Common descent describes how, in evolutionary biology, a group of organisms share a most recent common ancestor. There is "massive" evidence of common descent of all life on Earth from the last universal common ancestor (LUCA). In July 2016, scientists reported identifying a set of 355 genes from the LUCA, by comparing the genomes of the three domains of life, archaea, bacteria, and eukaryotes.
Common ancestry between organisms of different species arises during speciation, in which new species are established from a single ancestral population. Organisms which share a more-recent common ancestor are more closely related. The most recent common ancestor of all currently living organisms is the last universal ancestor, which lived about 3.9 billion years ago. The two earliest evidences for life on Earth are graphite found to be biogenic in 3.7 billion-year-old metasedimentary rocks discovered in western Greenland and microbial mat fossils found in 3.48 billion-year-old sandstone discovered in Western Australia. All currently living organisms on Earth share a common genetic heritage, though the suggestion of substantial horizontal gene transfer during early evolution has led to questions about the monophyly (single ancestry) of life. 6,331 groups of genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian.
There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.
In the 1740s, the French mathematician Pierre Louis Maupertuis made the first known suggestion that all organisms had a common ancestor, and had diverged through random variation and natural selection. In Essai de cosmologie (1750), Maupertuis noted:
May we not say that, in the fortuitous combination of the productions of Nature, since only those creatures could survive in whose organizations a certain degree of adaptation was present, there is nothing extraordinary in the fact that such adaptation is actually found in all these species which now exist? Chance, one might say, turned out a vast number of individuals; a small proportion of these were organized in such a manner that the animals' organs could satisfy their needs. A much greater number showed neither adaptation nor order; these last have all perished.... Thus the species which we see today are but a small part of all those that a blind destiny has produced.
In 1794, Charles Darwin's grandfather, Erasmus Darwin asked:
[W]ould it be too bold to imagine, that in the great length of time, since the earth began to exist, perhaps millions of ages before the commencement of the history of mankind, would it be too bold to imagine, that all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality, with the power of acquiring new parts attended with new propensities, directed by irritations, sensations, volitions, and associations; and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down those improvements by generation to its posterity, world without end?
Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed.
But he precedes that remark by, "Analogy would lead me one step further, namely, to the belief that all animals and plants have descended from some one prototype. But analogy may be a deceitful guide." And in the subsequent edition , he asserts rather,
"We do not know all the possible transitional gradations between the simplest and the most perfect organs; it cannot be pretended that we know all the varied means of Distribution during the long lapse of years, or that we know how imperfect the Geological Record is. Grave as these several difficulties are, in my judgment they do not overthrow the theory of descent from a few created forms with subsequent modification".
Common descent was widely accepted amongst the scientific community after Darwin's publication. In 1907, Vernon Kellogg commented that "practically no naturalists of position and recognized attainment doubt the theory of descent."
In 2008, biologist T. Ryan Gregory noted that:
No reliable observation has ever been found to contradict the general notion of common descent. It should come as no surprise, then, that the scientific community at large has accepted evolutionary descent as a historical reality since Darwin’s time and considers it among the most reliably established and fundamentally important facts in all of science.
All known forms of life are based on the same fundamental biochemical organization: genetic information encoded in DNA, transcribed into RNA, through the effect of protein- and RNA-enzymes, then translated into proteins by (highly similar) ribosomes, with ATP, NADPH and others as energy sources. Analysis of small sequence differences in widely shared substances such as cytochrome c further supports universal common descent. Some 23 proteins are found in all organisms, serving as enzymes carrying out core functions like DNA replication. The fact that only one such set of enzymes exists is convincing evidence of a single ancestry. 6,331 genes common to all living animals have been identified; these may have arisen from a single common ancestor that lived 650 million years ago in the Precambrian.
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The genetic code (the "translation table" according to which DNA information is translated into amino acids, and hence proteins) is nearly identical for all known lifeforms, from bacteria and archaea to animals and plants. The universality of this code is generally regarded by biologists as definitive evidence in favor of universal common descent.
The way that codons (DNA triplets) are mapped to amino acids seems to be strongly optimised. Richard Egel argues that in particular the hydrophobic (non-polar) side-chains are well organised, suggesting that these enabled the earliest organisms to create peptides with water-repelling regions able to support the essential electron exchange (redox) reactions for energy transfer.
Similarities which have no adaptive relevance cannot be explained by convergent evolution, and therefore they provide compelling support for universal common descent. Such evidence has come from two areas: amino acid sequences and DNA sequences. Proteins with the same three-dimensional structure need not have identical amino acid sequences; any irrelevant similarity between the sequences is evidence for common descent. In certain cases, there are several codons (DNA triplets) that code redundantly for the same amino acid. Since many species use the same codon at the same place to specify an amino acid that can be represented by more than one codon, that is evidence for their sharing a recent common ancestor. Had the amino acid sequences come from different ancestors, they would have been coded for by any of the redundant codons, and since the correct amino acids would already have been in place, natural selection would not have driven any change in the codons, however much time was available. Genetic drift could change the codons, but it would be extremely unlikely to make all the redundant codons in a whole sequence match exactly across multiple lineages. Similarly, shared nucleotide sequences, especially where these are apparently neutral such as the positioning of introns and pseudogenes, provide strong evidence of common ancestry.
Biologists often point to the universality of many aspects of cellular life as supportive evidence to the more compelling evidence listed above. These similarities include the energy carrier adenosine triphosphate (ATP), and the fact that all amino acids found in proteins are left-handed. It is, however, possible that these similarities resulted because of the laws of physics and chemistry - rather than through universal common descent - and therefore resulted in convergent evolution. In contrast, there is evidence for homology of the central subunits of Transmembrane ATPases throughout all living organisms, especially how the rotating elements are bound to the membrane. This supports the assumption of a LUCA as a cellular organism, although primordial membranes may have been semipermeable and evolved later to the membranes of modern bacteria, and on a second path to those of modern archaea also.
Another important piece of evidence is from detailed phylogenetic trees (i.e., "genealogic trees" of species) mapping out the proposed divisions and common ancestors of all living species. In 2010, Douglas L. Theobald published a statistical analysis of available genetic data, mapping them to phylogenetic trees, that gave "strong quantitative support, by a formal test, for the unity of life."
Traditionally, these trees have been built using morphological methods, such as appearance, embryology, etc. Recently, it has been possible to construct these trees using molecular data, based on similarities and differences between genetic and protein sequences. All these methods produce essentially similar results, even though most genetic variation has no influence over external morphology. That phylogenetic trees based on different types of information agree with each other is strong evidence of a real underlying common descent.
Theobald noted that substantial horizontal gene transfer could have occurred during early evolution. Bacteria today remain capable of gene exchange between distantly-related lineages. This weakens the basic assumption of phylogenetic analysis, that similarity of genomes implies common ancestry, because sufficient gene exchange would allow lineages to share much of their genome whether or not they shared an ancestor (monophyly). This has led to questions about the single ancestry of life. However, biologists consider it very unlikely that completely unrelated proto-organisms could have exchanged genes, as their different coding mechanisms would have resulted only in garble rather than functioning systems. Later, however, many organisms all derived from a single ancestor could readily have shared genes that all worked in the same way, and it appears that they have.
If early organisms had been driven by the same environmental conditions to evolve similar biochemistry convergently, they might independently have acquired similar genetic sequences. Theobald's "formal test" was accordingly criticised by Takahiro Yonezawa and colleagues for not including consideration of convergence. They argued that Theobald's test was insufficient to distinguish between the competing hypotheses. Theobald has defended his method against this claim, arguing that his tests distinguish between phylogenetic structure and mere sequence similarity. Therefore, Theobald argued, his results show that "real universally conserved proteins are homologous."
Amphiesmenoptera is an insect superorder, established by S. G. Kiriakoff, but often credited to Willi Hennig in his revision of insect taxonomy for two sister orders: Lepidoptera (butterflies and moths) and Trichoptera (caddisflies). In 2017, a third fossil order was added to the group, the Tarachoptera.Trichoptera and Lepidoptera share a number of derived characters (synapomorphies) which demonstrate their common descent:
Females, rather than males, are heterogametic (i.e. their sex chromosomes differ).
Dense setae are present in the wings (modified into scales in Lepidoptera).
There is a particular venation pattern on the forewings (the double-looped anal veins).
Larvae have mouth structures and glands to make and manipulate silk.Thus these two extant orders are sisters, with Tarachoptera basal to both groups. Amphiesmenoptera probably evolved in the Jurassic. Lepidoptera differ from the Trichoptera in several features, including wing venation, form of the scales on the wings, loss of the cerci, loss of an ocellus, and changes to the legs.Amphiesmenoptera are thought to be the sister group of Antliophora, a proposed superorder comprising Diptera (flies), Siphonaptera (fleas) and Mecoptera (scorpionflies). Together, Amphiesmenoptera and Antliophora compose the group Mecopterida.Ancestor
An ancestor is a parent or (recursively) the parent of an antecedent (i.e., a grandparent, great-grandparent, great-great-grandparent, and so forth). Ancestor is "any person from whom one is descended. In law the person from whom an estate has been inherited."Two individuals have a genetic relationship if one is the ancestor of the other, or if they share a common ancestor. In evolutionary theory, species which share an evolutionary ancestor are said to be of common descent. However, this concept of ancestry does not apply to some bacteria and other organisms capable of horizontal gene transfer. Some research suggests that the average person has twice as many female ancestors as male ancestors. This might have been due to the past prevalence of polygynous relations and female hypergamy.Assuming that all of an individual's ancestors are otherwise unrelated to each other, that individual has 2n ancestors in the nth generation before him and a total of 2g+1 − 2 ancestors in the g generations before him. In practice, however, it is clear that most ancestors of humans (and any other species) are multiply related (see pedigree collapse). Consider n = 40: the human species is mors, both living and dead; in contrast, some more youth-oriented cultural contexts display less veneration of elders. In other cultural contexts, some people seek providence from their deceased ancestors; this practice is sometimes known as ancestor worship or, more accurately, ancestor veneration.Comparative anatomy
Comparative anatomy is the study of similarities and differences in the anatomy of different species. It is closely related to evolutionary biology and phylogeny (the evolution of species).
The science began in the classical era, continuing in Early Modern times with work by Pierre Belon who noted the similarities of the skeletons of birds and humans.
Comparative anatomy has provided evidence of common descent, and has assisted in the classification of animals.Created kind
In Christian and Jewish creationism, a religious view based on the creation account of the book of Genesis, created kinds are purported to be the original forms of life as they were created by God. They are also referred to as kinds, original kinds, Genesis kinds, and baramin (a neologism coined by combining the Hebrew words bara [created] and min [kind], though the combination does not work syntactically in actual Hebrew). The idea is promulgated by young Earth creationist organizations and preachers as a means to support their belief in the literal veracity of the Genesis creation myth as well as their contention that the ancestors of all land-based life on Earth were housed on Noah's ark before a great flood. Old earth creationists also employ the concept, rejecting the idea of common descent. In contrast to young Earth creationists, old earth creationists do not necessarily believe all land-based life was housed on the ark, and some accept some evolutionary change within the given kinds has occurred.
In contrast to the scientific theory of common descent, these creationists argue that not all life on Earth is related, but that life was created by God in a finite number of discrete forms. This viewpoint claims that kinds cannot interbreed and have no evolutionary relationship to one another.Devlin (surname)
O'Devlin (Irish: Ó Doibhilin) is the surname of a Gaelic Irish family of the Uí Néill who were chiefs in the far northeastern of the present-day County of Tyrone, bordering on Lough Neagh and the Ballinderry River. The O'Develins claimed a common descent from Develin (in Irish: Dobhuilen or "Raging Valour", an Irish noble of the royal blood of Aileach who flourished in or about the eighth century AD and was eighth in descent from Owen, the founder of the clan). Develin was a scion of that branch of the clan Owen known as the Sons of Erca (Cenel Mic Erca) because of their descent from Muirchertach Mac Erca, grandson of Owen.Evidence of common descent
Evidence of common descent of living organisms has been discovered by scientists researching in a variety of disciplines over many decades, demonstrating that all life on Earth comes from a single ancestor. This forms an important part of the evidence on which evolutionary theory rests, demonstrates that evolution does occur, and illustrates the processes that created Earth's biodiversity. It supports the modern evolutionary synthesis—the current scientific theory that explains how and why life changes over time. Evolutionary biologists document evidence of common descent, all the way back to the last universal common ancestor, by developing testable predictions, testing hypotheses, and constructing theories that illustrate and describe its causes.
Comparison of the DNA genetic sequences of organisms has revealed that organisms that are phylogenetically close have a higher degree of DNA sequence similarity than organisms that are phylogenetically distant. Genetic fragments such as pseudogenes, regions of DNA that are orthologous to a gene in a related organism, but are no longer active and appear to be undergoing a steady process of degeneration from cumulative mutations support common descent alongside the universal biochemical organization and molecular variance patterns found in all organisms. Additional genetic information conclusively supports the relatedness of life and has allowed scientists (since the discovery of DNA) to develop phylogenetic trees: a construction of organisms evolutionary relatedness. It has also led to the development of molecular clock techniques to date taxon divergence times and to calibrate these with the fossil record.
Fossils are important for estimating when various lineages developed in geologic time. As fossilization is an uncommon occurrence, usually requiring hard body parts and death near a site where sediments are being deposited, the fossil record only provides sparse and intermittent information about the evolution of life. Evidence of organisms prior to the development of hard body parts such as shells, bones and teeth is especially scarce, but exists in the form of ancient microfossils, as well as impressions of various soft-bodied organisms. The comparative study of the anatomy of groups of animals shows structural features that are fundamentally similar (homologous), demonstrating phylogenetic and ancestral relationships with other organisms, most especially when compared with fossils of ancient extinct organisms. Vestigial structures and comparisons in embryonic development are largely a contributing factor in anatomical resemblance in concordance with common descent. Since metabolic processes do not leave fossils, research into the evolution of the basic cellular processes is done largely by comparison of existing organisms' physiology and biochemistry. Many lineages diverged at different stages of development, so it is possible to determine when certain metabolic processes appeared by comparing the traits of the descendants of a common ancestor.
Evidence from animal coloration was gathered by some of Darwin's contemporaries; camouflage, mimicry, and warning coloration are all readily explained by natural selection. Special cases like the seasonal changes in the plumage of the ptarmigan, camouflaging it against snow in winter and against brown moorland in summer provide compelling evidence that selection is at work. Further evidence comes from the field of biogeography because evolution with common descent provides the best and most thorough explanation for a variety of facts concerning the geographical distribution of plants and animals across the world. This is especially obvious in the field of insular biogeography. Combined with the well-established geological theory of plate tectonics, common descent provides a way to combine facts about the current distribution of species with evidence from the fossil record to provide a logically consistent explanation of how the distribution of living organisms has changed over time.
The development and spread of antibiotic resistant bacteria provides evidence that evolution due to natural selection is an ongoing process in the natural world. Natural selection is ubiquitous in all research pertaining to evolution, taking note of the fact that all of the following examples in each section of the article document the process. Alongside this are observed instances of the separation of populations of species into sets of new species (speciation). Speciation has been observed in the lab and in nature. Multiple forms of such have been described and documented as examples for individual modes of speciation. Furthermore, evidence of common descent extends from direct laboratory experimentation with the selective breeding of organisms—historically and currently—and other controlled experiments involving many of the topics in the article. This article summarizes the varying disciplines that provide the evidence for evolution and the common descent of all life on Earth, accompanied by numerous and specialized examples, indicating a compelling consilience of evidence.Evolution as fact and theory
Many scientists and philosophers of science have described evolution as fact and theory, a phrase which was used as the title of an article by paleontologist Stephen Jay Gould in 1981. He describes fact in science as meaning data, not absolute certainty but "confirmed to such a degree that it would be perverse to withhold provisional assent". A scientific theory is a well-substantiated explanation of such facts. The facts of evolution come from observational evidence of current processes, from imperfections in organisms recording historical common descent, and from transitions in the fossil record. Theories of evolution provide a provisional explanation for these facts.Each of the words "evolution", "fact" and "theory" has several meanings in different contexts. Evolution means change over time, as in stellar evolution. In biology it refers to observed changes in organisms, to their descent from a common ancestor, and at a technical level to a change in gene frequency over time; it can also refer to explanatory theories (such as Charles Darwin's theory of natural selection) which explain the mechanisms of evolution. To a scientist, fact can describe a repeatable observation that all can agree on; it can refer to something that is so well established that nobody in a community disagrees with it; and it can also refer to the truth or falsity of a proposition. To the public, theory can mean an opinion or conjecture (e.g., "it's only a theory"), but among scientists it has a much stronger connotation of "well-substantiated explanation". With this number of choices, people can often talk past each other, and meanings become the subject of linguistic analysis.
Evidence for evolution continues to be accumulated and tested. The scientific literature includes statements by evolutionary biologists and philosophers of science demonstrating some of the different perspectives on evolution as fact and theory.Evolutionary biology
Evolutionary biology is the subfield of biology that studies the evolutionary processes that produced the diversity of life on Earth, starting from a single common ancestor. These processes include natural selection, common descent, and speciation.
The discipline emerged through what Julian Huxley called the modern synthesis (of the 1930s) of understanding from several previously unrelated fields of biological research, including genetics, ecology, systematics, and paleontology.
Current research has widened to cover the genetic architecture of adaptation, molecular evolution, and the different forces that contribute to evolution including sexual selection, genetic drift and biogeography. The newer field of evolutionary developmental biology ("evo-devo") investigates how embryonic development is controlled, thus creating a wider synthesis that integrates developmental biology with the fields covered by the earlier evolutionary synthesis.Evolutionary ecology
Evolutionary ecology lies at the intersection of ecology and evolutionary biology. It approaches the study of ecology in a way that explicitly considers the evolutionary histories of species and the interactions between them. Conversely, it can be seen as an approach to the study of evolution that incorporates an understanding of the interactions between the species under consideration. The main subfields of evolutionary ecology are life history evolution, sociobiology (the evolution of social behavior), the evolution of inter specific relations (cooperation, predator–prey interactions, parasitism, mutualism) and the evolution of biodiversity and of communities.
Evolutionary ecology mostly considers two things: how interactions (both among species and between species and their physical environment) shape species through selection and adaptation, and the consequences of the resulting evolutionary change.Genetic variation
Genetic variation describes the difference in DNA among individuals. There are multiple sources of genetic variation, including Mutation and Genetic recombination.Index of evolutionary biology articles
This is a list of topics in evolutionary biology.Is Genesis History?
Is Genesis History? is a 2017 American Christian film that uses creation science, a pseudoscientific concept, to promote Young Earth creationist beliefs that contradict established scientific facts regarding the origin of the Universe, the age of the Earth, and the common descent of all lifeforms.The film was written, directed, and produced by Thomas Purifoy Jr., who said he was inspired to make it after his daughter watched the Bill Nye–Ken Ham debate in 2014 and began asking him questions about the creation–evolution controversy. Del Tackett, the creator of Focus on the Family's "The Truth Project", narrates the film. Interviewing thirteen creationists, the narrator of the film argues that Genesis portrays real historical events. Other speakers include George Grant, Paul Nelson, Marcus R. Ross, Andrew A. Snelling, and Kurt Wise, as well as Larry Vardiman in the film's bonus features.
Is Genesis History? was released into American theaters on Thursday, February 23, 2017. It was shown in 704 theaters and grossed $1.8 million in one night. Over 143,000 people saw the film that night, and its box office earnings were the highest of any film in theaters in the United States that night. The film was shown again in theaters on March 2 and 7, 2017 in the United States, as well as in Canada on March 14, 2017. The film went on to earn a total box office of $2.6 million, after the encore showings. The film was re-released in around 850 theaters for an anniversary showing on February 22, 2018, with a bonus scene of Wheaton College students touring the Ark Encounter, a creationist attraction operated by Answers in Genesis. The students were members of a creationist club which had requested a screening of the film, leading to controversy among the Christian school's faculty, nearly all of whom reject the "historical creationism" that Is Genesis History? presents.Last universal common ancestor
The last universal common ancestor (LUCA), also called the last universal ancestor (LUA), cenancestor, or (incorrectly) progenote, is the most recent population of organisms from which all organisms now living on Earth have a common descent. LUCA is the most recent common ancestor of all current life on Earth. LUCA is not thought to be the first living organism on Earth, but only one of many early organisms, whereas the others became extinct.
While there is no specific fossil evidence of LUCA, it can be studied by comparing the genomes of its descendants, all organisms known to be living today. By this means, a 2016 study identified a set of 355 genes inferred to have been present in LUCA. This would imply it was already a complex life form with many co-adapted features, including transcription and translation mechanisms to convert information between DNA, RNA, and proteins. However, some of those genes could have developed later and spread universally by horizontal gene transfer between archaea and bacteria.LUCA is estimated to have lived some 3.5 to 3.8 billion years ago in the Paleoarchean era, a few hundred million years after the earliest evidence of life on Earth, for which there are several candidates. Microbial mat fossils have been found in 3.48 billion-year-old sandstone from Western Australia, while biogenic graphite has been found in 3.7 billion-year-old metamorphized sedimentary rocks from Western Greenland. Recent studies have tentatively proposed evidence of life as early as 4.28 billion years ago.Charles Darwin proposed the theory of universal common descent through an evolutionary process in his book On the Origin of Species in 1859, saying, "Therefore I should infer from analogy that probably all the organic beings which have ever lived on this earth have descended from some one primordial form, into which life was first breathed." Later biologists have separated the problem of the origin of life from that of the LUCA.Macroevolution
Macroevolution is evolution on a scale at or above the level of species, in contrast with microevolution, which refers to smaller evolutionary changes of allele frequencies within a species or population. Macroevolution and microevolution describe fundamentally identical processes on different time scales.The process of speciation may fall within the purview of either, depending on the forces thought to drive it. Paleontology, evolutionary developmental biology, comparative genomics and genomic phylostratigraphy contribute most of the evidence for macroevolution's patterns and processes.Mating type
Mating types are molecular mechanisms that regulate compatibility in sexually reproducing eukaryotes. They occur in isogamous and anisogamous species. Depending on the group, different mating types are often referred to by numbers, letters, or simply "+" and "-" instead of "male" and "female", that refer to "sexes" or differences in size between gametes. Syngamy can only take place between gametes carrying different mating types.
Reproduction regulated by mating types is especially prevalent in fungi. Filamentous ascomycetes usually have two mating types referred to as "MAT1-1" and "MAT1-2", following the yeast mating type locus MAT. Under standard nomenclature, MAT1-1 (which may informally be called MAT1) encodes for a regulatory protein with a high motility-group (HMG) DNA-binding motif, while MAT1-2 (informally called MAT2) encodes for a protein with an alpha box motif, as in the yeast mating type MATα1. The corresponding mating types in yeast, a non-filamentous ascomycete, are referred to as MATa and MATα.
Mating type genes in ascomycetes are called idiomorphs rather than alleles due to the uncertainty of the origin by common descent. The proteins they encode are transcription factors that regulate both the early and late stages of the sexual cycle. Heterothallic ascomycetes produce gametes that present a single Mat idiomorph and syngamy will only be possible between gametes carrying complementary mating types. On the other hand, homothallic ascomycetes produce gametes that can fuse with every other gamete in the population (including its own mitotic descendants) most often because each haploid contains the two alternate forms of the Mat locus in its genome.Basidiomycetes on the other hand can have thousands of different mating types.The adaptive function of mating type in the ascomycete Neurospora crassa is discussed in the article Neurospora crassa. That matings in N. crassa are restricted to interaction of strains of opposite mating type may be an adaptation to promote some degree of outcrossing. Outcrossing, through complementation, could provide the benefit of masking recessive deleterious mutations in genes that function in the dikaryon and/or diploid stage of the life cycle.Monogenism
Monogenism or sometimes monogenesis is the theory of human origins which posits a common descent for all human races. The negation of monogenism is polygenism. This issue was hotly debated in the Western world in the nineteenth century, as the assumptions of scientific racism came under scrutiny both from religious groups and in the light of developments in the life sciences and human science. It was integral to early conceptions of ethnology.
Modern scientific views favor this theory, with the most widely accepted model for human origins being the "Out of Africa" theory.Norse clans
The Scandinavian clan or ætt/ätt (pronounced [ˈæːtː] in Old Norse) was a social group based on common descent.Unilineality
Unilineality is a system of determining descent groups in which one belongs to one's father's or mother's line, whereby one's descent is traced either exclusively through male ancestors (patriline), or exclusively through female ancestors (matriline). Both patrilineality and matrilineality are types of unilineal descent. The main types of the unilineal descent groups are lineages and clans.
A lineage is a unilineal descent group that can demonstrate their common descent from a known apical ancestor.Vestigiality
Vestigiality is the retention during the process of evolution of genetically determined structures or attributes that have lost some or all of their ancestral function in a given species. Assessment of the vestigiality must generally rely on comparison with homologous features in related species. The emergence of vestigiality occurs by normal evolutionary processes, typically by loss of function of a feature that is no longer subject to positive selection pressures when it loses its value in a changing environment. The feature may be selected against more urgently when its function becomes definitively harmful, but if the lack of the feature provides no advantage, and its presence provides no disadvantage, the feature may not be phased out by natural selection and persist across species.
Examples of vestigial structures are the loss of functional wings in island-dwelling birds; the human appendix and vomeronasal organ; and the hindlimbs of the snake and whale.
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