show that they are derived from functional organs present in other species, such as the rudimentary hind leg bones present in some snakes.

Embryology, through comparative studies of the embryonic stages of different kinds of animals, offers another set of clues to the evolutionary process. It has been found that in these early stages of development, many organisms show common features that suggest the existence of a shared development pattern between them, which, in turn, suggests the existence of a common ancestor. The fact that early embryos of vertebrates such as mammals and birds have gill slits, which then disappear as development progresses, can be explained by their being related to fish.

Another set of clues comes from the field of systematics. Organisms can be classified using the above similarities into hierarchically nested groups, much like a family tree. While modern research suggests that due to horizontal gene transfer, this tree of life may be more complicated than expected. than previously thought, as many genes have been distributed independently among distantly related species.

Species that have lived in ancient times have left records of their evolutionary history. Fossils, together with the comparative anatomy of current organisms, constitute the paleontological evidence of the evolutionary process. By comparing the anatomies of modern species with those already extinct, paleontologists can infer the lineages to which one and the other belong. However, paleontological research to search for evolutionary connections has certain limitations. In fact, it is useful only in those organisms that have hard body parts, such as shells, teeth, or bones. Furthermore, certain other organisms, such as prokaryotes -bacteria and archaea- have a limited number of common characteristics, so their fossils do not provide information about their ancestors.

A more recent method of proving the evolutionary process is the study of biochemical similarities between organisms. For example, all cells use the same basic set of nucleotides and amino acids. The development of molecular genetics has revealed that the evolutionary record resides in the genome of each organism and that it is possible to date the time of species divergence to through the molecular clock based on mutations accumulated in the process of molecular evolution. For example, the comparison between human and chimpanzee DNA sequences has confirmed the close similarity between the two species and has helped to elucidate when the ancestor existed common to both.

The origin of life

Main article: Abiogenesis

The origin of life, although it concerns the study of living beings, is a subject that is not addressed by the theory of evolution; since the latter only deals with the change in living beings, and not with the origin, changes and interactions of the organic molecules from which they come.

Not much is known about the earliest and pre-developmental stages of life, and attempts to unravel the earliest history of the origin of life generally focus on the behavior of macromolecules, because the current scientific consensus is that the complex biochemistry that makes up life arose from simple chemical reactions, although controversy remains about how these occurred. However, scientists agree that all existing organisms share certain characteristics ― including the presence of cell structure and genetic code― that would be related to the origin of life.

It is also unclear what were the first developments of life (protobionts), the structure of the first living things, or the identity and nature of the last universal common ancestor. Bacteria and archaea, the first organisms to leave a trace in the fossil record, they are too complex to have arisen directly from non-living materials. The lack of geochemical or fossil clues to earlier organisms has left a wide field for hypotheses. Although there is no scientific consensus on how life began, the existence of the last universal common ancestor is accepted because it would be virtually impossible that two or more separate lineages could have independently evolved the many complex biochemical mechanisms common to all living organisms.

It has been proposed that the start of life may have been self-replicating molecules such as RNA, or assemblies of simple cells called nanocells. Scientists have suggested that life arose in deep-sea hydrothermal vents, geysers, or fumaroles during the Hadic. An alternative hypothesis is that of the beginning of life in other parts of the Universe, from where it would have reached Earth in comets or meteorites, in the process called panspermia.

The evolution of life on Earth

Philogenetic tree showing the divergence of the modern species of its common ancestor in the center. The three domains are coloured as follows; the bacteria in blue, the arches in blue and the eukaryotes in green.

Main article: History of life

Detailed chemical studies based on carbon isotopes of Archean rocks suggest that the first forms of life emerged on Earth probably more than 4.35 billion years ago, at the end of the Hadic eon, and there are clear geochemical clues ―such as the presence in ancient rocks of sulfur isotopes produced by the microbial reduction of sulfates—indicating their presence in the Paleoarchic era, three thousand four hundred and seventy million years ago. Stromatolites—layers of rock produced by communities of microorganisms—older they are recognized in 3.7 billion-year-old strata, while the oldest threadlike microfossils are found in semi-mentary rocks from 3.77–4.28 billion-year-old hydrothermal vents found in Canada.

Furthermore, molecular fossils derived from the lipids of the plasma membrane and the rest of the cell – called 'biomarkers' – confirm that certain cyanobacteria-like organisms inhabited the archean oceans more than 2.7 billion years ago. These photoautotrophic microbes released oxygen, which began to accumulate in the atmosphere approximately 2.2 billion years ago and permanently transformed its composition. The emergence of an oxygen-rich atmosphere following the rise of photosynthetic organisms can also be traced by layered deposits of iron and the red bands of later iron oxides. The abundance of oxygen enabled the development of aerobic cellular respiration, which emerged approximately 2 billion years ago.

From the formation of these first complex life forms, the prokaryotes, 4.25 billion years ago, billions of years passed without any significant change in cellular morphology or organization in these organisms, until the advent of eukaryotes from the integration of an archaea of the Asgard clade and an alphaproteobacteria forming a cooperative association called endosymbiosis. Eukaryotes are cladistically considered one more clade within the archaea. Bacteria incorporated into archaean host cells, initiated a process of coevolution, by which bacteria gave rise to mitochondria or hydrogenosomes in eukaryotes. It is also postulated that a giant poxvirus-like DNA virus gave rise to the nucleus of eukaryotic cells by having the virus incorporated into the cell where instead to replicate and destroy the host cell, it would remain inside the cell, later giving rise to the nucleus and giving birth gar to other genomic innovations. This theory is known as 'viral eukaryogenesis'. Both molecular and paleontological evidence indicates that the first eukaryotic cells arose around 2.5 billion years ago.

A second independent event of endosymbiosis occurred 2.1-1.9 billion years ago which led to the formation of chloroplasts from cyanobacteria and a protozoan which would give rise to red algae and green algae, later to algae. Green plants that managed to leave the aquatic environment evolved during the Cambrian. On the other hand, other algae such as diatoms or brown algae obtained their chloroplasts by secondary endosymbiosis between protozoa with red or green algae, but evolutionarily they are not related to red or green algae.

Multicellular life arose from the colonial union of microorganisms to manage to form fruitful organs, tissues and bodies. According to molecular and structural analyses, the animals originated from a colonial union of protozoa similar to choanophlegellae forming crowns of microvilli and with a tendency to cellular specialization, choanoflagellates are protozoa similar to animal spermatozoa and choanocyte-like cells. presented by some animals that are genetically the closest protists to animals. The fungi evolved from amoeboid parasitic protozoa that, due to their parasitism, lost phagocytosis, being replaced by osmosis and had a tendency to form filamentous colonies. Fungi and animals are the kingdoms of nature that are genetically closest to each other and are grouped together in the Opisthokonta clade along with their closest protozoa. In addition, its cells are uniflagellate and opisthoconta similar to spermatozoa. Although more evolved fungi such as mushrooms or molds lack flagella in their cells, this is preserved in more primitive fungi such as chytrids or microsporidia, so fungi evolved from ancestors similar to those of animals. Slime molds could be a better model of how one can transition from unicellular to multicellular life, since certain plasmodial amoebas can group together in colonies and form a fruiting body capable of sliding across the ground. On the other hand, myxobacteria when grouped together in colonies can form small fruiting bodies like amoebas, thus this shows that multicellularity can be gained not only in eukaryotes, but also in prokaryotes.

The oldest fossils that would be considered eukaryotes correspond to the 2.1 billion-year-old biota of France, which were probably slime molds that would represent the first indications of multicellular life. The organisms measured around 12 cm and consisted of flat disks with a characteristic morphology and included circular and elongated individuals. In certain aspects they are similar to some organisms of the Ediacaran Biota. In addition, according to scientific studies, they could have a multicellular life state and a unicellular one, since they would develop from cellular aggregates capable of forming plasmodial fruiting bodies.

The history of life on Earth was that of single-celled eukaryotes, bacteria, and archaea until about 580 million years ago, when the first multicellular organisms appeared in the oceans in the Ediacaran period. These organisms are known as the Biota of the Ediacaran period.

It is possible that some Ediacaran organisms were closely related to groups that predominated later, such as porifera or cnidarians. However, due to the difficulty in deducing evolutionary relationships in these organisms, some paleontologists have suggested that the Ediacaran biota represents a completely extinct branch, a "failed experiment" of multicellular life, and that later multicellular life later re-evolved from unrelated unicellular organisms. In any case, the evolution of organisms Multicellular microorganisms occurred in multiple independent events, in organisms as diverse as sponges, brown algae, cyanobacteria, slime fungi, and myxobacteria.

Shortly after the appearance of the first multicellular organisms, a great diversity of life forms appeared in a period of ten million years, in an event called the Cambrian explosion, a brief period in geological terms, but one that implied a diversification animal with no parallel documented in fossils found in the sediments of the Burgess Shale, Canada. During this period, most of today's animal phyla appeared in the fossil record, as well as a large number of unique lineages that subsequently became extinct. Most modern animal body plans originated during this period.

Possible triggers for the Cambrian Explosion include the buildup of oxygen in the atmosphere due to photosynthesis.

Approximately 500 million years ago, plants and fungi colonized the land and were quickly followed by arthropods and other animals.

Amphibians appeared in Earth's history about 300 million years ago, followed by the first amniotes, then mammals about 200 million years ago, and birds about 150 million years ago. However, microscopic organisms, similar to those that evolved early, continue to be the predominant form of life on Earth, as most species and terrestrial biomass are made up of prokaryotes.

History of evolutionary thought

Main article: History of evolutionary thought

Infographic that summarizes the history of evolutionary thought.

Anaximandro, a Greek philosopher, offered a more elaborate idea and maintained that "the basis of all matter is an eternal substance that is transformed into all commonly known material forms. These forms, in turn, change and melt into others according to the rule of justice, that is, a kind of balance and proportion."

Aristotle, classified the animals according to a "natural cod".

Several ancient Greek philosophers contemplated the possibility of changes in living organisms over time. Anaximander (ca. 610-546 BCE) suggested that the first animals lived in water and gave rise to land animals. Empedocles (ca. 490-430 BCE) wrote that the first living things came from of the earth and species arose through natural processes without an organizer or final cause. Such proposals survived until Roman times. The poet and philosopher Lucretius, followed Empedocles in his masterpiece De rerum natura (On the nature of things) where the universe works through naturalistic mechanisms, without any supernatural intervention. If the mechanistic vision is found in these philosophers, the teleological vision occurs in Heraclitus, who conceives the process as a rational development, in accordance with the Logos. Development, as well as the process of becoming, in general, was denied by the Eleatic philosophers.

The works of Aristotle (384-322 BC), the first naturalist whose work has been preserved in detail, contain very astute observations and interpretations, albeit mixed with various myths and errors that reflect the state of knowledge in his time; his effort is notable in exposing the existing relationships between living beings as a scala naturae ―as described in Historia animalium― in which organisms are They are classified according to a hierarchical structure, "ladder of life" or "chain of Being", ordered according to the complexity of their structures and functions, with organisms that show greater vitality and capacity for movement described as "higher organisms". In contrast to these materialist views, Aristotelianism viewed all natural things as actualizations of fixed natural possibilities, known as forms. This was part of a teleological understanding of nature in which all All things have a role they are destined to play in a divine cosmic order. The entire transition from potentiality to actuality (fromdynamis to entelecheia) is nothing more than a transition from the lower to the higher, to the perfect, to the Divine. Aristotle criticized Empedocles' materialistic theory of evolution, in which random accidents could lead to orderly outcomes, however he did not argue that species cannot change or become extinct, and accepted that new types of animals can occur in very rare cases.

The Stoics followed Heraclitus and Aristotle in the main lines of their physics. With them, the whole process is carried out according to the purposes of the Divine. Variations of this idea became the standard understanding of the Middle Ages and were integrated into Christianity. Saint Augustine takes an evolutionary view as his basis. for his philosophy of history. Erigena and some of her followers seem to teach a kind of evolution. Thomas Aquinas did not detect any conflict in a divinely created universe and developed over time through natural mechanisms, arguing that the autonomy of nature was a sign of God (Fifth Way).

Some ancient Chinese thinkers also expressed the idea that biological species change. Zhuangzi, a Taoist philosopher who lived around the 4th century B.C. C., mentioned that life forms have an innate ability or power (hua 化) to transform and adapt to their environment.

According to Joseph Needham, Taoism explicitly denies the immutability of biological species and Taoist philosophers speculated that they developed different attributes in response to different environments. In fact, Taoism refers to humans, nature, and the sky as existing in a state of "constant transformation", in contrast to the more static view of nature typical of Western thought.

Portrait of Jean-Baptiste Lamarck

Alfred Russel Wallace in 1895

While the idea of biological evolution has been around since ancient times and in different cultures — for example, it was first outlined in Muslim society in the 19th century IX Al-Jahiz and in the XIII Nasir al-Din al-Tusi century respectively—, The modern theory was not established until the 18th and 19th centuries, with contributions from scientists such as Christian Pander, Jean-Baptiste Lamarck, and Charles Darwin.

In the 17th century, the new method of modern science rejected the Aristotelian approach, the idea of final causes. He sought explanations of natural phenomena in terms of physical laws that were the same for all visible things and that did not require the existence of any fixed natural category or cosmic divine order. In biology, however, teleology persisted for longer, that is, the view according to which there are ends in nature. This new approach was slow to take root in the biological sciences, the last bastion of the concept of fixed natural types. John Ray applied one of the previously most general terms for fixed natural types, "species", to the types of plants and animals, but he strictly identified each type of living thing as a species and proposed that each species could be defined by characteristics that perpetuated themselves generation after generation. The biological classification introduced by Charles Linnaeus in 1735 explicitly recognized the hierarchical nature of relationships between species, but still regarded species as fixed according to a divine plan.

In the 18th century, the opposition between fixism and transformism was ambiguous. Some authors, for example, admitted the transformation of species at the genus level, but denied the possibility that they changed from one genus to another. Other naturalists spoke of "progression" in organic nature, but it is very difficult to determine if with this they were referring to a real transformation of the species or it was simply a modulation of the classical idea of scala naturae< /i>. Among the German philosophers, Herder established the doctrine of a continuous development in the unity of nature, from the inorganic to the organic, from the stone to the plant, from the plant to the animal and from the animal to man. Kant is also often mentioned as one of the first teachers of the modern theory of descent.

Georges-Louis Leclerc de Buffon (1707-1788) suggested that species could degenerate into different organisms, and Erasmus Darwin (1731-1802) proposed that all warm-blooded animals could have descended from a single microorganism (or & #34;filament").

Jean-Baptiste Lamarck (1744-1829) formulated the first theory of evolution or "transmutation" and proposed that organisms, in all their variety, had evolved from simple forms created by God and He postulated that those responsible for this evolution had been the organisms themselves due to their ability to adapt to the environment: changes in that environment generated new needs in the organisms and these new needs would entail a modification of them that would be heritable. He relied for the formulation of his theory on the existence of remains of extinct intermediate forms. With this theory, Lamarck faced the general belief that all species had been created and remained unchanged since their creation and also opposed the influential Georges Cuvier (1769-1832) who justified the disappearance of species not because they were intermediate forms between the original and the current ones, but because they were different forms of life, extinguished in the different geological cataclysms suffered by the Earth. While Thus, the ideas of John Ray and of benevolent design had been developed by William Paley in Natural Theology (1802), who proposed complex adaptations as evidence of divine design and who was admired by Charles Darwin.

Cover The Origin of Species

It was not until the publication of Charles Darwin's On the Origin of Species that the fact of evolution began to be widely accepted. A letter from Alfred Russel Wallace, in which he revealed his own discovery of natural selection, prompted Darwin to publish his work on evolution. Therefore, both are sometimes given credit for the theory of evolution, also calling it the Darwin-Wallace theory.

A particularly interesting debate in the evolutionary field was held by the French naturalists Georges Cuvier and Étienne Geoffroy Saint-Hilaire in the year 1830. Both disagreed on the fundamental criteria to describe the relationships between living beings; while Cuvier relied on functional anatomical features, Geoffroy gave more importance to morphology. The distinction between function and form led to the development of two fields of research, known respectively as functional anatomy and transcendental anatomy. Thanks to the work of the British anatomist Richard Owen, the two views began to be reconciled, a process completed in Darwin's theory of evolution.

Although Darwin's theory profoundly shook scientific opinion regarding the development of life, even having social influences, it could not explain the source of variation between species, and furthermore Darwin's proposal of the The existence of a hereditary mechanism (pangenesis) did not satisfy most biologists. It was not until the late 19th century and early 20th century that these mechanisms could be established.

When around 1900 the work of Gregor Mendel at the end of the 19th century on the On the nature of heredity, a dispute ensued between the Mendelians (Charles Benedict Davenport) and the biometricians (Walter Frank Raphael Weldon and Karl Pearson), who insisted that most of the pathways important to evolution must show continuous variation that does not exist. It was explainable through Mendelian analysis. Eventually the two models were reconciled and merged, primarily through the work of biologist and statistician Ronald Fisher. This combined approach, which applied a rigorous statistical model to Mendel's theories of inheritance via genes, became known in the 1930s and 1940s and is known as the synthetic theory of evolution.

In the 1940s, following Griffith's experiment, Avery, MacLeod, and McCarty were able to definitively identify deoxyribonucleic acid (DNA) as the "transforming principle" responsible for the transmission of genetic information. In 1953, Francis Crick and James Watson published their famous work on the structure of DNA, based on the research of Rosalind Franklin and Maurice Wilkins. These advances ushered in the era of molecular biology and led to the interpretation of evolution as a molecular process.^{[citation needed]}

In the mid-1970s, Motoo Kimura formulated the neutralist theory of molecular evolution, firmly establishing the importance of genetic drift as the primary mechanism of evolution. To date, debates continue in this area of research. One of the most important is about the theory of punctuated equilibrium, a theory proposed by Niles Eldredge and Stephen Jay Gould to explain the paucity of transitional forms between species.

Darwinism

Main article: Darwinism

Charles Darwin, father of the theory of evolution by natural selection.
Photograph by Julia Margaret Cameron.

This stage of evolutionary thought began with the publication in August 1858 of a joint work by Darwin and Wallace, which was followed in 1859 by Darwin's book The Origin of Species, in the one that designates the principle of natural selection as the main engine of the evolutionary process and accepts the Lamarckian thesis of the inheritance of acquired characters as a source of biological variability; For this reason, although Wallace rejected Lamarckism, the name "Lamarck-Darwin-Wallace" is accepted to refer to this stage.

Darwin used the expression "descent with modification" instead of "evolution". Partly influenced by Thomas Malthus's Essay Concerning the Principle of Population (1798), Darwin noted that population growth would lead to a "struggle for existence" in which favorable variations prevailed while others perished. In each generation, many offspring fail to survive to breeding age due to limited resources. This could explain the diversity of plants and animals from a common ancestor through the operation of natural laws in the same way for all types of organisms.

Reading of the first paragraph of the Darwinism section

The Origin of Species contained "a most ingenious theory to explain the appearance and perpetuation of varieties and specific forms on our planet" in the words of the prologue written by Charles Lyell (1797- 1895) and William Jackson Hooker (1785-1865). In fact, this work presented for the first time the hypothesis of natural selection. This hypothesis contained five fundamental statements:

all organisms produce more offspring than the environment can sustain;
There is abundant intraspecific variability for most characters;
competition for limited resources leads to struggle "for life" (according to Darwin) or "for existence" (according to Wallace);
decrease occurs with inheritable modifications
and as a result, new species originate.

Darwin developed his theory of "natural selection" from 1838 and was writing his "great book" on the subject when Alfred Russel Wallace sent him a version of much the same theory in 1858. Their separate papers were presented together at an 1858 meeting of the Linnean Society in London. Lyell and Hooker credited Darwin as the first to formulate the ideas. presented in joint work, attaching as evidence an 1844 essay by Darwin and a letter he sent to Asa Gray in 1857, both published together with an article by Wallace. A detailed comparative analysis of Darwin's and Wallace's publications reveals that the latter's contributions were more important than is usually acknowledged, Thomas Henry Huxley applied Darwin's ideas to humans, using paleontology and comparative anatomy. to provide strong evidence that humans and apes shared a common ancestor.

Thirty years later, the co-discoverer of natural selection published a series of lectures under the title of "Darwinism" that deal with the same topics that Darwin had already dealt with, but in the light of facts and data that were unknown at the time of Darwin, who died in 1882. However, in his Origin of Species' , Darwin was the first to summarize a coherent set of observations that solidified the concept of evolution. of life in a true scientific theory ―that is, in a system of hypotheses―.

The list of Darwin's proposals presented in this work is shown below:

1. The supernatural acts of the Creator are incompatible with the empirical facts of nature.
2. All life evolved from one or a few simple forms of organisms.
3. Species evolve from pre-existing varieties through natural selection.
4. The birth of a species is gradual and long lasting.
5. Upper taxons (geners, families, etc.) evolve through the same mechanisms as those responsible for the origin of species.
6. The greater the similarity between the taxa, the more closely related they are among themselves and the shorter the time of their divergence from the last common ancestor.
7. Extinction is mainly the result of interspecific competition.
8. The geological record is incomplete: the absence of forms of transition between species and higher-ranking taxa is due to gaps in current knowledge.

Darwin's great achievement was to show that it is possible to explain apparent teleology in non-teleological terms or ordinary causal terms. Life is not directional, it is not directed in advance.

Neo-Darwinism

Modern evolutionary synthesis

Main article: Modern evolutionary synthesis

Julian Huxley gave his name in 1942 to the synthetic theory of evolution, which is now widely accepted in the scientific community.

This system of hypotheses of the evolutionary process originated between 1937 and 1950. In contrast to the neo-Darwinism of Weismann and Wallace, which gave primacy to natural selection and postulated Mendelian genetics as the mechanism for the transmission of traits between generations, the synthetic theory incorporated data from various fields of biology, such as molecular genetics, systematics and paleontology and introduced new mechanisms for evolution. For these reasons, these are different theories although the terms are sometimes used interchangeably.

According to the vast majority of historians of Biology, the basic concepts of the synthetic theory are essentially based on the content of six books, whose authors were: the Russian-American naturalist and geneticist Theodosius Dobzhansky (1900-1975); the German-American naturalist and taxonomist Ernst Mayr (1904-2005); British zoologist Julian Huxley (1887-1975); the American paleontologist George G. Simpson (1902-1984); the German zoologist Bernhard Rensch (1900-1990) and the American botanist George Ledyard Stebbins (1906-2000).

The terms «evolutionary synthesis» and «synthetic theory» were coined by Julian Huxley in his book Evolution: The Modern Synthesis (1942), in which he also introduced the term Evolutionary Biology instead of the phrase "study of evolution". In fact, Huxley was the first to point out that evolution "should be considered the most central and most important problem of biology and whose explanation should be approached through facts and methods from every branch of science, from ecology, genetics, paleontology, embryology, systematics to comparative anatomy and geographical distribution, without forgetting those of other disciplines such as geology, geography and mathematics".

The so-called "modern evolutionary synthesis" is a robust theory that currently provides explanations and mathematical models of the general mechanisms of evolution or evolutionary phenomena, such as adaptation or speciation. Like any scientific theory, its hypotheses are subject to constant criticism and experimental verification.^{[citation needed]}

The entities where evolution acts are the populations of organisms and not individuals. Theodosius Dobzhansky, one of the founders of modern synthesis, expressed the evolution as follows: "Evolution is a change in the genetic composition of populations. The study of evolutionary mechanisms corresponds to population genetics." This idea led to the "biological concept of species" developed by Mayr in 1942: a community of populations interspersed and reproductively isolated from other communities.
Phenotypic and genetic variability in plant and animal populations is produced by genetic recombination—reorganization of chromosome segments during sexual reproduction—and random mutations. The amount of genetic variation that a population of organisms with sexual reproduction can produce is enormous. Consider the possibility of a single individual with a "N" number of genes, each with only two alleles. This individual can produce 2^N sperm or genetically different eggs. Because sexual reproduction involves two parents, each descendant can, therefore, own one of the 4^N different combinations of genotypes. Thus, if each parent has 150 genes with two alleles each—a human genome underestimation—each parent can give rise to more than 10⁴⁵ genetically different gametes and more than 10⁹⁰ genetically different descendants.^{[chuckles]required]}

Natural selection is the most important force modeling the course of phenotypic evolution. In changing environments, the directional selection is of particular importance, because it produces a change in the average population towards a new phenotype that best adapts to altered environmental conditions. In addition, in small populations, random gene derivation—the loss of genes from genetic acquis—can be significant.^{[chuckles]required]}

Speciation can be defined as “a step in the evolutionary process (in which) the forms... become incapable of hybridizing”. Various mechanisms of reproductive isolation have been discovered and studied in depth. It is believed that the geographical isolation of the founding population is responsible for the origin of new species in the islands and other isolated habitats and it is likely that the alopatric spice—the divergent evolution of populations that are geographically isolated from each other—is the predominant spice mechanism in the origin of many animal species. However, simpatric spice—the emergence of new species without geographical isolation—is also documented in many taxa, especially in vascular plants, insects, fish and birds.

Evolutionary transitions in these populations are usually gradual, i.e. new species evolve from pre-existing varieties through slow processes and at each stage their specific adaptation is maintained.^{[chuckles]required]}

Macroevolution—phylogenetic evolution above the species level or the appearance of higher taxa—is a gradual, step-by-step process, which is only the extrapolation of microevolution—the origin of races and varieties, and of species—.^{[chuckles]required]}

Punctuated balance

This section is a punched Balance extract.[chuckles]edit]

In evolutionary biology, the theory of punctured balance, also called interrupted balance, is a theory that proposes that once a species appears in the fossil record, the population stabilizes, showing few evolutionary changes during most of its geological history. This minimal or no morphological state of change is called stasis. According to theory, significant evolutionary changes are rare and geologically rapid events of branched spice called cladogenesis. Cladogenesis is the process by which a species is divided into two different species, rather than gradually transformed into another.

The punctured balance is commonly contrasted with philtic gradualism, the idea that evolution usually occurs uniformly and by the constant and gradual transformation of full lineages (called anagenesis). From this point of view, evolution is generally considered gradual and continuous.

In 1972, the paleontologists Niles Eldredge and Stephen Jay Gould developed this theory in a historic article entitled “Punctuated equilibria: an alternative to phyletic gradualism” (“Putted balances: an alternative to philtic gradualism”). The article was based on the model of geographical spice of Ernst Mayr, the theories of genetic homeostasis and the development of Michael Lerner, and his own empirical research. Eldredge and Gould proposed that the degree of gradualism commonly attributed to Charles Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species. Elisabeth Vrba's change pulse hypothesis supports Eldredge and Gould's theory.

Neutralist theory of molecular evolution

This section is an extract from the neutralist theory of molecular evolution.[chuckles]edit]

The neutralist theory of molecular evolution states that the vast majority of evolutionary changes at the molecular level are caused by the genetic drift of neutral mutants in terms of natural selection. The theory was proposed by Moto Kimura in 1968 and described in detail in 1983 in his book The Neutral Theory of Molecular Evolution, and although it was received by some as an argument against Darwin's theory of evolution through natural selection, Kimura maintained (with the agreement of the majority of those who work in evolutionary biology) that the two theories are compatible: "The theory does not deny the role of natural selection in the determination of the course of adaptive evolution". In any case, the theory attributes a great role to genetic drift.

Evolutionary Developmental Biology

This section is an extract of evolutionary Biology of development.[chuckles]edit]

Ernst Haeckel embryo drawings

Evolutionary Biology of Development (or Informally evo-devoEnglish evolutionary developmental biology) is a field of biology that compares the development process of different organisms in order to determine their phylogenetic relationships. Likewise, evo-devo, seeks to identify the mechanisms of development that give rise to evolutionary changes in the phenotypes of individuals (Hall, 2003). The main interest of this new evolutionary approach is to understand how the organic form (new structures and new morphological patterns) evolves. Thus, evolution is defined as the change in development processes.

The approach adopted by evo-devo is multidisciplinary, confluing disciplines such as the biology of development (including development genetics), evolutionary genetics, systematic, morphology, comparative anatomy, paleontology and ecology.

Modern evolutionary synthesis

Main article: Modern evolutionary synthesis

In Darwin's day, scientists did not know how traits were inherited. Subsequently, most hereditary characteristics were discovered to be related to persistent entities called genes, fragments of the linear deoxyribonucleic acid (DNA) molecules in the nucleus of cells. DNA varies among members of the same species and also undergoes changes, mutations, or rearrangements due to genetic recombination.

Variability

Main articles: Genetic Variability and Genetics of populations.

The phenotype of an individual organism is the result of its genotype and the influence of the environment in which it lives and has lived. A substantial part of the variation between phenotypes within a population is caused by differences between its genotypes. The modern evolutionary synthesis defines evolution as the change in that genetic variation over time. The frequency of each allele fluctuates, being more or less prevalent in relation to other alternative forms of the same gene. Evolutionary forces act by directing these changes in allele frequencies in one direction or another. Variation in a population for a given gene disappears when there is fixation of an allele that has entirely replaced all other alternative forms of that same gene.

Variability arises in natural populations by mutations in genetic material, migrations between populations (gene flow), and by reorganization of genes through sexual reproduction. Variability can also come from the exchange of genes between different species, for example through horizontal gene transfer in bacteria or interspecific hybridization in plants. Despite the constant introduction of new variants through these processes, most of the genome of a species is identical in all individuals belonging to it. However, even small changes in the genotype can lead to substantial changes in the phenotype. Thus, chimpanzees and humans, for example, only differ in about 5% of their genomes.

Mutation

Main article: Mutation

Duplication of part of a chromosome.

Darwin did not know the source of the variations in individual organisms, but he noted that they seemed to occur randomly. In later works, most of these variations were attributed to mutations. A mutation is a permanent, transmissible change in the genetic material—usually DNA or RNA—of a cell, produced by "miscopying" in the genetic material during cell division or by exposure to radiation, chemicals, or radiation. virus action. Random mutations constantly occur in the genome of all organisms, creating new genetic variability. Mutations may have no effect on the organism's phenotype, or may be deleterious or beneficial. By way of example, studies carried out on the fruit fly (Drosophila melanogaster) suggest that if a mutation determines a change in the protein produced by a gene, that change will be harmful in 70 % of cases and neutral or slightly beneficial in the rest.

The frequency of new mutations in a gene or DNA sequence in each generation is called the mutation rate. In scenarios of rapid environmental change, a high mutation rate increases the probability that some individuals have a suitable genetic variant to adapt and survive; on the other hand, it also increases the number of harmful or deleterious mutations that decrease the adaptation of individuals and raises the probability of extinction of the species. Due to the conflicting effects that mutations can have on organisms, the mutation rate optimal for a population is a trade-off between costs and benefits, which depends on the species and reflects evolutionary history in response to challenges imposed by the environment. Viruses, for example, have a high mutation rate, which It has an adaptive advantage since they must constantly and rapidly evolve to overcome the immune systems of the organisms they affect.

Gene duplication introduces extra copies of a gene into the genome, thereby providing the building blocks for the new copies to start their own evolutionary path. If the initial gene continues to function normally, its copies they can acquire new mutations without harm to the organism that hosts them and eventually adopt new functions. For example, in humans four genes are necessary to build the structures necessary to detect light: three for the vision of colors and one for night vision. All four genes have evolved from a single ancestral gene by duplication and subsequent divergence. Other types of mutation can occasionally create new genes from so-called non-coding DNA. New genes with different functions can also arise from fragments. of duplicated genes that recombine to form new DNA sequences.

Chromosomal mutations—also called chromosomal aberrations—are an additional source of heritable variability. Thus, translocations, inversions, deletions, Robertsonian translocations, and duplications usually cause phenotypic variants that are transmitted to offspring. For example, in the genus Homo a chromosome fusion took place that gave rise to chromosome 2 in humans, while other apes retain 24 pairs of chromosomes. Despite the phenotypic consequences that such chromosomal mutations, its greatest evolutionary importance lies in accelerating the divergence of populations that have different chromosomal configurations: the gene flow between them is severely reduced due to the sterility or semi-sterility of heterozygous individuals. In this way, chromosomal mutations act as reproductive isolation mechanisms that lead different populations to maintain their identity as species over time.

Fragments of DNA that can change position on chromosomes, such as transposons, make up a major fraction of the genetic material of plants and animals and may have played a prominent role in their evolution. By inserting into or cleaving from In other parts of the genome these sequences can activate, inhibit, delete or mutate other genes and thus create new genetic variability. Also, some of these sequences are repeated thousands or millions of times in the genome and many of them have adopted functions important, such as the regulation of gene expression.

Genetic recombination

Main article: Genetic recombination

Population genetics

As previously described, from a genetic point of view, evolution is an intergenerational change in the frequency of alleles within a population that shares the same genetic heritage. A population is a group of individuals of the same species. that share a geographic area. For example, all the moths of the same species that live in an isolated forest form a population. A given gene within the population can present various alternative forms, which are responsible for the variation between the different phenotypes of organisms. An example might be a coloration gene in moths that has two alleles: one for white and one for black. The heritage or gene pool is the complete set of alleles in a population, such that each allele appears a certain number of times in a gene pool. The fraction of genes in the genetic heritage that are represented by a given allele is called the allele frequency, for example, the fraction of moths in the population that have the allele for black color. Evolution occurs when there are changes in allele frequency in a population of interbreeding organisms, for example if the allele for black color becomes more common in a population of moths.

To understand the mechanisms that cause a population to evolve, it is helpful to know the conditions necessary for the population not to evolve. The Hardy-Weinberg principle states that the frequency of alleles in a sufficiently large population will remain constant only if the only force at work is random recombination of alleles during gamete formation and subsequent combining of alleles during fertilization. In this case, the population is in Hardy-Weinberg equilibrium and therefore does not evolve.

Gene flow

Main article: Genetic flow

When male lions reach sexual maturity, they leave the group in which they were born and set up in another herd to appear, which ensures the gene flow between herds.

Gene flow is the exchange of genes between populations, usually of the same species. Examples of gene flow include the interbreeding of individuals after the immigration of one population into the territory of another, or, in the case of plants, the exchange of pollen between different populations. Gene transfer between species involves the formation of hybrids or horizontal gene transfer.

The immigration and emigration of individuals in natural populations can cause changes in allelic frequencies, as well as the introduction ―or disappearance― of allelic variants within an already established gene pool. Physical separations in time, space, or specific ecological niches that may exist between natural populations restrict or disable gene flow. In addition to these restrictions on the exchange of genes between populations, there are other mechanisms of reproductive isolation made up of characteristics, behaviors, and physiological processes that prevent members of two different species from interbreeding or mating with each other, producing offspring, or preventing them from being viable or fertile. These barriers constitute an essential phase in the formation of new species since they maintain their own characteristics over time by restricting or eliminating gene flow between individuals of different populations.

Different species can be interfertile, depending on how far they have diverged from their common ancestor; for example, the mare and donkey can mate and produce the mule. Such hybrids are generally sterile due to chromosomal differences between the parent species, which prevent the correct pairing of chromosomes during meiosis. In this case, closely related species can regularly interbreed, but natural selection works against hybrids. However, from time to time, viable and fertile hybrids are formed that may have intermediate properties between their parent species or possess an entirely new phenotype.

The importance of hybridization in the creation of new species of animals is not clear, although there are well-documented examples such as the frog Hyla versicolor. Hybridization is, however, a important mechanism of formation of new species in plants, since they tolerate polyploidy - the duplication of all the chromosomes of an organism - more easily than animals; polyploidy restores fertility in interspecific hybrids because each chromosome it is capable of mating with an identical partner during meiosis.

There are two basic mechanisms of evolutionary change: natural selection and genetic drift. Natural selection favors genes that improve the organism's ability to survive and reproduce. Genetic drift is the change in the frequency of alleles, caused by the random transmission of genes from one generation to the next. The relative importance of natural selection and genetic drift in a population varies depending on the strength of selection and the effective population size, which is the number of individuals in that population capable of reproducing. Natural selection usually dominates in large populations, while genetic drift predominates in small ones. The prevalence of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations. As a result, changes in the size of a population can significantly influence the course of evolution. The so-called «bottlenecks», or temporary drastic decreases in the effective size of the population, suppose a loss or erosion of genetic variability and lead to the formation of genetically more uniform populations. Bottlenecks can be the result of catastrophes, variations in the environment, or alterations in gene flow caused by reduced migration, expansion into new habitats, or population subdivision.

Natural selection

Main article: Natural selection

Diagram showing how mutations and natural selection interact to cause changes in populations of organisms

Biston betularia shape typica

Biston betularia shape coal

The two ways typica and coal of the moth Biston betularia inns on the same trunk. The form typica, of light color, is hardly observable on this tree that is not blackened by the hollin, what the camouflage of predators, such as Parus major.

Natural selection is the process by which genetic mutations that enhance reproductive capacity become, and remain, increasingly frequent in successive generations of a population. It is often called a "self-evident mechanism" because it is the necessary consequence of three simple facts: (a) within populations of organisms there is heritable variation (b) organisms produce more offspring than can survive, and (c)) such offspring have different abilities to survive and reproduce.

The central concept of natural selection is the biological fitness of an organism. Fitness, fit, or fitness influences the extent of an organism's genetic contribution to the next generation. Fitness, however, is not simply equal to the total number of offspring of a given organism, as it also quantifies the proportion of subsequent generations that carry that organism's genes. For example, if an organism can survive and reproduce, but its offspring are too small or unhealthy to reaching reproductive age, the genetic contribution of that organism to future generations will be very low and, therefore, its fitness is also very low.

Therefore, if one allele increases fitness more than others, with each generation the allele will become more common within the population. Such traits are said to be "favourably selected." An improvement in survival or increased fecundity are examples of traits that can increase fitness. Conversely, lower fitness caused by a less beneficial or deleterious allele causes it to become increasingly rare in the population and suffer "negative selection". It should be stressed that the fitness of an allele is not a fixed characteristic: if as the environment changes, traits that were previously neutral or harmful may become beneficial, and vice versa. another dark called carbonaria form. The typica form, as its name indicates, is the most frequent in this species. However, during the industrial revolution in the UK the trunks of many trees on which the moths roosted were blackened by soot, giving the dark-coloured moths a better chance of surviving and producing more offspring by spending more time easily unnoticed by predators. Just fifty years after the first melanic moth was discovered, almost all of the moths in the Manchester industrial area were dark. This process was reversed by the "Clean Air Act" of 1956, which reduced industrial pollution. As the color of the trunks lightened, the dark moths again became more easily visible to predators and their numbers decreased. However, even if the direction of selection changes, traits that would have been lost in the past cannot be restored. obtained in an identical way ―a situation described by Dollo's Law or "Law of evolutionary irreversibility"―. According to this hypothesis, a structure or organ that has been lost or discarded during the course of evolution will not appear again in the future. that same lineage of organisms.

According to Richard Dawkins, this hypothesis is "a statement about the statistical improbability of following exactly the same evolutionary trajectory twice, or indeed the same particular trajectory in both directions".

Within a population, natural selection for a certain continuously varying trait, such as height, can be categorized into three different types. The first is "directional selection," which is a change in the mean value of a trait over time; for example, when organisms grow taller. Second is "disruptive selection" which is the selection for extreme values of a certain trait, often resulting in extreme values being more common and the selection works against the average value; this implies, in the example above, that short and tall organisms have an advantage, but those of medium height do not. Finally, in the "stabilizing selection", the selection acts against the extreme values, which determines a decrease in the variance around the average and a lower variability of the population for that particular character; selection, all organisms in a population would gradually acquire a similar height.^{[citation needed]}

A special type of natural selection is sexual selection, which acts in favor of any trait that increases reproductive success by increasing an organism's attractiveness to potential mates. Certain traits acquired by males through sexual selection—such such as bulky horns, mating songs, or bright colors—can reduce the chances of survival, for example by attracting predators. However, this reproductive disadvantage is offset by greater reproductive success for males exhibiting these traits.

An active study area is the so-called «selection unit»; natural selection has been said to act at the level of genes, cells, individual organisms, groups of organisms, and even species. None of these models is mutually exclusive, and selection can act at multiple levels at once. For example, below the level of the individual, there are genes called transposons that attempt to replicate throughout the genome. Selection above the level of the individual, such as group selection, may allow the evolution of cooperation.

Genetic drift

Main article: Genetic derogation

Simulation of the genetic drift of twenty wings not linked in populations of 10 (up) and 100 (low). The drift towards fixation is faster in the small population.

Genetic drift is the change in the frequency of alleles between one generation and the next, and it occurs because the alleles of the offspring are a random sample of the parents, and because of the role that chance plays in timing. to determine if a given individual will survive and reproduce. In mathematical terms, alleles are subject to sampling error. As a result, when selective forces are absent or relatively weak, allele frequencies tend to "drift" up or down randomly (in a random walk). This drift stops when an allele finally becomes fixed, that is, it either disappears from the population or completely replaces the rest of the genes. Thus, genetic drift can eliminate some alleles from a population simply due to chance. Even in the absence of selective forces, genetic drift can cause two separate populations that start out with the same genetic makeup to split into two divergent populations with a different set of alleles.

The time required for an allele to become fixed by genetic drift depends on the size of the population; fixation occurs faster in smaller populations. The precise measurement of populations that is important in this case is called the effective population size, which was defined by Sewall Wright as the theoretical number of breeding individuals of the same degree. consanguinity observed.

Although natural selection is responsible for adaptation, the relative importance of the two forces, natural selection and genetic drift, as drivers of evolutionary change in general is currently a field of research in evolutionary biology. These investigations were inspired by by the neutralist theory of molecular evolution, which postulates that most evolutionary changes result from the fixation of neutral mutations, which have no immediate effect on an organism's fitness. Thus, in this model, most of genetic changes in a population are the result of constant mutation pressure and genetic drift.

The consequences of evolution

Adaptation

Homologist bones of tetrapod extremities. The bones of the four animals have the same basic structure, but have been adapted to specific uses.

Adaptation is the process by which a population becomes more adapted to its habitat and also the change in the structure or function of an organism that makes it more adapted to its environment. This process occurs by selection natural for many generations and is one of the basic phenomena of biology.

The importance of an adaptation can only be understood in relation to the total biology of the species. Julian Huxley

Species tend to adapt to different ecological niches to minimize competition between them. This is known as the principle of competitive exclusion in ecology: two species cannot occupy the same niche in the same environment for a long time.

Adaptation does not necessarily imply major changes in a physical part of a body. As an example, we can mention the flukes ―internal parasites with very simple body structures, but with a very complex life cycle― in which their adaptations to such an unusual environment are not the product of characters observable with the naked eye but in critical aspects. of their life cycle. In general, the concept of adaptation includes, in addition to the adaptive process itself, all aspects of the organisms, populations or species that are its result. By using the term «adaptation» for the evolutionary process and “adaptive trait or character” for its product, the two senses of the concept are perfectly distinguished. According to Theodosius Dobzhansky, "adaptation" is the evolutionary process by which an organism becomes more capable of living in its habitat or habitats, while "adaptability" is the state of being adapted, that is, the degree to which an organism organism is capable of living and reproducing in a given set of habitats. Finally, an "adaptive trait" is one of the aspects of an organism's development that increases its likelihood of surviving and reproducing.

Adaptation sometimes involves gaining a new feature; notable examples are the laboratory evolution of Escherichia coli bacteria so that they may be able to use citric acid as a nutrient, when wild-type bacteria cannot; the evolution of a new enzyme in Flavobacterium that allows these bacteria to grow on the by-products of nylon manufacturing; and the evolution of an entirely new metabolic pathway in the soil bacterium Sphingobium which allows it to break down the synthetic pesticide pentachlorophenol. Sometimes, loss of an ancestral function can also occur. An example that shows both types of change is the adaptation of the bacterium Pseudomonas aeruginosa to fluoroquinolone with genetic changes that modify the molecule on which it acts and by increasing the activity of the transporters that pump the antibiotic outside the cell. An idea that is still controversial is that some adaptations can increase the ability of organisms to generate genetic diversity and to adapt by natural selection ―in other words, they would increase the ability to evolve―.

A whale skeleton, a and b bones of the fin, which are adaptations of front leg bones, while c indicates the vestigeal bones of the rear legs, which suggests an adaptation from the terrestrial to aquatic habit.

A consequence of adaptation is the existence of structures with similar internal organization and different functions in related organisms. This is the result of modifying an ancestral structure to adapt it to different environments and ecological niches. The wing bones of bats, for example, are very similar to those of mouse feet and primate hand bones, because all of these structures were present in a common mammalian ancestor. all living organisms are related to some degree, even structures that differ profoundly, such as the eyes of arthropods, squid, and vertebrates, or the limbs and wings of arthropods and vertebrates, depend on a common set of genes homologs that control their development and function, called deep homology.

During adaptation, vestigial structures may appear, lacking functionality in a species; however, the same structure is functional in the ancestral species or in other related species. Examples include pseudogenes, the eyes of blind cave fish, wings in flightless bird species, and the hip bones present in whales and snakes. Examples also exist in humans. of vestigial structures, such as wisdom teeth, tailbone, vermiform appendix, and involuntary reactions such as goosebumps and other primitive reflexes.

Some features that appear to be simple adaptations are, in fact, exaptations: structures originally adapted for one function, but coincidentally made useful for another purpose. An example is the African lizard Holaspis guentheri which developed a very flattened head and trunk to hide in crevices, as can be seen in other lizards of the same genus. However, in this species, the flattened body allows it to glide from tree to tree. The lungs of ancestral lungfishes are an exaptation of the swim bladders of teleost fish used as a buoyancy regulator.

A branch of evolutionary biology studies the development of adaptations and exaptations. This area of research addresses the origin and evolution of embryonic development and how new features arise from developmental modifications. These studies have shown, for example, that the same bone structures in embryos that are part of the jawbone in some animals are instead part of the middle ear in mammals. Changes in genes that control development can also cause lost structures to reappear during evolution, such as the teeth of mutant chicken embryos, similar to those of crocodiles. In fact, it is becoming increasingly clear that most alterations in the shape of organisms are due to changes in a small set of conserved genes.

Coevolution

Main article: Coevolution

The interaction between organisms can produce conflict or cooperation. When two different species interact, such as a pathogen and a host, or a predator and its prey, the evolution of one causes adaptations in the other; these changes in the second species cause, in turn, new adaptations in the first. This cycle of selection and response is called coevolution. An example is the production of tetrodotoxin by the Oregon newt and the evolution of resistance to this toxin in its predator, the garter snake. In this predator-prey pairing, the evolutionary arms race (Red Queen Hypothesis) has resulted in increased toxin production in the newt, and a corresponding increase in resistance to it in the snake. An example of coevolution that did not involves competition (Red King Hypothesis) are symbiotic and mutualistic interactions between mycorrhizae and plant roots or bees and the plants they pollinate. Another example of an entity that coevolves with its host is viruses with cells. Cells usually develop defenses in their immune system to avoid viral infections, however viruses must mutate quickly in order to avoid these cellular defenses or the host's immune system. Therefore, viruses are the only entities that evolve faster than any other for their existence. Viruses are entities that can only evolve and survive in cells. According to recent studies, they have been coevolving with cells since their origins (protobiont) and therefore their origin is prior to that of the last universal common ancestor. Viruses could have arisen in these protobionts or before, to later serve as a means of horizontal gene transfer (mobile genetic element) and regulate the population of certain cellular organisms. In fact, new types of viruses could also have emerged during different stages of evolution, through various molecular mechanisms such as recombinations between mobile genetic elements with other viruses. They can even jump between various cellular organisms and acquire new hosts.

Speciation

Main article: Spice

Speciation (or cladogenesis) is the process by which a species diverges into two or more descendant species. Evolutionary biologists view species as statistical phenomena and not as categories or types. This approach is contrary to the still deeply rooted classical concept of a species as a class of organisms exemplified by a "type specimen" that possesses all the characteristics common to that species. Instead, a species is now thought of as a lineage that shares a single gene pool and evolves independently. According to this description, the boundaries between species are blurred, although both genetic and morphological properties are used to help differentiate between closely related lineages. In fact, the exact definition of the term "species" is still under debate, particularly for organisms based on prokaryotic cells; it is what is called the "species problem". Various authors have proposed a series of definitions based on different criteria, but the application of one or the other is finally a practical matter, depending on each case. of the particularities of the group of organisms under study. Currently, the main unit of analysis in biology is the population, an observable set of interacting individuals, rather than the species, an observable set of individuals that resemble each other.^{[citation needed]}

It illustrates the spatial aspects of different modes of speciation. Alopatric spice: a physical barrier divides the population. peripatric species: a small founding population conquers an isolated niche. Parapolistic spice: a part of the original population conquers a new adjacent niche. Sympathy: Speciation occurs without physical separation.

Speciation has been observed on multiple occasions both under controlled laboratory conditions and in nature. In sexually reproducing organisms, speciation is the result of reproductive isolation followed by genealogical divergence. There are four modalities of speciation. The most common in animals is allopatric speciation, which takes place in populations that remain geographically isolated, as in the case of habitat fragmentation or migrations. Under these conditions, selection can cause very rapid changes in the appearance and behavior of organisms. Due to the processes of selection and genetic drift, the separation of populations can result in offspring that cannot reproduce between them.

The second modality of speciation is peripatric speciation, which occurs when small populations become isolated in a new environment. It differs from allopatric speciation in that the isolated populations are numerically much smaller than the parent population. This causes rapid speciation by accelerating genetic drift and selection on a small gene pool, a process known as the founder effect.

The third modality of speciation is parapatric speciation. It is similar to peripatric speciation in that a small population colonizes a new habitat, but differs in that there is no physical separation between the two populations. Instead, speciation is the result of the evolution of mechanisms that reduce gene flow between the two populations. Generally, this occurs when there has been a drastic change in the environment within the habitat of the parent species. An example is the grass Anthoxanthum odoratum, which can undergo parapatric speciation in response to localized metal contamination from mines. In this case, plants evolve with a resistance to high levels of metals in the soil; Reproductive isolation occurs because selection favors a flowering season different from that of the parent species for the new plants, which cannot then lose the genes that give them resistance through hybridization. Selection against hybrids can be enhanced by differentiation of traits that promote reproduction between members of the same species, as well as by increasing differences in appearance in the geographic area in which they overlap.

Finally, in sympatric speciation, species diverge without geographic isolation or habitat change. This pattern is rare, as even a small amount of gene flow can eliminate genetic differences between parts of a population. In general, in animals, sympatric speciation requires the evolution of genetic differences and non-random mating, for it to occur. may develop reproductive isolation.

One type of sympatric speciation is the crossing of two related species to produce a new hybrid species. This is unusual in animals, because homologous chromosomes from parents of different species cannot successfully pair during meiosis. It is most common in plants, which often double their chromosome number to form polyploids. This allows the chromosomes from each parent species to form a complementary pair during meiosis, since each parent's chromosomes are already represented by one pair. An example of this type of speciation occurred when the plant species Arabidopsis thaliana and Arabidopsis arenosa interbred to produce the new species Arabidopsis suecica. This took place approximately 20,000 years ago, and the speciation process has been reproduced in the laboratory, which has made it possible to study the genetic mechanisms involved in this process. In fact, the duplication of chromosomes within a species can be a common cause of reproductive isolation, as half of the duplicated chromosomes will be unpaired when they mate with those of unduplicated organisms.

Episodes of speciation are important in the theory of punctuated equilibrium, which explains the presence in the fossil record of rapid moments of speciation interspersed with relatively long periods of stasis, during which species remain largely unchanged. In theory, speciation is related to rapid evolution, and natural selection and genetic drift act particularly strongly on organisms that undergo speciation in new habitats or small populations. As a result, periods of stasis in the fossil record correspond to the parent population, and organisms that undergo rapid evolution and speciation are found in small populations or geographically restricted habitats, thus rarely being preserved as fossils.

Extinction

Main article: Extinction

Extinction is the disappearance of an entire species. This is not an unusual event, and in fact, virtually all animal and plant species that have ever lived on Earth are now extinct, so it seems that extinction is the ultimate fate of all species. Extinctions they occur continuously throughout the history of life, although the rate of extinction increases dramatically in the occasional extinction event. The Cretaceous–Tertiary extinction, during which the dinosaurs went extinct, is the best known, but the earlier Permo extinction -Triassic was even more severe, causing the extinction of almost 96% of species. The Holocene extinction is still ongoing and is associated with humanity's expansion across the globe in recent millennia. The current rate of extinction is 100 to 1,000 times the average rate, and up to 30% of species may be extinct by mid-century XXI. Human activities are currently the leading cause of extinction; global warming may further accelerate it in the future.

The causes of extinction determine its impact on evolution. Most extinctions, which occur continuously, could be the result of competition between species for limited resources (competitive exclusion). If competition between species alters the probability of extinction, species selection could be considered a level of natural selection. Intermittent mass extinctions are also important, but instead of acting as a selective force, they drastically reduce diversity indiscriminately and promote explosions of extinction. rapid evolution and speciation in survivors.

Microevolution and macroevolution

Main articles: Microevolution and Macroevolution.

Microevolution is a term used to refer to small-scale changes in gene frequencies in a population over the course of several generations. The adaptation of insects to the use of pesticides or the variation in the skin color of humans are examples of microevolution. These changes can be due to several processes: mutation, gene flow, genetic drift or natural selection. Population genetics is a branch of evolutionary biology that applies biostatistical methods to the study of microevolutionary processes, such as skin color in the world population.^{[citation needed]}

Changes on a larger scale, from speciation to large evolutionary transformations that occur over long periods of time, are commonly called macroevolution. The evolution of amphibians from a group of bony fish is an example of macroevolution. Biologists do not usually make an absolute separation between macroevolution and microevolution, considering that macroevolution is simply cumulative microevolution over large time scales. A minority of theorists, however, consider that the synthetic theory mechanisms for microevolution are not sufficient to make that extrapolation and that other mechanisms are needed. The theory of punctuated equilibria, proposed by Gould and Eldredge, attempts to explain certain macroevolutionary trends observed in the fossil record.

Phylogeny

Main article: Philogenia

Phylogeny is the relationship of kinship between species or taxa in general. Although the term also appears in historical linguistics to refer to the classification of human languages according to their common origin, the term is mainly used in its biological sense. Phylogenetics is a discipline of evolutionary biology that deals with understanding the historical relationships between different groups of organisms from the distribution in a tree or dichotomous cladogram of the characters derived (synapomorphies) from a common ancestor to two or more taxa that contains those plesiomorphic characters in common.^{[citation needed]}

Monophily, paraphily and polyphily

This section is an extract from Filogenia § Monophilia, paraphilia and polyphilia.[chuckles]edit]

Phylogenetic groups: monophylaxis, paraphylaxis, polyphylaxis.

A group formed by an ancestor and all of its descendants is called monophytic, also called clado. The group that has been excluded from any of its descendants is called paraphylaxis. The groups formed by the descendants of more than one ancestor are called polyphiletics.^{[chuckles]required]}
For example, birds and reptiles are believed to descend from a single common ancestor, then this taxonomic group (yellow in the diagram) is considered monophytic. Current reptiles as a group also have an ancestor common to all of them, but that group (modern reptiles) does not include all the descendants of such ancestor because the birds are being left out (only includes the cian color in the diagram), such a group we say^{[chuckles]Who?]} that's paraphylactic. A group that would include hot-blood vertebrates would contain only mammals and birds (red/orange in the diagram) and would be polyphylactic, because among the members of this group there is not the most recent common ancestor of them. Hot-blooded animals are all descendants of a cold-blooded ancestor. The endothermal condition ("hot blood") has appeared twice, independently, in the ancestor of the mammals, on the one hand, and in the bird's (and perhaps some or all dinosaurs), on the other.^{[chuckles]required]}
Some authors claim^{[chuckles]Who?]} that the difference between paraphiletic and polyphiletic groups is subtle, and they prefer to call these two types of shakings as "non-monophyletic." Many long-recognized taxons of plants and animals turned out to be non-monophytic according to the phylogen analysis done in recent decades, so many scientists recommended abandoning their use, examples of these taxa are Prokaryota, Protista, Pisces, Reptilia, Pteridophyta, Dicotyledoneae, and several others. Since their use is widespread because they have been traditionally recognized, and because many scientists consider valid paraphylline taxa (discussion that is not yet completed in the scientific environment, the clearest example of a taxon that many^{[chuckles]Who?]} they wish to retain the reptiles, sometimes the name of the taxon is indicated, with the exception that their name is placed in quotation marks, to indicate that the taxon does not correspond with a claw.^{[chuckles]required]}

Extension of the modern synthesis

In recent decades it has become evident that evolutionary patterns and mechanisms are much more varied than those postulated by the pioneers of evolutionary biology (Darwin, Wallace or Weismann) and the architects of synthetic theory (Dobzhansky, Mayr and Huxley, among others). New concepts and information in the molecular developmental biology, systematics, geology, and fossil record of all groups of organisms need to be integrated into what has been called "extended evolutionary synthesis." The aforementioned fields of study show that evolutionary phenomena cannot be understood solely through the extrapolation of the processes observed at the level of modern populations and species. of the modern synthesis.

Paleobiology and rates of evolution

Average species lengths
in various groups of agencies.
Group of agencies	Average longevity (in millions of years)
Marine bivalves and gastropods	10-14
Foraminiferous and planktonic	20 to 30
Marine diatoms	25
Trilobits (extinguished).	▪ 1
Amonites (extinguished).	5
Freshwater fish	3
Snakes	▪
Mammals	1-2
Briophites	▪ 20
Higher plants. Herbs	3-4
Angiospermas. Trees and bushes	27-34
Gimnospermas. Conifers and cicadas	54

At the time that Darwin proposed his theory of evolution, characterized by small and successive modifications, the available fossil record was still very fragmentary and no fossils had been found prior to the Cambrian period. Darwin's dilemma, that is, the apparent non-existence of Precambrian fossil records, was used as the main argument against his proposal that all organisms on Earth come from a common ancestor.

In addition to the lack of ancient fossils, Darwin was also concerned about the lack of intermediate forms or connecting links in the fossil record, which challenged his gradualistic view of speciation and evolution. In fact, in Darwin's time, with the exception of Archaeopteryx, which shows a mixture of bird and reptilian characteristics, virtually no other examples of intermediate forms or missing links, as they were colloquially called, were known..

Even in 1944, when Simpson's book Tempo and mode in evolution was published, no Precambrian fossils were yet known and only a few examples of intermediate forms were available in the fossil record that link the ancient forms with the modern ones. Since then scientists have explored the Precambrian period in detail and it is known that life is much older than was believed in Darwin's time. It is also known that these ancient life forms were the ancestors of all subsequent organisms on the planet. Also, since the end of the XX century, a large number of representative examples of intermediate fossil forms linking to the main groups of vertebrates and even fossils of the first flowering plants. As a result of these and other scientific advances, a new discipline of paleontology has emerged, called paleobiology.

An example of a transitional form between fish and amphibians is the extinct genus Panderichthys, which inhabited the earth about 370 million years ago and is the intermediate link between Eustenopteron (a 380-million-year-old fish genus) and Acanthostega (363-million-year-old amphibians). Among terrestrial animals, the genus Pederpes arose 350 million years ago. years, connecting the major aquatic amphibians of the Late Devonian to early tetrapods. Likewise, the evolutionary history of several groups of extinct organisms, such as the dinosaurs, has been reconstructed in remarkable detail. An example of a link between synapsids non-mammals and mammals is Thrinaxodon, a mammalian-like synapsid that inhabited the planet 230 million years ago. The Microraptor, a four-winged dromaeosaurid that could plan and who lived 126 million years ago, represents an intermediate state between theropods and primitive flying birds such as Archaeopteryx. A transitional form between land mammals and the sea cow is Pezosiren, a primitive quadrupedal mermaid with terrestrial and aquatic adaptations that lived hoofed land mammals and whales are connected through the extinct genera Ambulocetus and Rodhocetus that inhabited the planet 48 to 47 million years ago To complete this list of examples of transitional forms, the common ancestor of chimpanzees and humans is the genus Sahelanthropus, an ape-like hominid that exhibited a mosaic of characters from chimpanzee and hominin and inhabited Africa 7 to 5 million years ago.

In his book Variation and evolution in plants (1950), Stebbins also lamented the absence of a fossil record that would allow us to understand the origin of the first flowering plants, the angiosperms. In fact, Darwin himself characterized the origin of angiosperms as an "abominable mystery." However, this knowledge gap is rapidly being filled with discoveries from the late XX century to the present. In 1998, in China, in the strata from the Upper Jurassic (more than 125 million years old), a fossil of an axis with fruits was discovered, which has been called Archaefructus This discovery, which allows establishing the age of the oldest angiosperms, made the Yixian Formation, where this fossil was found, world famous. In the same formation, the fossil of another angiosperm, Sinocarpus, was found, and, in 2007, a flower that presents the typical organization of angiosperms, with the presence of tepals, stamens and gynoecium. This species has been named Euanthus (Greek for "true flower") by its discoverers, and shows that flowers like those of today's angiosperms already existed in the early Cretaceous.

Environmental causes of mass extinctions

Mass extinctions have played a key role in the evolutionary process

Darwin not only considered the origin, but also the decline and disappearance of species; he proposed that interspecific competition for limited resources was a major cause of population and species extinction: over evolutionary time, superior species would emerge to replace less-adapted species. This perspective has changed in recent years, with a better understanding of the causes of mass extinctions, episodes in Earth's history, where the "rules" of natural selection seem to be broken. Mayr put forward the new perspective in his book Animal species and evolution , in which he noted that extinction should be considered one of the most conspicuous evolutionary phenomena. Mayr discussed the causes of extinction events and speculated that the emergence of new diseases, the invasion of an ecosystem by other species, or changes in the biotic environment may be responsible:

"The real causes of extinction of any kind of fossil will presumably always remain uncertain... It is true, however, that any serious extinction event is always correlated with an important environmental disorder" (May, 1963).

This hypothesis, unsupported by proven facts when it was proposed, has since acquired considerable support. The term "mass extinction", mentioned by Mayr without an associated definition, is used when a large number of species become extinct in a geologically short time; events may be related to a single cause or a combination of causes, and extinct species are plants and animals of all sizes, both marine and terrestrial. At least five mass extinctions have occurred: the Cambrian-Ordovician mass extinction, the Ordovician-Silurian mass extinctions, the Devonian mass extinction, the Permian-Triassic mass extinction, and the Cretaceous-Tertiary mass extinction.

The biological extinction that occurred in the Permian-Triassic about 250 million years ago represents the most severe extinction event in the last 550 million years. It is estimated that about 70% of terrestrial vertebrate families, many woody gymnosperms, and more than 90% of oceanic species went extinct in this event. Various causes have been proposed to explain this event, such as volcanism, asteroid or comet impact, oceanic anoxia, and environmental change. However, it is now apparent that gigantic volcanic eruptions, which occurred over a time interval of only a few hundred thousand years, were the primary cause of the late Permian catastrophe of the biosphere. Cretaceous-Tertiary records the second largest mass extinction event. This global catastrophe wiped out 70% of all species, among which dinosaurs are the most popularly known example. Small mammals survived to inherit vacant ecological niches, allowing for the rise and adaptive radiation of lineages that would ultimately become Homo sapiens and other living species. Paleontologists have proposed numerous hypotheses to explain this event; the most accepted at present are those of the impact of an asteroid and that of volcanism.

In summary, the hypothesis of environmental disturbances as causes of mass extinctions has been confirmed, indicating that while much of evolutionary history may be gradual, from time to time catastrophic events have set its pace background. It is evident that the few "lucky survivors" determine the subsequent patterns of evolution in the history of life.

Sexual selection and altruism

Main articles: Sexual assault, Cooperation (evolution) and Biological altruism.

Male real bird with all its deployed plumage

Certain characteristics in a species are sexually attractive even if they lack another adaptive meaning. For example, the attraction of the females of some bird species to the males most capable of inflating their necks has resulted, over the generations, in the selection of males that can inflate their necks to an extraordinary level. Darwin concluded that while natural selection guides the course of evolution, sexual selection influences its course even though there seems to be no obvious reason for it. Darwin's arguments in favor of sexual selection appear in the fourth chapter of The Origin of Species and, most especially, in The Descent of Man, and Selection in Relation to Sex of 1871. In both cases, the analogy with the artificial world is used:

[Sex selection] does not depend on a struggle for existence but on a struggle between males for the possession of females; the result is not the death of the competitor who has not succeeded, but having little or no offspring. Sexual selection is therefore less rigorous than natural selection. Generally, the most vigorous males, those who are best suited to the places they occupy in nature, will leave greater progenie. But in many cases victory will not depend on vigor but on the exclusive special weapons of the male sex[...] Among the birds, the fight is usually more peaceful. All those who have taken care of the matter believe that there is a profound rivalry among the males of many species to attract by chanting the females. Guayana's rough tordo, the birds of paradise and some others gather, and the males, successively, unfold their magnificent plumages and perform strange movements before the females who, placed as spectators, finally choose the most attractive companion.
Darwin 1859:136-137

In his book The Descent of Man he described numerous examples, such as the peacock's tail and the lion's mane. Darwin argued that competition between males is the result of selection for traits that increase the mating success of competing males, traits that might, however, decrease the individual's chances of survival. Indeed, bright colors make animals more visible to predators, the long plumage of male peacocks and birds of paradise, or the massive antlers of deer are uncomfortable burdens at best. Darwin knew that natural selection could not be expected to favor the evolution of such clearly disadvantageous traits, and he proposed that they arose through sexual selection,

which depends not on a struggle for existence in relation to other organic beings or external conditions, but on a struggle between individuals of one sex, usually males, for the possession of the other sex. Darwin, 1871.

For Darwin, sexual selection basically included two phenomena: the preference of females for certain males ―intersexual selection, female, or epigamic >― and, in polygamous species, the battles of males for the largest harem ―intrasexual selection―. In the latter case, large body size and musculature provide advantages in combat, while in the former, it is other male traits such as colorful plumage and complex courtship behavior that are selected for in order to increase the attention of males. the females. Darwin's ideas in this regard were not widely accepted, and proponents of the synthetic theory (Dobzhansky, Mayr, and Huxley) largely ignored the concept of sexual selection.^{[citation needed]< /sup>}

The study of sexual selection only gained momentum in the post-synthesis era. It has been argued that, as Wallace proposed, males with brilliant plumage thereby demonstrate their good health and high quality as sexual partners. According to this "sexual selection of good genes" hypothesis, male mate choice by females offers an evolutionary advantage. This view has received empirical support in recent decades. For example, an association, albeit small, has been found between offspring survival and male secondary sexual characters in a large number of taxa, such as birds, amphibians, fish, and insects.) In addition, research with blackbirds has provided the first empirical evidence that there is a correlation between a secondary sexual character and a trait that increases survival since males with the brightest colors have a stronger immune system. Thus, female selection could promote the general health of populations in this species. These and other data are consistent with the concept that female choice influences male traits and may even be beneficial to the species in ways that are not directly related to mating success.

One of the earliest references to animal cooperation comes from Charles Darwin, who pointed it out as a potential problem for his theory of natural selection. Since the publication of Origin of Species, others Authors have argued that altruistic behavior—selfless acts performed for the benefit of others—is incompatible with the principle of natural selection, despite the fact that examples of altruistic behavior such as parental care of young and mutualism, occur throughout the animal kingdom, from invertebrates to mammals.

Insects eusocial

For most of the 19th century, intellectuals such as Thomas Henry Huxley and Peter Kropotkin fervently debated whether animals cooperate and display altruistic behaviors. In 1902, Kropotkin offered an alternative view of human and animal survival in his book Mutual Support, where he stated that partnership offers the best development prospects for species. Kropotkin coined the term progressive evolution to describe how mutual aid became the sine qua non condition of all social, animal, and human life.

One of the most notorious forms of altruism occurs in certain eusocial insects, such as ants, bees, and wasps, which have a class of sterile female workers. The answer to the general question of the evolution of altruism, of the sociability of certain insects or of the existence of worker bees or ants that do not leave descendants comes from the inclusive fitness theory, also called family selection theory< /i>. According to the Darwin/Wallace principle, natural selection acts on differences in the reproductive success (ER) of each individual, where ER is the number of living offspring produced by that individual during a lifetime. Hamilton (1972) extended this idea to include the ER effects of the individual's relatives: inclusive fitness is the ER of each individual, plus the ER of their relatives, each devalued by the corresponding degree of relatedness. Numerous studies in a wide variety of animal species have shown that altruism is not in conflict with evolutionary theory. For this reason, it is necessary to modify and expand the traditional view that selection operates on a single isolated organism in a population: the isolated individual no longer seems to be of central importance from an evolutionary point of view, but rather as part of a a complex family network.

Macro Evolution, Promising Monsters, and Punctuated Balance

Main articles: Promising monster and Scored balance.

When macroevolution is defined as the process responsible for the emergence of higher-ranking taxa, metaphorical language is being used. In a strict sense, only new species "emerge", since the species is the only taxon that has ontological status. Macroevolution accounts for the emergence of important morphological discontinuities between groups of species, which is why they are classified as groups. markedly differentiated, that is, they belong to different and high-ranking taxonomic units. It is in the mechanisms that explain the emergence of these discontinuities that the different conceptions and disciplinary approaches are opposed.^{[citation required]}

Graphical representation of the conceptual differences between gradualism and the marked balance in relation to morphological divergence over time.

Gradualism is the orthodox macroevolutionary model. He explains macroevolution as the product of slow change, the accumulation of many small changes over time. This gradual change should be reflected in the fossil record with the appearance of numerous transitional forms between groups of organisms. However, the record is not abundant in intermediate forms. The gradualists attribute this discrepancy between their model and the found evidence to the imperfection of the geological record itself—according to Darwin, the geological record is a narrative from which volumes and many pages have been lost. The punctuated equilibrium model, proposed in 1972 by N. Eldredge and S. J. Gould, instead holds that the fossil record is a true reflection of what actually happened. Species appear suddenly in geological strata, are found there for 5 to 10 million years without major morphological changes, and then abruptly disappear from the record, replaced by another related but distinct species. Eldredge and Gould use the terms stasis and interruption, respectively, to designate these periods. According to his model, the abrupt interruptions in the fossil record of a species would reflect the moment in which it was replaced by a small peripheral population ―in which the rate of evolution would have been faster― that competed with the original species and ended up replacing it.. According to this pattern, natural selection operates not only within populations, but also between species, and qualitatively important changes in organisms would occur over relatively short geologic periods separated by long equilibration periods.^{[ citation required]}

In evolutionary biology, a promising monster is an organism with a deeply mutant phenotype that has the potential to establish a new evolutionary lineage. The term is used to describe a saltational speciation event that may be the origin of new groups of organisms. The phrase was coined by the German geneticist Richard Goldschmidt, who thought that the small, gradual changes that give rise to microevolution cannot explain macroevolution. The evolutionary relevance of the promising monsters has been rejected or questioned by many scientists who advocate the Synthetic Theory of Biological Evolution. In his work The material basis of evolution (The material basis of evolution), Goldschmidt wrote that "the change from one species to another is not a change that does not imply more and more atomistic changes, but a complete modification of the main pattern or main reaction system into a new one, which, later, can again produce intraspecific variation by means of micromutations".

Goldschmidt's thesis was universally rejected and widely ridiculed within the scientific community, which favored the neo-Darwinian explanations of R. A. Fisher, J. B. S. Haldane, and Sewall Wright.

Nevertheless, several lines of evidence suggest that promising monsters play a significant role in the origin of key innovations and novel body plans by saltational evolution, rather than gradual evolution. Stephen Jay Gould argued in 1977 that genes or regulatory sequences offered some support for Goldschmidt's postulates. In fact, he argued that examples of rapid evolution do not undermine Darwinism—as Goldschmidt supposed—but neither do they deserve immediate discredit, as many neo-Darwinists thought. Gould insisted that Charles Darwin's belief in gradualism was never a component essential part of his theory of evolution by natural selection. Thomas Henry Huxley also warned Darwin that he had burdened his work with unnecessary difficulty by unreservedly adopting the principle Natura non facit saltum. Huxley feared that such an assumption might discourage those naturalists who believed that cataclysms and the great evolutionary leaps played a significant role in the history of life. In this sense, Gould wrote:

As a Darwinist, I want to defend the Goldschmidt postulate that the macroevolution is not simply the extrapolated microevolution and that large structural transitions can occur quickly without a smooth series of intermediate states... In his 1940 book, Goldschmidt specifically invokes genes for development as potential manufacturers of promising monsters.

The synthesis of developmental biology and the theory of evolution

Genes HOX in mice

Although Darwin discussed developmental biology—formerly called embryology—in detail, this branch of biology did not contribute to the evolutionary synthesis. Ernst Mayr, in his essay What was the evolutionary synthesis? ("What was the evolutionary synthesis?"), explained that several of the embryologists of the period in which the modern synthesis arose had a position contrary to evolutionary theory:

"The representatives of some biological disciplines, for example, of the biology of development, offered strong resistance to synthesis. They were not left out of synthesis, as some of them now claim, they simply did not want to join."

In the past two decades, however, developmental biology and evolutionary biology have merged to form a new branch of biological research called Evolutionary Developmental Biology, or colloquially "Evo-devo," which explores how developmental processes have evolved and how the organization of the various parts of the body of ancient and present organisms has emerged.

The main discovery responsible for the integration of developmental biology with the theory of evolution was that of a group of regulatory genes, the family of homeotic genes (HOX genes). These genes encode DNA-binding proteins (transcription factors) that profoundly influence embryonic development. For example, the suppression of insect abdominal limbs is determined by functional changes in a protein called Ultrabithorax, which is encoded by a Hox gene. The Hox gene family exists in arthropods (insects, crustaceans, chelicerates, myriapods), chordates (fish, amphibians, reptiles, birds, mammals), and there are analogs among plant and fungal species. HOX genes influence the morphogenesis of vertebrate embryos by being expressed in different regions along the anteroposterior axis of the body. This family of genes is both functionally and structurally homologous to the homeotic complex (HOM-C) of Drosophila melanogaster. Based on the comparison of genes from various taxa, it has been possible to reconstruct the evolution of HOX gene clusters in vertebrates. The 39 genes that comprise the HOX gene family in humans and mice, for example, are organized into four genomic complexes located on different chromosomes, HOXA on the short arm of chromosome 7, HOXB on chromosome 17, HOXC on chromosome 12, and HOXD on the short arm of chromosome 7. 2, and each of them comprises 9 to 11 genes arranged in a sequence homologous to that of the D genome. melanogaster. Although the common ancestor of the mouse and human lived around 75 million years ago, the distribution and architecture of their HOX genes are identical. Thus, the HOX gene family is very old and apparently highly conserved, which has profound implications for the evolution of development patterns and processes.

Microbiology and horizontal gene transfer

Main article: Horizontal transfer of genes

Early evolutionary theories virtually ignored microbiology, due to the paucity of morphological traits and the lack of a species concept particularly among prokaryotes. Recent advances in the study of microbial genomics have contributed to a better understanding of microbial physiology. and ecology of these organisms and to facilitate research into their taxonomy and evolution. These studies have revealed totally unexpected levels of diversity among microbes.

Particularly important was the 1959 discovery in Japan of horizontal gene transfer. The exchange of genetic material between different species of bacteria has played a marked role in the spread of antibiotic resistance, and, at the dawn From a better knowledge of genomes, the theory has emerged that the importance of the horizontal transfer of genetic material in evolution is not limited to microorganisms, but reaches all living beings. Horizontal gene transfer in humans living beings occurs mainly through vehicles called mobile genetic elements or selfish genetic elements such as plasmids, transposons and viruses. Viruses can take up genetic material from one host and carry it to another. On the other hand, plasmids, circular DNA molecules that carry genes, can be exchanged between nearby bacteria, archaea, and yeasts; transposons, DNA sequences with a few genes, can be transferred horizontally between organisms living in symbiosis. Mainly operational genes (those involved in housekeeping) are transferred, while informational genes (those involved in transcription, translation and related processes) are rarely transferred horizontally. According to some estimates around 145 genes in the human genome they were acquired by horizontal transfer from other organisms. High levels of horizontal gene transfer have led to questions about the family tree of organisms: indeed, as part of the endosymbiotic theory of organelle origin, horizontal gene transfer genes was a critical step in the evolution of eukaryotes such as fungi, plants, and animals.

Endosymbiosis and the origin of eukaryotic cells

Main article: Eucariogenesis

Origin of sexual reproduction

According to the phagotrophic hypothesis, the loss of the cell wall that allowed phagocytosis could also have allowed sexual reproduction very early in the history of biological evolution, since there are no records of primitive asexual eukaryotes having existed. The cytoskeleton, molecular motors, and endomembrane system also facilitate sexual reproduction. This is how sexual reproduction evolved into the process it is today, that is, meiosis followed by fertilization; and gametes (the product of meiosis) are produced in the most primitive eukaryotes that exist today, the protists.

Among protists, cell fusion is relatively widespread; and most also have nuclear fusion and meiosis, while others, called agamic, do not, for example, the cercozoan alga Chlorarachnion and the haptophyte Reticulosphaera. From this it has been postulated that cell fusion could have developed without the original objective being sexual reproduction. For example, plasmodia, large multinucleated cells that occur among slime molds, have as their objective the search for food. An accidental nuclear fusion or a failure in mitosis would make a polyploid nucleus; for this reason it is believed that meiosis could have developed as a mechanism to repair these errors; since organisms need to replicate their genetic material efficiently and reliably. Thus, there could originally have been an intermediate phase with cell fusion and meiosis but no nuclear fusion. This is how the need to repair genetic damage is one of the main theories that explain the origin of sexual reproduction. Likewise, diploid individuals can repair a mutated section of their DNA through genetic recombination, since there are two copies of the gene in the cell, and one of them is supposed to remain undamaged. On the other hand, a mutation in a haploid individual is more likely to persist, since the DNA repair machinery has no way of knowing what the original undamaged sequence was. The most primitive form of sex might have been an organism with Damaged DNA replicating an undamaged strand from a similar organism to repair itself.

Another theory is that sexual reproduction originated from parasitic mobile genetic elements that exchange genetic material (ie: copies of their own genome) to transmit and propagate, such as transposons, plasmids, or viruses. In some organisms, sexual reproduction has been shown to enhance the spread of parasitic genetic elements (for example in yeast or filamentous fungi). Bacterial conjugation, a form of genetic exchange that some sources describe as sex, is not a form of reproduction. However, it supports the mobile genetic element theory, since it is propagated by one of those "mobile genes", the F plasmid. On the other hand, it has been suggested that the modern cell cycle, by which mitosis, meiosis, and sex occur in all eukaryotes, it evolved due to the balance struck by viruses, which characteristically follow a trade-off pattern between infecting as many hosts as possible and killing an individual host through viral proliferation. Hypothetically, viral replication cycles can mirror those of plasmids or transposons.

A third, less widely accepted theory says that sex might have evolved as a form of cannibalism. One primitive organism ate another, but instead of fully digesting it, some of the 'eaten' organism's DNA was eaten. would have been incorporated into the 'comedor' organism.

Variations in the expression of genes involved in heredity

Recent findings have confirmed important examples of heritable changes that cannot be explained by changes in the nucleotide sequence in DNA. These phenomena are classified as systems of epigenetic inheritance. Chromatin-marking DNA methylation, self-sustaining metabolic loops, gene silencing by RNA interference, and three-dimensional conformation of proteins (such as prions) are areas where studies have been reported. discovered systems of epigenetic inheritance at the organismal level. Developmental biologists suggest that complex interactions in genetic networks and communication between cells may lead to heritable variations that may underlie some of the mechanisms of phenotypic plasticity and channeling of development. Heritability can also occur at even larger scales. For example, ecological or extragenetic inheritance through the process of niche construction is defined by the regular and repeated activities of organisms in their environment. This generates a legacy of effects that modify and feed back the selection regime of subsequent generations. The descendants inherit genes plus the environmental characteristics generated by the ecological actions of the ancestors. Other examples of heritability in evolution that are not under the direct control of genes include the inheritance of cultural traits and symbiogenesis.

Other theories of evolution and scientific criticisms of the synthetic theory

Main article: Objections to the theory of evolution

Richard Dawkins, in his work The Selfish Gene of 1976, made the following statement:

Today the theory of evolution is as subject to doubt as the theory that the Earth revolves around the Sun.

Although biological evolution has been accepted as a fact since the 18th century, its scientific explanation has sparked much debate. The theory called modern evolutionary synthesis (or simply synthetic theory), is the model currently accepted by the scientific community to describe evolutionary phenomena; and although there is no solid alternative theory developed today, scientists such as Motō Kimura or Niles Eldredge and Stephen Jay Gould have claimed the need to reform, expand or replace the synthetic theory, with new models capable of integrating, for example, the biology of the developing or incorporating into current theory a series of biological discoveries whose evolutionary role is being debated; such as certain epigenetic hereditary mechanisms, horizontal gene transfer, or proposals such as the existence of multiple hierarchical levels of selection or the plausibility of genomic assimilation phenomena to explain macroevolutionary processes.

The most criticized and debated aspects of the modern evolutionary synthesis theory are: gradualism, which has obtained the Eldredge and Gould punctuated equilibrium model as an answer; the preponderance of natural selection over purely stochastic processes; the lack of a satisfactory explanation for altruistic behavior and genetic reductionism that would contradict the holistic characteristics and emergent properties inherent in any complex biological system. Despite what has been indicated, however, it must be considered that the current scientific consensus is that the theory itself (in its foundations) has not been refuted in the field of evolutionary biology, only being perfected; and for this reason it is still considered the "cornerstone of modern biology".

Other minority hypotheses

Main article: Symbinogenetic theory

Among other minority hypotheses, that of the American biologist Lynn Margulis stands out, who considered that, in the same way that eukaryotic cells arose through the symbiogenetic interaction of several prokaryotic cells, many other characteristics of organisms and the phenomenon of speciation were the consequence of similar symbiogenetic interactions. In her work Capturing Genomes. A theory of the origin of species Margulis argued that symbiogenesis is the main force in evolution. According to his theory, the acquisition and accumulation of random mutations are not enough to explain how heritable variations occur, and he postulated that organelles, organisms, and species arose as the result of symbiogenesis. While modern evolutionary synthesis does Emphasizing competition as the main force behind evolution, Margulis proposed that cooperation is the driver of evolutionary change. He argues that bacteria, along with other microorganisms, helped create the conditions required for life on Earth, such as a high oxygen concentration. Ella Margulis argued that these microorganisms are the main reason why current conditions are maintained. She also affirmed that bacteria are capable of exchanging genes more quickly and easily than eukaryotes, and because of this they are more versatile and the architects of the complexity of living beings.

Similarly, Máximo Sandín vehemently rejected any of the versions of Darwinism present in current theory and proposed an alternative hypothesis to explain evolution. In the first place, it appreciates the work of Lamarck, and suggests that the hypotheses or predictions, known as Lamarckism, made by this biologist are corroborated by the facts. For example, Sandín formulated his hypothesis based on the observation that the Environmental circumstances can condition not only the expression of genetic information (epigenetic phenomena, alternative splicing control, genomic stress...), but also the dynamics of the embryonic development process, and postulated that the fundamental foundation of ecosystems is equilibrium and not competition. According to his ideas, one can appreciate the tendency of organic forms to greater complexity, as a consequence of some laws that govern the variability of organisms, and that are, in some way, inscribed in organisms. Considering that 98.5% of the human genome, for example, is made up of repeated sequences with a regulatory function, as well as a notable amount of endogenous viruses, Sandín concludes that this conformation of the genome cannot be the result of chance and natural selection and which is produced instead by environmental pressure, which causes certain viruses to be inserted into the genome or certain gene sequences to be modified and, as a consequence, completely new organisms are generated, with substantial differences with respect to their predecessors. According to this theory, which rejects Dawkins' "selfish DNA" thesis, the fundamental mechanism of evolutionary change is only the ability of viruses to integrate into already existing genomes through the horizontal transfer of their genes. In addition, Sandín believes that the environment, and not random mutations, is the cause of certain groups of living beings assuming new characteristics, not gradually, but in specific episodes and without intermediate phases. According to the philosopher Maurício Abdalla, the hypothesis supported by Sandín is supported by a large amount of scientific data and opens a new area of research in the field of biology.

Experiments and studies on the evolutionary process

Main article: Pilot biological developments

Direct observation of the evolutionary process in bacteria

Richard Lenski, a professor at Michigan State University, began an experiment in 1989 to study the evolution of bacteria, fostered by the rapid reproduction of these microorganisms. Lenski established several subcultures from a strain of Escherichia coli, with the aim of observing if there were any differences between the original bacteria and their descendants. The different cultures were kept in stable conditions and every seventy-five days —approximately five hundred generations— the researchers extracted a sample from each of them and frozen it, proceeding in the same way for the subcultures of these subcultures. By 2010, the experiment covered some fifty thousand generations of bacteria.^{[citation needed]}

After ten thousand generations, the bacteria already showed quite a few differences from the ancestral strain. The new bacteria were larger and divided much faster in the DM culture medium used for the experiment. The most striking change was that in one of the subcultures in generation 31,500, the bacteria began to consume the citrate present in the DM medium and that E. coli is not normally capable of metabolizing. Therefore, the bacteria in that subculture evolved to adapt and grow better in the conditions of their environment. Another important evolutionary change occurred after twenty thousand generations: the bacteria in a second subculture experienced a change in their mutation rate, causing a accumulation of mutations in its genome (hypermutable phenotype). Being a culture in a constant environment, most of the new mutations were neutral, but an increase in beneficial mutations was also observed in the descendants of this subculture.

Lenski's results led to the establishment of other similar experiments, but with different temperature conditions and power sources, with the presence of antibiotics. Different microorganisms were also investigated: Pseudomonas fluorescens, Myxococcus xanthus, and even yeasts. Similar results were found in all of them: the microorganisms changed, evolved and adapted to the culture conditions.^{[citation needed]}

Computer simulation of the process of biological evolution

With few exceptions, biological evolution is too slow a process to be directly observed. For this reason, disciplines such as Paleontology, Evolutionary Biology or Phylogeny are used, among other areas, for the observation and indirect study of evolution. Since the last decade of the XX century, the development of bioinformatics has led to the use of computer tools for the study of various aspects of the evolutionary process.

One of the applications of computer tools to the study of evolution consists of the in silico simulation of the evolutionary process, using digital organisms, a series of programs that use the resources available in the processor to survive and reproduce. An example of this application is the Earth program, developed in 1990 by ecologist Thomas Ray for the study of evolution and ecology. Similar tools are used to investigate the evolutionary basis of behaviors such as altruism, mutation rates, and population genetics.^{[citation needed]}

Social and cultural reactions

Main article: Objections to the theory of evolution

As Darwinism achieved wide acceptance in the 1870s, Charles Darwin's caricatures were made with a body of ape or monkey as a form of argument ad hominem to discredit the theory of evolution.

In the 19th century, especially after the publication of The Origin of Species, the idea that life had evolved was a topic of intense academic debate focused on the philosophical, social, and religious implications of evolution. Today, the fact that organisms evolve is undisputed in the scientific literature, and the modern evolutionary synthesis is widely accepted among scientists. However, evolution remains a controversial concept among religious groups. Biologists Evolutionists have continued to study various aspects of evolution by formulating hypotheses as well as constructing theories based on evidence from the field or laboratory and on data generated by the methods of mathematical and theoretical biology. His discoveries have influenced not only the development of biology, but many other scientific and industrial fields, including agriculture, medicine, and computing.

The progressive increase in the knowledge of evolutionary phenomena has resulted in the revision, rejection or, at least, the questioning of the traditional creationist and fixist explanations of some religious and mystical positions and, in fact, some concepts, such as descent from a common ancestor, still arouse rejection in some people, who believe that evolution contradicts the creation myth in their religion. As recognized by Darwin himself, the most controversial implications of evolution evolutionary biology concerns the origins of man. In some countries—notably the United States—this tension between science and religion has fueled the creation–evolution controversy, a continuing religious conflict centered on politics and public education..While other fields of science, such as cosmology, and Earth sciences, are also contradicted by literal interpretations of many texts s, evolutionary biology encounters significantly greater opposition from many religious believers.^{[citation needed]}

The most important impact of evolutionary theory occurs at the level of the history of modern thought and its relationship with society, due to the non-teleological nature of evolutionary mechanisms: evolution does not follow an end or objective. Structures and species do not "appear" out of necessity or by divine design, but from the variety of existing forms, only the most adapted are preserved over time. This "blind" mechanism, independent of a plan, of a divine will or of a supernatural force has consequently been explored in other branches of knowledge.^{[citation needed]}

See also: Social effects of the theory of evolution

Evolution and politics

The adoption of the evolutionary perspective to address problems in other fields has been enriching and very current; however, in the process there have also been abuses ―attributing a biological value to cultural and cognitive differences― or distortions of it ―as justification for eugenic positions― which have been used as «Argumentum ad consequentiam» through the history of objections to the theory of evolution.

For example, Francis Galton used eugenic arguments to promote policies to enhance the human gene pool, such as incentives for reproduction of those with "good" genes, and forced sterilization, prenatal testing, contraception, and even the removal of people with "bad" genes. Another example of this use of evolutionary theory is Social Darwinism, conceived by Herbert Spencer, which popularized the term "survival of the fittest" and which was used to justify sexism, imperialism, social inequality, racial superiority (which helped inspire Nazi ideology) as inevitable consequences of natural laws. Social Darwinism was used in the United States to argue for restricting immigration or to enact state laws requiring sterilization of 'mentally defectives'. However, Darwin himself rejected several of these ideas, and scientists and philosophers contest These ideas are considered by contemporaries to be neither implicit in evolutionary theory nor supported by available data.

On the other hand, the philosophers Karl Marx and Friedrich Engels saw Darwin's new biological understanding of evolution by natural selection as essential to the new interpretation of scientific socialism, since according to Marx, it provides a &# 34;base in the natural sciences for the class struggle in history". Marx himself considered himself an admirer of Darwin and quoted him several times in his works. In Capital, which I gave him a copy of, he concluded that "a history of technology must be written like the one Darwin has written in the natural world on the formation of animal and vegetable organs." Engels argued in The role of labor in the transformation from ape to man that the application of labor implements played a decisive role in differentiating man from the animal world; of the social evolution of Lewis H. Morgan in his work The origin of the family, private property and the state. According to Alexander Vucinich, "Engels gave Marx credit for extending Darwin's theory to the study of internal dynamics and change in human society." In the 1890s, Piotr Kropotkin published The mutual support as an anarcho-communist response to social Darwinism and in particular to the essay of the xix century «The struggle for existence» by Thomas H. Huxley.

The conflict between making Marxist theory and Darwinism compatible continued throughout the 20th century. Evolutionary biologist J. B. S. Haldane, one of the leading contributors to modern Darwinism with a communist, stated, "I believe that Marxism is true." In Materialism and Empirio-Criticism , Lenin argued for convergence of the laws of evolution of economic policy (Marx), of biology (Charles Darwin) and of physics (Hermann von Helmholtz). On the other hand, Karl Kautsky promoted the future image of the "new man" through social and eugenic instruments. Lamarckism remained in the Soviet Union labeled as "creative Soviet Darwinism"; until 1965. Meanwhile, on the other hand, Lysenkoism was officially promoted as a supposedly scientific doctrine (in keeping with the fact that in 1948, five years before Joseph Stalin's death, genetics was officially declared a "bourgeois pseudoscience"). ”).

In A Darwinian Left, philosopher Peter Singer argues that the view of human nature provided by evolutionary science, particularly evolutionary psychology, is compatible with the left's ideological framework and should join him.

Evolution and religion

Main articles: Creationism, Smart design and Theist revolution.

Religious differences on the issue of evolution in the United States (2007) Percentage that believe evolution is the best explanation of the origin of humanity
			%
Buddhists			81
Hindus			80
Jews			77
Not affiliated			72
Catholics			58
Orthodox			54
Protestants			51
Muslims			45
Black Church			38
Evangelicals			24
Mormons			22
Jehovah ' s Witnesses			8
Percentage of United States total population: 48% Source: Pew Forum

Before geology became a science, in the early 19th century, both Western religions and Scientists dogmatically and almost unanimously discounted or condemned any proposal that implied that life was the result of an evolutionary process. However, as geological evidence began to accumulate around the world, a group of scientists began to question whether these new discoveries could be reconciled with a literal interpretation of the creation account in the Judeo-Christian Bible. Some religious geologists, such as Dean William Auckland in England, Edward Hitchcock in the United States, and Hugh Miller in Scotland, continued to explain the geological and fossil evidence only in terms of a universal Flood; but once Charles Darwin published his Origin of Species in 1859, scientific opinion began to move rapidly away from biblical literalism. This early debate about the literal validity of the Bible was carried out in public, and destabilized educational opinion in Europe and America, even instigating a "counter-reformation" in the form of a religious revival on both continents between 1857 and 1860.

In countries or regions where the majority of the population holds strong religious beliefs, creationism has much greater appeal than in countries where the majority of people hold secular beliefs. From the 1920s to the present in the United States, various religious attacks on the teaching of evolutionary theory have occurred, particularly by evangelical or Pentecostal Christian fundamentalists. Despite the overwhelming evidence for the theory of evolution, the Biblical description of the creation of humans and each other species as separate and finished species by a divine being is considered true by some groups. This point of view is commonly called creationism, and continues to be held by some fundamentalist religious groups, particularly American Protestants; primarily through a form of creationism called "intelligent design."^{[citation needed]}

Evolution's opponents scored a victory in the "Scopes Monkey Trial" of 1925 when the Tennessee Legislature passed a law making it a crime to teach "any theory which denies the story of the Divine Creation of man as taught in the Bible." Meanwhile, in the late 1960s, the US Supreme Court issued severe restrictions on state governments that opposed the teaching of evolution. In 1968, in the Epperson v. Arkansas, the superior court struck down an Arkansas law that prohibited the teaching of evolution in public schools.

Religious-creationist lobbies want to exclude the teaching of biological evolution from public education in that country; Although it is now a rather local phenomenon, with basic science instruction being required within the curricula, polls reveal a great sensitivity of the American public to this message, which has no equivalent anywhere else in the world. Another of the best-known episodes of this confrontation occurred in 2005 in the trial that was held in a United States federal court against a school district in Dover, Pennsylvania, which demanded the explanation of intelligent design as an alternative to evolution. In that year the Kansas State Board of Education decided to allow creationist doctrines to be taught as an alternative to the scientific theory of evolution. This decision was followed by a strong public response., which had one of its best-known consequences in the creation of a parody of religion, Pastafarianism, an invention of Bobby Henderson, a Physics graduate from Oregon State University, to ironically demonstrate that it is inappropriate and wrong to teach intelligent design as a scientific theory. In the Kitzmiller v. Dover trial, Judge John E. Jones III ruled "ID (intelligent design) is nothing less than the progeny of creationism [...] a religious view, a mere relabeling of creationism and not a scientific theory" and concluded by declaring it "unconstitutional to teach ID as an alternative to evolution in a public school science classroom." The Kansas State Board of Education later reversed its decision in August 2006. This educational conflict has also affected other countries; for example, in 2005 in Italy there was an attempt to suspend the teaching of the theory of evolution.

In response to the scientific evidence of the theory of evolution, many religionists and philosophers have tried to unify the scientific and religious points of view, either formally or informally; through a “pro-evolutionary creationism”. Thus, for example, some religionists have adopted a creationist approach from theistic evolution or evolutionary creationism, and defend that God provides a divine spark that initiates the process of evolution, and (or) where God created the course of evolution.^[] Contemporary Christian Scientists who accept evolution include biologist Kenneth Miller and geneticist Francis Collins.

From 1950 the Catholic Church took a neutral position regarding evolution with the encyclical Humani generis of Pope Pius XII. In it he distinguished between the soul, as it was created by God, and the physical body, whose development can be the object of an empirical study:

... the Magisterium of the Church does not prohibit the one who, according to the current state of science and theology, in the research and disputes, among the most competent men in the fields, is subject to study the doctrine of evolutionism, as soon as it seeks the origin of the human body in a pre-existing living matter—but the Catholic faith commands to defend that souls are created immediately by God. But all this is to be done in such a way that the reasons for one and another opinion—that is, the defender and the contrary to evolutionism—will be examined and judged seriously, moderately and temporarily; and in such a way that everyone is willing to submit to the judgment of the Church, to whom Christ conferred the task of interpreting the Holy Scriptures authentically and defending the dogmas of faith.

On the other hand, the encyclical neither endorses nor rejects the general belief in evolution because the evidence was not considered convincing at the time. It allows, however, the possibility of accepting it in the future:

Not a few pray with insistence that the Catholic faith take such sciences very into account; and this is certainly worthy of praise, provided that it is actually proven facts; but it is necessary to walk with much caution when it is rather only a hypothesis, which, even supported by human science, pray with the doctrine contained in Sacred Scripture or in tradition.

In 1996, John Paul II affirmed that "the theory of evolution is more than a hypothesis" and recalled that "The Magisterium of the Church is directly interested in the question of evolution, because it influences the conception of man". Pope Benedict XVI has stated that "there is much scientific evidence in favor of evolution, which is presented as a reality that we must see and that enriches our knowledge of life and of being as such. But the doctrine of evolution does not answer all the questions and, above all, it does not answer the great philosophical question: where does all this come from and how does everything take a path that finally leads to man?» Other denominations such as the Assembly General of the Presbyterian Church declared that "there is no contradiction between an evolutionary theory of human origins and the doctrine of God as Creator." As for Judaism, the Central Conference of American Rabbis stated that "students' ignorance of evolution will seriously undermine their understanding of the world and the natural laws that govern it, and their introduction to other explanations described as 'scientific'. #39; it will give them false ideas about scientific methods and criteria."

Muslim reaction to the theory of evolution varied widely, from those who believed in a literal Qur'anic interpretation of creation, to many educated Muslims who subscribed to a version of theistic or guided evolution, in which the Qur'an reinforced rather than contradicted science. This latter reaction was encouraged because Al-Jahiz, a 9th-century Muslim scholar, had proposed a concept similar to that of natural selection. However, acceptance of evolution remains low in the Muslim world as figures Prominent scholars reject evolutionary theory as a denial of God and as unreliable in explaining the origin of humans. Other objections by Muslim scholars and writers largely mirror those raised in the Western world. On the other hand, the debate on Darwin's ideas did not generate significant controversy in countries such as China.

Regardless of their acceptance by mainstream religious hierarchies, the same initial objections to Darwin's theory continue to be used against current evolutionary theory. Ideas that species change over time through natural processes and that different species share ancestors appear to contradict the Genesis account of Creation. Believers in Biblical inerrancy attacked Darwinism as heresy. Natural theology of the 19th century was characterized by William Paley's watchmaker analogy, a design argument still used by the movement creationist. When Darwin's theory was published, ideas of theistic evolution were presented as indicating that evolution is a secondary cause open to scientific investigation, while maintaining belief in God as a primary cause, with an unspecified role. in the direction of evolution and in the creation of human beings.

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