Human evolution
| The road to Homo sapiens (The Progress of Progress) .jpg) |
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| Ancestors of Homo sapiens |
| Previous to gender Homo |
First Hominids
Australopithecus
Paranthropus
Kenyanthropus
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| Gender Homo |
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Human evolution or hominization is the process of biological evolution of the human species from its ancestors to the present day. The study of this process requires an interdisciplinary analysis in which knowledge is complemented from sciences such as genetics, physical anthropology, paleontology, stratigraphy, geochronology, archeology and linguistics.
The term human, in the context of its evolution, refers to individuals of the genus Homo. However, studies of human evolution include other hominins, such as Ardipithecus, Australopithecus, etc. Thus, the specific study of human evolution is the study of the lineage, or clade, which incorporates all species closer to modern humans than to the chimpanzee, the closest living relative. The molecular and paleontological evidence have made it possible to estimate that the common ancestor between Homo sapiens and Pan troglodytes lived in Africa between five and seven million years ago. From this divergence, new species continued to emerge within the hominin lineage, all of them currently extinct except for Homo sapiens.
Genetic aspects of evolution
When analyzing the current human genome, it has been discovered that in its evolutionary process there are several facts to highlight. Thus, it can be seen, for example, that Homo sapiens shares almost 99% of its genes with the chimpanzee and the bonobo. For greater precision, the genome of any individual of our species has a difference of only 1.24% with respect to the genome of Pan troglodytes (chimpanzees) and 1.62% with respect to the genome of gorillas.
Genomic analysis has established the following relationship:
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Introgression and hybridization
Based on the genetic analysis of human evolution, it is postulated that within its genealogy there would have been introgression on several occasions. An example of this is the oldest current Y chromosome (Y-chromosome A00), which would date back to archaic humans (approximately 340,000 years ago).
It also highlights the discovery of the existence of hybridization with other older hominid species, such as Homo neanderthalensis (from 1% to 4% of Neanderthal genes per person, mainly in Europe), and with the Denisovan hominid (local people living in Papua New Guinea today in Southeast Asia owe at least 3% of their genome per person to Denisovan hominins). that when analyzing the total percentage of Homo neanderthalensis DNA within the current non-African human population, this percentage increases significantly to 20%; this Neanderthal genome being related to genes that produced a "heterosis" to environmental adaptations (such as skin phenotypes), but also implicated in diseases such as type 2 diabetes, Crohn's disease, lupus, and biliary cirrhosis.
Human endogenous retroviruses
It also highlights that human endogenous retroviruses (HERV) (DNA sequence derived from viruses belonging to the group of retroviruses) comprise a significant part of the human genome. With approximately 98,000 ERV fragments and elements, these make up almost 8% of the current human genome, which humans have acquired at different time periods of their evolution.
Stages in the human evolutionary line
Pre-australopithecines
The first possible bipedal hominids (hominins) are Sahelanthropus tchadiensis (with an age of 7 million years and found in Chad, but which raises doubts about its affiliation to our evolutionary line), Orrorin tugenensis (about 6 million years old and found in East Africa) and Ardipithecus (between 5.5-4.5 million years old and found in the same region). Fossils of these hominids are few and fragmentary, and there is no general agreement as to whether they were fully bipedal. However, after the discovery of the almost complete skeleton of an individual of Ardipithecus ramidus nicknamed Ardi, some doubts have been resolved in this regard; thus, the shape of the upper part of the pelvis indicates that it was bipedal and that it walked with a straight back, but the shape of the foot, with the big toe directed inward (as on the hands) instead of being parallel to the others, indicates that he had to walk on the outside of his feet and that he could not cover great distances.
Australopithecines
The first hominids that are certain to have been fully bipedal are members of the genus Australopithecus, of which very complete skeletons have been preserved (such as that of the famous Lucy).
This type of hominin thrived in the woodlands of eastern Africa between 4 and 2.5 million years ago with remarkable ecological success, as evidenced by the radiation it experienced, with at least five different species spreading from Ethiopia and the Chad to South Africa.
Their disappearance has been attributed to the climate crisis that began about 2.8 million years ago and led to a desertification of the savannah with the consequent expansion of open, steppe ecosystems. As a result of this evolutionary pressure, some Australopithecus specialized in the exploitation of hard plant products with little nutritional value, developing an impressive chewing apparatus, giving rise to Paranthropus; Other Australopithecus gradually became more carnivorous, giving rise to the first Homo.
Early Homo
It is not known with certainty from which species the first members of the genus Homo came from; Australopithecus africanus, A. afarensis and A. garhi, but there is no general agreement. It has also been suggested that Kenyanthropus platyops may have been the ancestor of early Homo.
Classically, hominids capable of making stone tools are considered to belong to the genus Homo. However, this vision has been questioned; for example, it has been suggested that Australopithecus ghari was capable of making tools 2.5 million years ago. The first tools were very simple and fit into the Olduvayan or Mode 1 lithic industry. The oldest come from the Afar region (Ethiopia) and are estimated to be around 2.6 million years old, but there are no hominid fossils associated with them.
Two species have been described from this phase, Homo rudolfensis and Homo habilis, which inhabited East Africa between 2.5 and 1.8 million years ago, which sometimes they come together in one. The cranial volume of these species ranges from 650 to 800 cm³.
People of Eurasia
This is undoubtedly the most confusing and complex stage of human evolution. The chronological successor of the aforementioned Homo rudolfensis and Homo habilis is Homo ergaster, whose oldest fossils date from approximately 1.8 million years ago., and its cranial volume ranges between 850 and 880 cm³. Morphologically it is very similar to Homo erectus and is sometimes referred to as “African Homo erectus”. It is supposed that he was the first of our ancestors to leave Africa; Fossils similar to H. ergaster (or perhaps Homo habilis) in Dmanisi (Georgia), dated to 1.8 million years old and named Homo georgicus which prove the early departure from Africa of our remote ancestors.
This first human migration led to the differentiation of two lineages descended from Homo ergaster: Homo erectus in the Far East (China, Java) and Homo antecessor/ Homo cepranensis in Europe (Spain, Italy). For their part, the members of H. ergaster who remained in Africa invented a new, more elaborate mode of stone carving called the Acheulean or Mode 2 (1.6-1.7 million years ago). It has been speculated that the clans possessing the new technology would have occupied the most favorable environments, displacing the less technologically advanced ones, who were forced to emigrate. It is certainly surprising that H. antecessor and H. erectus continued to use primitive Mode 1 (Olduvayan), hundreds of thousands of years after the Acheulean discovery. An alternative explanation is that the migration occurred before the appearance of the Acheulean.
After the discovery of the remains of Denisovan man, it has been detected that between one million and 700,000 years ago there was a genetic flow from African to Asian and European populations. From the subsequent millennia, in addition to the emblematic fossils of Homo erectus found in Java and Peking, China, other hominin remains have been found, whose morphological characteristics present clear differences, as well as coincidences, both with H. erectus as with H. sapiens: those from Hathnora, Narmada Valley, India, about 250,000 years ago; the Dali skull, China, dating to 200,000 years ago; Jinniushan's wife; 106,000-year-old Zhirendong Jaw, 100,000-year-old Xuchang Skull; the Orsang Man (India), dating to 50,000 years ago; the Deer Cave Men of China, who lived up to 11,500 years ago; and the Solo Man (Java).
Under conditions of isolation, independent species evolved, such as Homo luzonensis; and Homo floresiensis from the Island of Flores (Indonesia), species that have disappeared for a long time. 60,000 years. Although they could have evolved from early populations of H. erectus, the proportions of the lower extremities, the bones of the feet and the functional anatomy of the wrist and shoulder, more similar to Homo Habilis and even Australopithecus, suggest that their ancestors left Africa before the evolution of H. erectus.
For its part, in Europe there is evidence of human presence for more than 1 million years (Homo antecessor), but older stone tools not associated with fossil remains have been found in various places. The central position of H. antecessor as the common ancestor of Homo neanderthalensis and Homo sapiens has been ruled out by the discoverers of the remains (Eudald Carbonell and Juan Luis Arsuaga).
The last representatives of this phase of our evolution are Homo heidelbergensis in Europe, which is supposedly in the evolutionary line of the Neanderthals, and Homo rhodesiensis in Africa, which would be the ancestor of modern man.
A more conservative view of this stage of human evolution reduces all the mentioned species to one, Homo erectus, which is considered a widely dispersed polytypic species with numerous subspecies and genetically interconnected interfertile populations.
New origins in Africa
The final phase of the evolution of the human species is presided over by three intelligent human species, who for a long period coexisted and competed for the same resources. These are Neanderthal Man (Homo neanderthalensis), the Denisovan hominid species and modern man (Homo sapiens). They are actually parallel stories that, at a certain moment, intersect.
Neanderthals arose and evolved in Europe and the Middle East around 230,000 years ago, showing clear adaptations to the cold climate of the time (short, strong build, broad nose).
Denisovans lived 40,000 years ago in the Altai Mountains and probably in other areas where Neanderthals and sapiens also lived. Mitochondrial DNA analysis indicates a common female ancestor with the other two species approximately one million years ago. Sequencing of its genome has revealed that it would have shared an ancestor with Neanderthals around 650,000 years ago and with modern humans 800 years ago. 000 years. An uncovered molar exhibits distinctly different morphological characteristics from those of Neanderthals and modern humans.
Fossils from Djebel Irhoud (Morocco) dating to 300,000 years ago and the Florisbad skull (Homo helmei), from Bloemfontein (South Africa), dated to 259,000 years before present, point to Homo sapiens.
Excavations in the Olorgesailie Basin in southern Kenya, dating from 295,000 to 320,000 years ago using argon-40/argon-39 and uranium series methods, found traces of hominin activity, who at these sites made prepared cores and points, mined iron-rich rocks for red pigment, and acquired stone tool materials from distances of 25 to 50 kilometers. These findings suggest that complex behaviors that characterize Homo sapiens were already being recorded since then.
The Kibish Men, especially Omo I, are considered the oldest fossils of Homo sapiens dating from about 200,000 years ago (Ethiopia). About 90,000 years ago they reached the Near East where he met the Neanderthal Man who was fleeing to the south of the glaciation that was beating down Europe. Homo sapiens continued its expansion and about 45,000 years ago it reached Western Europe (France); At the same time, the Neanderthal Man withdrew, pushed by H. sapiens, to the periphery of its area of distribution (Iberian Peninsula, high plateaus of Croatia), where it disappeared about 28,000 years ago.
Although H. neanderthalensis has often been considered a subspecies of Homo sapiens (H. sapiens neanderthalensis), complete mitochondrial genome analysis of fossil H. neanderthalensis suggest that the existing difference is sufficient to consider them as two different species, separated by 660,000 (± 140,000) years ago (see section "Classification" on Homo neanderthalensis).
It is almost certain that Neanderthals are not the direct ancestors of modern humans, but belong to a parallel evolutionary line also derived from Homo erectus/Homo ergaster through the link known as Homo heidelbergensis. Neanderthals coexisted with Homo sapiens and perhaps ended up extinct due to competition with our species. However, analysis of the nuclear genome points to a Neanderthal contribution to the gene pool of modern humans. Eurasians possess between 1 and 5% of archaic genes per person that can be attributed to hybridization of Homo sapiens with H. neanderthalensis.
As for the so-called Cro-Magnon man, he corresponds to the Western European populations of the current species Homo sapiens.
Homo sapiens
The closest living relatives to our species are the great apes: the gorilla, chimpanzee, bonobo, and orangutan. The oldest fossils of Homo sapiens are almost two hundred thousand years old and come from southern Ethiopia (Kibish formation of the Omo river), considered the cradle of humanity (see Men of Kibish).. These fossil remains are followed in antiquity by those of Homo sapiens idaltu, with about one hundred and sixty thousand years.
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Some molecular genetic data consistent with paleontological findings, maintain that all human beings descend from the same mitochondrial Eve or EM, this means that, according to mtDNA scans -which is only transmitted through mothers-, all of present-day humanity has a common ancestor who would have lived in northeast Africa, probably in Tanzania (given the greater genetic diversity there) between 150,000 and 230,000 years ago (see human mitochondrial DNA haplogroups).
Studies of the human Y chromosome haplogroups conclude that there is paternal ancestry that goes back to the chromosomal Adam, who would have lived in sub-Saharan Africa between 60,000 and 90,000 years ago.
Other indications derived from very recent research suggest that the already meager population of Homo sapiens about seventy-four thousand years ago was reduced to the brink of extinction when the Toba volcano erupted, according to the Theory of the Toba catastrophe, a volcano located on the island of Sumatra, whose eruption has left Lake Toba as a trace. Such an eruption-burst had a force 3000 times greater than the eruption of Mount Saint Helena in 1980. This meant that much of the planet was covered by clouds of volcanic ash that negatively affected the populations of various species including humans. According to this hypothesis called the Toba Catastrophe among the scientific community, the population of Homo sapiens (then all in Africa; the first migration out of Africa was around the year 70,000 BC) would have reduced to only about a thousand individuals. If this is true, it would mean that the 'pool' of the species would have been restricted in such a way that the genetic unity of the human species would have been enhanced.[citation required] Not everyone agrees with that dating. After analyzing the DNA of people from all regions of the world, geneticist Spencer Wells argues that all humans living today are descended from a single individual who lived in Africa some 60,000 years ago. All of the above demonstrates monogenism. of the human species and, consequently, ruled out polygenism, which served as an "argument" to racist theories.
In 2021 a possible new species of archaic human was discovered from a skull dated to about 146,000 years old discovered in Harbin, northeast China, in 1933 dating to at least 146,000 years ago years during the Middle Pleistocene. He was christened Homo longi (Traditional Chinese 龍人; Simplified Chinese 龙人; translated as Dragon Man). His analysis suggests that Homo sapiens is more closely related to him than to Homo neanderthalensis.
Prehistoric migrations of Homo sapiens
Along with archaeological findings, the main indicators of the expansion of the human being throughout the planet are mitochondrial DNA and the Y chromosome, which are characteristic of maternal and paternal lineal descent, respectively.
Humans would have already started leaving Africa some 90,000 years before the present; colonizing the Mediterranean Levant at that time (these fossil remains have been attributable to early Homo sapiens, but their actual relationship to modern humans is highly debatable).
Australia and New Guinea: the Wallace Line did not mean for Homo sapiens an insurmountable limit for access this region. The arrival of humans in Australia dates back about fifty thousand years when they were able to build rustic rafts or reed rafts to cross the strait that separated Sahul from the Sunda region.
Europe: it began to be colonized only about forty thousand years ago, it is assumed that for millennia the Syrian desert was an insurmountable barrier from Africa to Europe, so a migration would have been more feasible coast from the Eritrean coast to the Yemeni coast and from there to the Indian subcontinent. The expansion through Europe coincides with the extinction of its contemporary at that time, the Neanderthal man.
Oceania: the colonization of these islands closest to Eurasia would have begun about fifty thousand years ago, but the expansion through this MUG (macro-geographical unit) was very slow and gradual, and about 50,000 years ago. About five thousand years ago, Austronesian peoples began an effective expansion through Oceania, although archipelagoes such as Hawaii and New Zealand were not yet populated by humans two thousand or fifteen hundred years ago (this required the development of appropriate naval technique and sufficient knowledge of nautical).
America: the arrival of man in America would have started some twenty thousand or at least fifteen thousand years ago, although there is no consensus on this. During the glaciations the level of the oceans descends to the degree that the "Old World" and the "New World" They form a megacontinent linked by the Beringian Bridge.
Evolutionary changes
Morphological aspects
Differences from other primates
When the ancestors of Homo sapiens and many other primates lived in jungles eating fruits, berries and leaves, abundant in vitamin C, they were able to lose the genetic capacity, which most animals have, to synthesize in your own body such a vitamin. Such losses during evolution have implied subtle but important determinations: when the original forests were reduced or, due to population growth, they became overcrowded, the primitive hominins (and later humans) were forced to travel great distances, to migrate, to obtain new sources. of nutrients (for example of the aforementioned vitamin C).
All the changes described have occurred in a relatively short period (although measured in millions of years), this explains the susceptibility of our species to conditions in the spine and in the blood and lymphatic circulation.
Cerebration
Cerebration and corticalization are topics that require articles of their own, given the scope and importance of these processes. Here it is important to comment on the minimum essential to understand human evolution.
Cerebration as well as corticalization are biological phenomena long before the appearance of hominids, however in these, and especially in Homo sapiens, cerebration and corticalization acquire a superlative degree (to the point that Teilhard de Chardin enunciated a curious theory, that of the noosphere and noogenesis, that is: theory of intelligent thinking, which is based on the evolution of the brain).
The Homo sapiens brain, relative to body mass, is one of the largest. More striking is the consumption of metabolic energy (for example, that produced by the "combustion" of glucose) required by the brain: 20% of all body energy, and even when the length of the intestines humans show the problems that arise.
In Homo sapiens the volume ranges from 1200 to 1400 cm³, the current global average is 1350 cm³; However, an increase in volume is not enough, but how it is arranged; that is: how the "structure" of the central nervous system and of the brain in particular. On average, Homo neanderthalensis could have had a larger brain than our species, but the morphology of their skulls shows that their brain structure was very different: with a scant forehead, Neanderthals had underdeveloped frontal lobes and, especially, very underdeveloped prefrontal cortex. The Homo sapiens skull not only has a prominent forehead but is also higher at the occiput (highly domed skull), this allows for the development of the frontal lobes. Of all the mammals, Homo sapiens is the only one whose face is located under the frontal lobes.
However, even more important for the evolution of the brain seem to have been mutations in the positioning of the sphenoid.
Mention has been made in the section dedicated to the appearance of articulated language of the importance of the FOXP2 gene; This gene is responsible for the development of the language areas and the synthesis areas (the synthesis areas are found in the cerebral cortex of the frontal lobes). The increase in the brain and its specialization allowed the appearance of the so-called lateralization, that is, a very important difference between the left hemisphere and the right hemisphere of the brain. The left hemisphere has specific areas developed in its cortex that enable symbolic language based on acoustic signifiers: Wernicke's area and Broca's area.
It is almost certain that 200,000 years ago the subjects of the species Homo sapiens had an intellectual potential equivalent to that of today, but it took millennia for this potential to be activated: the first record of Known artistic behavior dates back only about 75,000 years, the first graphics and purely symbolic expressions outside of spoken language date back only between 40,000 and 35,000 years ago. The first writings ("second memory" as Roland Barthes called them) date from between 5,500 or 5,000 years ago, in the Nile Valley or in Asian Mesopotamia.
It has been said, also lines before, that Homo sapiens maintains "primitive" since they are reminiscent of those of a child chimpanzee; in fact, such morphology is what allows to have the forehead on the face and the frontal lobes developed.
The head of Homo sapiens, to contain such a brain, is very large; even in the fetus and neonate, the main reason why deliveries are difficult, added to the disposition of the pelvis.
A partial solution to this is heterochrony: the human neonate is very incompletely developed at the time of delivery; It can be said (with some metaphor) that gestation in humans is not restricted to the already prolonged nine intrauterine months, but rather extends extrauterinely until at least the first four years; in fact, the infant is completely helpless for years, so much so that between the ages of 2 and 4 is when the visual areas of the brain are sufficiently developed to have a visual perception of their own being (Mirror stage discovered by Jacques Lacan in the 1930s). Now, if Homo sapiens takes a long time to be able to have a full perception of its body image, it is interesting to know that it is one of the few animals that perceives itself by seeing its reflected image (this capacity is only noticeable in bonobos, chimpanzees, and perhaps gorillas, orangutans, dolphins, and elephants).
Such is the prematureness of Homo sapiens, that while a newborn chimpanzee has a brain capacity of 65% of that of an adult chimpanzee, or the capacity of Australopithecus afarensis was at birth 50% compared to their adulthood, in Homo sapiens 'baby' such capacity does not exceed 25% of the capacity it will have at 45 years of age[citation required] (approximately 45 years is when the human brain fully develops[citation required]).
But the chronological development is not enough. For the human brain to "unfold" -so to speak- or develop requires stimulation and affection; otherwise the organization of some of the brain areas may become atrophied.
Standing
The Hominins, bipedal primates, would have emerged about 6 or 7 million years ago in Africa, when that continent was affected by a progressive desiccation that reduced the areas of forests and jungles. From this, the first and most accepted theory is that primates capable of walking easily in a bipedal way and standing upright appeared as an adaptation to the savannah biome (East Side Story;). Furthermore, in a warm environment with strong ultraviolet and infrared radiation, some of the best adaptive solutions are bipedal gait and the progressive reduction of the hairy layer, which prevents excessive overheating of the body. 150,000 years ago, North Africa once again suffered intense desertification, which meant another great evolutionary pressure to establish the main features of the species Homo sapiens.
However, there is currently a discrepancy regarding the theory of the appearance of bipedalism as a product of adaptation to life in the Savannah. The existence of fossil remains such as those of the genus Ardipithecus, with a shape of the toes and a pelvic structure that suggest that they walked upright, and the subsequent discovery of the fossil remains of Danuvius guggenmosi, raises a problem with this theory; and leads to the theory that bipedalism could have originated in the ancestors of the human being while they still moved over the trees.
In order to achieve the upright posture and gait, important modifications had to appear:
- Cráneo. To allow for bipedestation, the magnum foramen (or occipital orifice by which the spinal cord passes from the skull to the raquis) has moved; while in the apes the magnum foramen is located in the back of the skull, in the back of the skull, Homo sapiens (and in its direct ancestors) the magnun foramen has "displaced" almost to the base of it.
- Spinal column. The spine quite rectiline in apes, in the Homo sapiens and in its bipedal ancestors it has acquired curvatures that allow to better support the weight of the upper body. Such curvatures have a "resort" effect. Moreover, the spine has been able to erect almost 90° at the pelvis level; if compared to a chimpanzee it is noted that by lacking this primate of the lumbar curve, its body is pushed forward by its own weight. In human rakes the center of gravity has moved, so that the center of gravity of the whole body is placed above the support that constitutes the feet; having the Homo sapiens a relatively large head, the body gravity center is quite unstable. Human vertebrae are more circular than apes; this allows them to bear the vertical weight better.
- Pelvis. The pelvis must have widened, which has been fundamental in the evolution of our species. The illic bones of the pelvic region in the Homo sapiens (and immediate predecessors) "giran" into the pelvis. This allows you to better support the weight of the organs by being in an erect position. This modification implies a significant decrease in the possible speed of the race by humans. Bipedestation implies a position of the pelvis that makes the babies born "prematures": in fact, human childbirth is called a blindfold because there is almost a straight angle between the abdominal cavity and the vagina that in the pubis of the woman is almost frontal. If in all other mammals the so-called delivery channel is very brief, instead in females Homo sapiens It is very long and sinuous. This makes lightening difficult. This has been fundamental in the evolution of our species.
- Piernas. Also for bipedestation there have been other very important and evident morphological changes, particularly in members and joints. The lower limbs have been strengthened, the human femur bends inward, so that it allows the march without having to rotate almost the whole body; the joint of the knee has become almost omnidirectional (that is, it can move in various directions), although in the monkeys - for example the chimpanzee - there is a greater flexibility of the joint of the knee, which facilitates a better displacement by the next human cups, so that the next pairs is not
- Feet. In humans the feet have elongated, particularly in the heel, slightly reducing the fingers of the foot and leaving the "pulgar" of the foot (the elder finger), in general the foot has almost totally lost the apprehension capacity. It is known, in fact, that the human foot has ceased to be able to cling (what if it were a hand) to the branches, instead going to have an important function in the support of the whole body. The elder finger of the foot has a vital function to achieve the balance of the hominins during the march and the erect posture; in fact, the thumb of the foot of a chimpanzee is transversal, allowing the ape to cling more easily to the branches, instead the "pulging" of the human foot, by being aligned, facilitates the balance and momentum forward by going or running. The bones of the lower limbs are relatively rectangles compared to those of other primates.
Advantages and disadvantages of standing up
Clearly, the large number of anatomical modifications that led from quadrupedalism to bipedalism required strong selection pressure. There has been much discussion about the effectiveness and ineffectiveness of the bipedal gait compared to the quadrupedal one. It has also been noted that no other animal that adapted to the savannah at the end of the Miocene developed a bipedal gait.
If we take into account the theory that we start from hominids with a type of quadruped movement that is not very efficient for long journeys in open terrain, like the one presented by chimpanzees. The way in which chimpanzees move, supporting the second phalanx of their fingers, cannot be compared to the quadrupedal gait of any other mammal; On the other hand, the existence of a bipedal movement prior to inhabiting the sheet would have been an advantage in order to inhabit this environment.
As early savannah hominids, they were likely forced to travel considerable distances across open country to reach distant clumps of trees; the bipedal gait could be a very effective advantage in these conditions since:
- It allows to smell the horizon above the herbaceous vegetation in search of trees or predators.
- It allows you to transport things (such as food, sticks, stones or calves) with your hands, freed from the locomotive function.
- It is slower than the quadruped march, but it is less energetically costly, which should be interesting to travel long distances in the savannah, or in other poorer habitats in resources than the jungle.
- It exposes less surface to the sun and allows to take advantage of the breeze, which helps not to reheat the body and save water, useful in a habitat with a shortage of this resource.
Years ago it was argued that the liberation of the hands by the first bipedal hominids allowed them to make stone weapons for hunting; which would have been the main engine of our evolution. Today it is clear that the liberation of the hands (which occurred more than 4 million years ago) is not linked to the manufacture of tools, which happened about 2 million years later, and that the first hominins were not hunters and that at at most they ate carrion sporadically.[citation needed]
But bipedalism brought a disadvantage in reproduction, since the fact of going from quadrupedalism to bipedalism led to an anatomical change in the hips, with a great reduction of the birth canal that made delivery more difficult and painful, as described demonstrates when comparing the hip of an average chimpanzee with that of an Australopithecus such as Lucy, who also have a similar brain size.
Liberation of the upper limbs
The bipedal posture freed the upper limbs, which no longer have to perform the function of legs (except in very young children) nor that of brachiation, that is, moving from branch to branch with the arms, even when the The current human species, from the waist up, maintains a tree-like complexion.
This liberation of the upper limbs was, at first, an optimal adaptation to the savannah biome; by walking bipedally and with free arms, the ancestors of man could more easily gather their food; roots, fruits, leaves, insects, eggs, small reptiles, rodents and carrion; Indeed, many indications suggest that our ancestors were to a great extent scavengers and, within the scavenging, they practiced the modality called kleptoparasitism, that is, they stole the prey recently hunted by purely carnivorous species; For such a practice, our ancestors must have acted in bands, in an organized way.
The upper limbs, always in relation to other species, have been shortened. These upper limbs, being freed from locomotive functions, have been able to specialize in purely human functions. The opposable thumb is a characteristic inherited from the oldest primates, but if in these the main function has been to cling to the branches and secondly to apprehend the fruits or insects that served as food, in the evolutionary line that leads to our In this way, the motility of the hand, and in particular of its fingers, has gradually become more precise and delicate, which has facilitated the elaboration of artifacts; still (June 2005) there is no knowledge regarding the moment in which the evolutionary line began to create artifacts, it is certain that more than 2 million years ago Homo habilis/Homo rudolfensis made crude instruments that used assiduously (in any case, chimpanzees, in the wild, make very rudimentary "tools" of stone, wood and bone). The development of the ability to pronate in the wrist joint has also been extremely important for the ability to make artifacts.
Vision
Human inherits stereoscopic and panchromatic vision (the ability to see a wide range of colors in the visible spectrum) from prosimians; the eyes in the front part of the head allow stereoscopic vision (in three dimensions), but if this feature arises in prosimians as an adaptation to move better at night or in shady environments such as jungles, in Homo sapiens such a function takes on another value; it facilitates looking into the distance, scanning horizons, in this aspect vision is much sharper in humans than in other primates and prosimians. This will facilitate the fact that Homo sapiens is a highly visual being (for example, communications through mime), and will also facilitate the imaginary.
Specialization
Despite the set of morphological modifications outlined above, from the point of view of comparative anatomy, one issue stands out: Homo sapiens is a relatively unspecialized animal. Indeed, a large part of the animal species has achieved some type of anatomical specialization (for example, artiodactyls have hooves that allow them to run on cleared plains), but specializations, if they are usually an optimal adaptation to a certain biome, entail the risk of the disappearance of the specialized species associated with such a biome if it is modified.
The absence of such anatomical specializations has given humans an unusual adaptability among other vertebrate species to adapt to very diverse environmental conditions.
Furthermore, although it may seem paradoxical, Homo sapiens has neotenic characteristics. Indeed, the cranial structure of an adult Homo sapiens is closer to that of a baby chimpanzee than to that of an adult chimpanzee: the face is flattened ("orthognathous" or "low facial index") and the supraorbital torus is almost non-existent (in present-day humanity there are hardly any traces of torus in the so-called australoid populations). Otherwise it can be said that the browbones of Homo sapiens are "infantile", delicate, the face flattened or slightly prognathous.
Homo sapiens is, due to its anatomy, a very vulnerable animal if it is found in natural conditions.
Associated with the fact that, morphologically, human beings have characteristics that approximate those of a chimpanzee "child" is the 'orthognathism' and this means, among other things, that the teeth of Homo sapiens are relatively small and unspecialized, the jaws, for this reason, have been shortened and made more delicate, and the diastema or space in where the fangs fit. The weakness of human jaws makes them almost completely useless for biting defense against a predator, and they are also very deficient in being able to consume much of their food in their natural state, which is one of the many bodily deficits that lead to jaws. human to live in an organized society.
Cultural aspects
Emergence of symbolic language
Speaking of the appearance of human language, symbolic language, would logically seem to imply that we must first speak of cerebration, and that is quite true, but symbolic human language has its antecedents at times and morphological changes that precede major changes in the structure of the central nervous system. For example, chimpanzees can carry out a primary outline of symbolic language based on mime (in a similar way to a very simple system of mute communication).
Now, the symbolic language par excellence is the one based on acoustic signifiers, and for a species to have the capacity to articulate discrete sounds, more morphological innovations are required, some of them very probably prior to the development of a brain lo complex enough to think symbolically. Indeed, let's look at the oropharynx and the larynx: in mammals, with the exception of humans, the larynx is located in the upper part of the throat, so that the epiglottis closes the trachea tightly when drinking and eating food. In contrast, in Homo sapiens, the larynx is located lower down, which allows the vocal cords to produce more clearly differentiated and varied sounds, but by not being able to completely occlude the epiglottis, breathing and intake should be alternated so that the subject does not choke. The shortening of the prognathism that is compensated with an elevation of the palatal vault facilitates oral language. Another element of relevant importance is the position and structure of the hyoid bone, its gracefulness and motility will allow a sufficiently articulated oral language.
Studies carried out in the Sierra de Atapuerca (Spain) show that Homo antecessor, some 800,000 years ago, already had the capacity, at least in its vocal apparatus, to emit an oral language sufficiently articulated enough to be considered symbolic, although the customary manufacture of utensils (however crude they were) by Homo habilis some two million years ago, suggests that a very rudimentary articulated oral language already existed in them. but effective enough to transmit enough information or teaching for the making of the crude artifacts.
In addition to all the conditions just mentioned, essential for the appearance of a symbolic language, mention should be made of the appearance of the FOXP2 gene, which is basic for the possibility of such language and symbolic thought, as will be seen below.
Comparative table of the different species of the genus Homo
- The names in bold indicate the existence of numerous fossil records.
| Species | Chronology (cron) | Distribution | Adult height (m) | Adult mass (kg) | Cranial volume (cm3) | fossil record | Discovery / publication of the name |
|---|---|---|---|---|---|---|---|
| H. habilis | 2.5-1.4 | East Africa | 1.0-1.5 | 30-55 | 600 | Several | 1960/1964 |
| H. rudolfensis | 1.9 | Kenya | 1 skull | 1972/1986 | |||
| H. georgicus | 1.8-1.6 | Georgia | 600 | Few | 1999/02 | ||
| H. ergaster | 1.9–1.25 | East and South Africa | 1.7 | 80 | 700–850 | Several | 1975 |
| H. erectus | 2–0.3 | Africa, Eurasia (Java, China, Vietnam, Caucasus) | 1.8 | 60 | 900-1100 | Several | 1891/1892 |
| H. cepranensis | 0.8 | Italy | 1 cranial cup | 1994/2003 | |||
| H. predecessor | 0.8–0.35 | Spain, England | 1.60-1.85 | 60-85 | 1000 | Three places | 1994/1997 |
| H. heidelbergensis | 0.6–0.25 | Europe, Africa | 1.75-1.90 | 70-105 | 1100-1400 | Several | 1907/1908 |
| Homo rhodesiensis | 0.3–0.12 | Zambia | 1300 | Very few | 1921 | ||
| Homo neanderthalensis | 0.23–0.024 | Europe, Western Asia | 1.7 | 65–90 (strong) | 1200-1800 | Several | 1829/1864 |
| Homo sapiens | 0.32–present | World | 1.5-1.85 | 55-95 | 1000–1850 | She's still alive. | —/1758 |
| H. sapiens idaltu | 0.16 | Ethiopia | 1450 | 3 skulls | 1997/2003 | ||
| H. floriensis | 0.10–0.012 | Indonesia | 1.0.1 | 25 | 400 | 7 individuals | 2003/04 |
| H. lightensis | 0.22–0.019 | Philippines | 1.20 | 3 individuals | 2007/2019 |
Synoptic table of human evolution
| Época | Age | Time (absolute) | Australopitecinos (Africa) | Homo Africa | Homo in Europe | Homo in Asia | Culture |
|---|---|---|---|---|---|---|---|
| Holocene | (recent) | News 11 700 | H. sapiens | H. sapiens | H. sapiens | Neolithic at present (writing,...) | |
| Pleistocene | Tarantiense | 11 700 126 000 | H. sapiens | H. sapiens (40 000-act.) H. neanderthalensis (230 000-29 000) | H. sapiens (42 000-act.) H. floriensis (75 000-13 000) H. erectus soloensis (130 000-50 000) | Higher Paleolithic Musteriense (Abstract thought, art) | |
| Chibani | 129 000 774 000 | H. sapiens idaltu (185 000) H. sapiens (315 000-act.) H. rhodesiensis (600 000-160 000) | H. neanderthalensis (230 000-29 000) H. heidelbergensis (500 000-250 000) | H. erectus (1.8 Ma-250 000) | Musteriense Achelense (fire) | ||
| Calabriense | 781 000 1.8 Ma | Paranthropus robustus (2.0-1.2 Ma) P. boisei (2.3-1.3 Ma) Australopithecus sediba (1.95-1.78 Ma) | H. ergaster (1.75-1 Ma) H. habilis (1.9-1.6 Ma) | H. predecessor (purchase 780 000) H. cepranensis (800 000) Homo sp. of the Elephant Sima (1.2 Ma) | H. erectus (1.8 Ma-250 000) H. georgicus (1.8 Ma) | Achelense Olduvayense | |
| Gelasiense | 1.8 Ma 2.59 Ma | A. sediba (1.95-1.78 Ma) P. robustus (2.0-1.2 Ma) P. boisei (2.3-1.3 Ma) P. aethiopicus (2.6-2.2 Ma) A. garhi (2.5 Ma) A. africanus (3-2.5 Ma) | H. habilis (1.9-1.6 Ma) H. rudolfensis (2.4-1.9 Ma) | Olduvayense (Legal industry) | |||
| Plioceno | Piacenziense | 2.59 Ma 3.6 Ma | A. africanus (3-2.5 Ma)Kenyanthropus platyops (3.5 Ma) A. bahrelghazali (3.58 ± 0.27 Ma) A. afarensis (4-2.7 Ma) | ||||
| Zancliense | 3.6 Ma 5,33 Ma | A. afarensis (4-2.7 Ma) A. anamensis (4.2-3.9 Ma) |
Future of human evolution
Different possibilities have been hypothesized regarding the future evolution of the human being, among them:
A line of thought that ensures that the human species has stopped evolving in the same way as the rest of living beings, for different reasons.
- One of the reasons raised is that progress in science now allows to survive people who otherwise would have died (elimination or alteration of the natural selection process) as well as the existence of global mobility, thus diluting any genetic novelty in such a large population (elimination of genetic drift).
- On the other hand, Gregory Stock (UCLA), commented that "At present, traditional Darwinian evolution hardly produces any change in humans, and it is very unlikely that it will do so in the immediate future. The human population is too large and is too tangled, apart from the fact that selective pressures are too localized and transitory». Evolution accelerates when genetically similar members procreate with each other, but humanity is too large and too scattered for such concentration.
However, there are also other positions that consider that it is precisely technological advances that are currently driving human evolution, although in an artificial, non-Darwinian way. On the one hand, it has been proposed that the current environment favors the reproduction of intelligent people, regardless of their physical strength or state of health. Furthermore, it is possible that human genetic engineering allows selection of the genetic characteristics of the offspring.
On the other hand, it has also been proposed that in the future technology will enable people to live as cyborgs or even as digital beings within completely artificial bodies or structures.
Notes on Taxonomy
Taxonomy deals with the classification of organisms. Therefore, the definition of species is a fundamental aspect to classify specimens as belonging to different or the same species. In living organisms it is possible to define species under the criteria of the ability of different individuals to reproduce and have fertile offspring (definition of biological species). However, the fossil record poses more problems, since it is impossible to see the reproductive potential among extinct organisms. This makes defining species in paleontology extremely complex. An assumption to define and name species based on the fossil record is based on morphology; Under this premise, it is expected that there is greater morphological variation between species than between individuals of the same species.[citation required]
In the study of human evolution, defining and naming species is, as in any paleontological discipline, not only a scientific but also a psychological phenomenon. In this sense, we can divide paleontologists into two extremes according to the way they distinguish and define species in the fossil record: lumpers (lumpers) will try to define a few species, with greater inter-variation. -specific (i.e., within species), while splitters will define new species when there is a small morphological difference between specimens. Obviously these are two extremes of a phenomenon and most of paleontologists will fall somewhere in the middle.