Editing Evolution (section)

=== Common descent ===
{{Further|Common descent|Evidence of common descent}}

All organisms on Earth are descended from a common ancestor or ancestral [[gene pool]].<ref name="Penny-1999" /><ref>{{cite journal |last=Theobald |first=Douglas L. |date=13 May 2010 |title=A formal test of the theory of universal common ancestry |url=https://archive.org/details/sim_nature-uk_2010-05-13_465_7295/page/219 |journal=Nature |volume=465 |issue=7295 |pages=219–222 |bibcode=2010Natur.465..219T |doi=10.1038/nature09014 |issn=0028-0836 |pmid=20463738 |s2cid=4422345}}</ref> Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.<ref>{{cite journal |last1=Bapteste |first1=Eric |last2=Walsh |first2=David A. |date=June 2005 |title=Does the 'Ring of Life' ring true? |journal=[[Trends in Microbiology]] |volume=13 |issue=6 |pages=256–261 |doi=10.1016/j.tim.2005.03.012 |issn=0966-842X |pmid=15936656}}</ref> The common descent of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, [[vestigial trait]]s with no clear purpose resemble functional ancestral traits. Fourth, organisms can be classified using these similarities into a hierarchy of nested groups, similar to a family tree.<ref>{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=16 1]}}</ref>

[[File:Ape skeletons.png|upright=1.5|thumb|left|The [[hominoids]] are descendants of a [[common ancestor]].]]

Due to horizontal gene transfer, this "tree of life" may be more complicated than a simple branching tree, since some genes have spread independently between distantly related species.<ref>{{cite journal |last1=Doolittle |first1=W. Ford |last2=Bapteste |first2=Eric |date=13 February 2007 |title=Pattern pluralism and the Tree of Life hypothesis |journal=PNAS |volume=104 |issue=7 |pages=2043–2049 |bibcode=2007PNAS..104.2043D |doi=10.1073/pnas.0610699104 |issn=0027-8424 |pmc=1892968 |pmid=17261804 |doi-access=free}}</ref><ref>{{cite journal |last1=Kunin |first1=Victor |last2=Goldovsky |first2=Leon |last3=Darzentas |first3=Nikos |last4=Ouzounis |first4=Christos A. |date=July 2005 |title=The net of life: Reconstructing the microbial phylogenetic network |journal=Genome Research |volume=15 |issue=7 |pages=954–959 |doi=10.1101/gr.3666505 |issn=1088-9051 |pmid=15965028 |pmc=1172039}}</ref> To solve this problem and others, some authors prefer to use the "[[Coral of life]]" as a metaphor or a mathematical model to illustrate the evolution of life. This view dates back to an idea briefly mentioned by Darwin but later abandoned.<ref name="Bnotebook">{{harvnb|Darwin|1837|p=[http://darwin-online.org.uk/content/frameset?viewtype=side&itemID=CUL-DAR121.-&pageseq=27 25]}}</ref>

Past species have also left records of their evolutionary history. Fossils, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record.<ref name="Jablonski-1999">{{cite journal |last=Jablonski |first=David |s2cid=43388925 |date=25 June 1999 |title=The Future of the Fossil Record |journal=Science |volume=284 |issue=5423 |pages=2114–2116 |pmid=10381868 |doi=10.1126/science.284.5423.2114 |issn=0036-8075}}</ref> By comparing the anatomies of both modern and extinct species, palaeontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as bacteria and archaea share a limited set of common morphologies, their fossils do not provide information on their ancestry.

More recently, evidence for common descent has come from the study of biochemical similarities between organisms. For example, all living cells use the same basic set of nucleotides and [[amino acid]]s.<ref>{{cite journal |last=Mason |first=Stephen F. |date=6 September 1984 |title=Origins of biomolecular handedness |url=https://archive.org/details/sim_nature-uk_1984-09-06_311_5981/page/19 |journal=Nature |volume=311 |issue=5981 |pages=19–23 |bibcode=1984Natur.311...19M |doi=10.1038/311019a0 |issn=0028-0836 |pmid=6472461 |s2cid=103653}}</ref> The development of [[molecular genetics]] has revealed the record of evolution left in organisms' genomes: dating when species diverged through the [[molecular clock]] produced by mutations.<ref>{{cite journal |last1=Wolf |first1=Yuri I. |last2=Rogozin |first2=Igor B. |last3=Grishin |first3=Nick V. |last4=Koonin |first4=Eugene V. |author-link4=Eugene Koonin |date=1 September 2002 |title=Genome trees and the tree of life |url=https://archive.org/details/sim_trends-in-genetics_2002-09_18_9/page/472 |journal=Trends in Genetics |volume=18 |issue=9 |pages=472–479 |doi=10.1016/S0168-9525(02)02744-0 |issn=0168-9525 |pmid=12175808}}</ref> For example, these DNA sequence comparisons have revealed that humans and chimpanzees share 98% of their genomes and analysing the few areas where they differ helps shed light on when the common ancestor of these species existed.<ref>{{cite journal |last1=Varki |first1=Ajit |author-link1=Ajit Varki |last2=Altheide |first2=Tasha K. |date=December 2005 |title=Comparing the human and chimpanzee genomes: searching for needles in a haystack |journal=Genome Research |volume=15 |issue=12 |pages=1746–1758 |doi=10.1101/gr.3737405 |issn=1088-9051 |pmid=16339373 |citeseerx=10.1.1.673.9212}}</ref>