Vestigiality
Vestigiality is the retention during the evolutionary process of genetically determined structures or attributes that have lost part or all of their ancestral function in a given species. Vestigiality assessment should generally be based on comparison with homologous features in related species. The appearance of vestiges occurs by normal evolutionary processes, usually by the loss of function of a trait that is no longer subject to positive selection pressures when it loses its value in a changing environment. The feature may be more urgently selected against when its function becomes definitely harmful, but if the lack of the feature provides no advantage, and its presence provides no disadvantage, the feature might not be eliminated by natural selection and persist among the species. Typical examples of both types occur in the loss of flight ability in species that inhabit oceans.
Introduction
Vestigial features can take various forms; for example, they may be behavior patterns, anatomical structures, or biochemical processes. Like most other physical features, however, vestigial functional features in a given species may successively appear, develop, and persist or disappear at various stages within the organism's life cycle, ranging from early embryonic development to adulthood. late.
Vestigiality, biologically speaking, refers to organisms that retain organs, which have apparently lost all of their original function. The issue is controversial and not without dispute; however, vestigial organs are common evolutionary knowledge. Additionally, the term vestigiality is useful to refer to many genetically determined characteristics, whether morphological, behavioral, or physiological; in any context, however, it need not follow that a vestigial feature must be completely useless. A classic example at the level of gross anatomy is the human vermiform appendix, although vestigial in the sense of not retaining significant digestive function, the appendix still has immunological functions and is useful in maintaining intestinal flora.
Similar concepts apply at the molecular level: some nucleic acid sequences in eukaryotic genomes have no known biological function; some of them may be 'junk DNA', but it is a difficult matter to prove that a particular sequence in a particular region of a given genome is really non-functional. Just because it's non-coding DNA doesn't mean it's functionless. Furthermore, even if an existing DNA sequence has no function, it does not follow that it descended from an ancestral functional DNA sequence. Logically, such DNA would not be vestigial in the sense of being the vestige of a functional structure. By contrast, pseudogenes have lost their protein-coding ability or are otherwise no longer expressed in the cell. Whether they have some existing function or not, they have lost their former function and in that sense they fit the definition of vestigiosity.
vestigial structures are often called vestigial organs, although many of them are not really organs. Such vestigial structures are typically degenerate, atrophied, or rudimentary, and tend to be much more variable than their counterpart non-vestigial parts. Although structures commonly considered "vestigial" they may have lost some or all of the functional roles they had played in ancestral organisms, such structures may retain minor functions, or may have adapted to new roles in existing populations.
It is important to avoid confusing the concept of vestigiality with that of exaptation. Both can appear together in the same example, depending on the relevant point of view. In short, a structure originally used for one purpose is modified for a new one. For example, penguin wings would be exact in the sense of serving a substantial new purpose (underwater locomotion), but could still be considered vestigial in the sense of having lost the flight function. In contrast, Darwin argued that the wings of emus would definitely be vestigial, since they appear to serve no important extant function; however, function is a matter of degree, so judgments about what is a "main" they are arbitrary; the emu appears to use its wings as balance organs when running. Similarly, the ostrich uses its wings for display and temperature control, although they are undoubtedly vestigial as structures for flight.
Vestigial characters range from detrimental to neutral to favorable in terms of selection. Some may be of some limited utility to an organism, but still degenerate over time if they do not confer a significant enough advantage in terms of fitness to avoid the effects of genetic drift or competitive selection pressures. Vestigiality in its various forms presents many examples of evidence for biological evolution.
History
Vestigial structures have been noted since ancient times and the reason for their existence was speculated long before Darwinian evolution provided a widely accepted explanation. In the 4th century BC, Aristotle was one of the first writers to comment, in his History of Animals, on the vestigial eyes of moles, calling them "developmental delay" due to the fact that moles can barely see. However, it was only in the last few centuries that anatomical remains became a subject of serious study. In 1798, Étienne Geoffroy Saint-Hilaire observed the vestigial structures:
While useless in this circumstance, these rudiments have not been eliminated, because nature never works for quick jumps, and always leaves traces of an organ, even though it is completely superfluous, if that organ plays an important role in the other species of the same family.
His colleague, Jean-Baptiste Lamarck, named a number of vestigial structures in his 1809 book Philosophie Zoologique. Lamarck noted that "Olivier's Spalax, which lives underground like the mole and is apparently exposed to daylight even less than the mole, has completely lost the use of sight: so that it shows nothing more than vestiges of this organ".
Charles Darwin was familiar with the concept of vestigial structures, although the term for them did not yet exist. He listed several of them in The Descent of Man, including the muscles of the ear, the wisdom teeth, the appendix, the tail bone, body hair, and the crescentic crease in the corner of the eye. Darwin also noted, in On the Origin of Species, that a vestigial structure might be useless for its primary function, but still retains secondary anatomical roles: "An organ that serves two purposes may become rudimentary or completely aborted by one, even more important purpose, and still perfectly efficient for the other... [A]n organ may be rendered rudimentary for its proper purpose and used for a different object".
In the first edition of The Origin of Species, Darwin briefly mentioned the inheritance of acquired characters under the heading "Effects of Use and Disuse", expressing little doubt that that use "strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited". In later editions he expanded his thoughts on this, and in the final chapter of the 6th edition he concluded that species have been modified "mainly through the natural selection of numerous successive, slight, favorable variations; helped significantly by the inherited effects of use and disuse of the parts".
In 1893, Robert Wiedersheim published The Structure of Man, a book on human anatomy and its relevance to the evolutionary history of man. The Structure of Man contained a list of 86 human organs that Wiedersheim described as "Organs that have become wholly or partly without function, some appearing only in the embryo, others present throughout life constantly or inconstantly." For the most part Organs which may justly be called Vestigial'. Since his time, the function of some of these structures has been discovered, while other anatomical remains have been unearthed, making the list of interest primarily as an overview. record of knowledge of human anatomy at that time. Later versions of the Wiedersheim list expanded to as many as 180 "vestigial organs" humans. This is why zoologist Horatio Newman said in a written statement in evidence at the Scopes trial that "According to Wiedersheim, there are no less than 180 vestigial structures in the human body, enough to make a man a true walking museum of antiquities."
Common ancestor and evolutionary theory
Vestigial structures are often homologous to normally functioning structures in other species. Therefore, the vestigial structures can be considered evidence of evolution, the process by which beneficial heritable traits emerge in populations over an extended period of time. The existence of rudimentary traits can be attributed to changes in the environment and behavior patterns of the organism in question. Through examination of these various traits, it is clear that evolution had a difficult role in the development of organisms. Every anatomical structure or behavioral response has origins in which, at some point, they were useful. As time passed, the ancient common ancestor organisms did as well. Evolving over time, natural selection played an important role. More advantageous structures were selected, while others were not. With this expansion, some features fell by the wayside. Since the trait function is no longer beneficial for survival, the probability that future offspring will inherit the "normal" of it decreases. In some cases, the structure becomes harmful to the organism (for example, a mole's eyes can become infected). In many cases, the structure does not cause direct damage, however, all structures require additional energy in terms of development, maintenance and weight, and are also a risk in terms of disease (eg infection, cancer), providing some pressure. selective for the removal of parts that do not contribute to the fitness of an organism. A structure that is not harmful will take longer to be 'removed' than it is. than one that is. However, some vestigial structures may persist due to developmental constraints such that complete loss of the structure could not occur without major alterations to the developmental pattern of the organism, and such alterations would likely produce numerous negative side effects. The toes of many animals, such as horses, which stand on a single toe, are still evident in a vestigial form and may become evident, albeit rarely, from time to time in individuals.
Vestigial versions of the structure can be compared to the original version of the structure in other species in order to determine the homology of a vestigial structure. Homologous structures indicate common ancestry with those organisms that have a functional version of the structure. Douglas J. Futuyma has stated that vestigial structures are meaningless without evolution, just as the spelling and usage of many modern English words can only be explained by their Latin or Old Norse antecedents.
Vestigial traits can still be considered adaptations. This is because an adaptation is often defined as a trait that has been favored by natural selection. Adaptations therefore need not be adaptive, as long as they were at some point.
Examples
Animals
Vestigial traits are present throughout the animal kingdom, and an almost endless list could be given. Darwin said that "it would be impossible to name one of the higher animals in which one part or another is not found in a rudimentary condition".
The wings of ostriches, emus, and other flightless birds are vestigial; they are remnants of the wings of their flying ancestors. The eyes of certain cave fish and salamanders are vestigial, since they do not allow the organism to see, and are remnants of the functional eyes of their ancestors. Animals that reproduce without sex (via asexual reproduction) generally lose their sexual characteristics, such as the ability to locate/recognize the opposite sex and copulatory behavior.
Boas and pythons have vestigial pelvises, which are visible externally as two small pelvic spicules on either side of the cloaca. These spurs are sometimes used in copulation, but they are not essential, as no colubroid snake (the vast majority of species) possesses these remains. Also, in most snakes, the left lung is greatly reduced or absent. Amphisbaenas, which independently developed limblessness, also retain vestiges of the pelvis and pectoral girdle, and have lost the right lung.
A case of vestigial organs in monogeneous polyopisthocotylean type (parasitic flatworms) was described. These parasites generally have a posterior attachment organ with several clamps, which are sclerotized organs that attach the worm to the gill of the host fish. These clamps are extremely important for the survival of the parasite. In the family Protomicrocotylidae, species have normal clamps, simplified clamps, or no clamps at all (in the genus Lethacotyle). After a comparative study of the relative area of clamps in more than 100 Monogeneans, this has been interpreted as an evolutionary sequence leading to loss of clamps. Coincidentally, other attachment structures (lateral flaps, transverse striae) have evolved in protomicrocots. Therefore, the clamps in Protomicrocotylidae were considered vestigial organs.
In the examples above, vestigiosity is usually the (sometimes incidental) result of adaptive evolution. However, there are many examples of vestigiality as the product of drastic mutation, and such vestigiousness is often deleterious or counteradaptive. One of the first documented examples was that of vestigial wings in Drosophila. Many examples in many other contexts have since emerged.
Humans
Human vestigiality is related to human evolution, and includes a variety of characters that occur in the human species. Many examples of these are vestigial in other primates and related animals, while other examples are still highly developed. The human cecum is vestigial, as is often the case in omnivores, and is reduced to a single chamber that receives the contents of the ileum in the colon. The ancestral caecum would have been a large caecum diverticulum in which tough plant material such as cellulose would have been fermented in preparation for absorption in the colon. Analogous organs in other human-like animals continue to perform similar functions. An alternative explanation would be the possibility that natural selection selected for larger appendages because smaller, thinner appendages would be more susceptible to inflammation and disease. The Coccyx, although a vestige of the tail of some ancestors of the primates, it is functional as an anchor for certain pelvic muscles, including: the levator ani muscle and the gluteus maximus muscle, the gluteus maximus muscle.
Other structures that are vestigial include the plica semilunaris in the inner corner of the eye (a remnant of the nictitating membrane); and, as depicted, the ear muscles and other parts of the body. Other organic structures (such as the occipitofrontalis muscle) have lost their original functions (preventing the head from falling) but are still useful for other purposes (facial expression).
Humans also have some vestigial behaviors and reflexes. The formation of goosebumps in humans under stress is a vestigial reflex; its function in human ancestors was to raise hair from the body, making the ancestor appear larger and warding off predators. The arrector pili muscularis, which is a band of smooth muscle that connects the hair follicle to the connective tissue, contracts and creates goosebumps.
There are also vestigial molecular structures in humans, which are no longer used, but which may indicate common ancestry with other species. An example of this is a gene that is functional in most other mammals and that produces L-gulonolactone oxidase, an enzyme that can produce vitamin C. A documented mutation disables the gene in one ancestor of the modern monkey and ape infraorder, and now remains in their genomes, including the human genome, as a vestigial sequence called a pseudogene.
The shift in the human diet toward soft and processed foods over time caused a reduction in the number of powerful grinding teeth, especially third molars, or wisdom teeth, which were highly prone to impaction.
Plants and fungi
Plants also have vestigial parts, including nonfunctional stipules and carpels, Equisetum leaf reduction, fungus paraphyses. Well-known examples are reductions in floral display, leading to smaller and/or pale flowers, in plants that reproduce without interbreeding, for example through selfing or obligate clonal reproduction.