Editing Evolution (section)

== Evolutionary history of life ==

{{align|right|{{Life timeline}} }}
{{Main|Evolutionary history of life}}
{{See also|Timeline of the evolutionary history of life}}

=== Origin of life ===
{{Further|Abiogenesis|Earliest known life forms|Panspermia|RNA world hypothesis}}

The Earth is [[Age of Earth|about 4.54&nbsp;billion years old]].<ref name="USGS-2007">{{cite web |url=http://pubs.usgs.gov/gip/geotime/age.html |title=Age of the Earth |date=9 July 2007 |publisher=[[United States Geological Survey]] |access-date=31 May 2015 |url-status=live |archive-url=https://web.archive.org/web/20051223072700/http://pubs.usgs.gov/gip/geotime/age.html |archive-date=23 December 2005}}</ref><ref name="Dalrymple-2001">{{harvnb|Dalrymple|2001|pp=205–221}}</ref><ref name="Manhesa-1980">{{cite journal |last1=Manhesa |first1=Gérard |last2=Allègre |first2=Claude J. |author-link2=Claude Allègre |last3=Dupréa |first3=Bernard |last4=Hamelin |first4=Bruno |date=May 1980 |title=Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics |url=https://archive.org/details/sim_earth-and-planetary-science-letters_1980-05_47_3/page/370 |journal=[[Earth and Planetary Science Letters]] |volume=47 |issue=3 |pages=370–382 |bibcode=1980E&PSL..47..370M |doi=10.1016/0012-821X(80)90024-2 |issn=0012-821X}}</ref> The earliest undisputed evidence of life on Earth dates from at least 3.5&nbsp;billion years ago,<ref name="Schopf-2007">{{cite journal |last1=Schopf |first1=J. William |author-link1=J. William Schopf |last2=Kudryavtsev |first2=Anatoliy B. |last3=Czaja |first3=Andrew D. |last4=Tripathi |first4=Abhishek B. |date=5 October 2007 |title=Evidence of Archean life: Stromatolites and microfossils |journal=[[Precambrian Research]] |volume=158 |pages=141–155 |issue=3–4 |doi=10.1016/j.precamres.2007.04.009 |issn=0301-9268 |bibcode=2007PreR..158..141S}}</ref><ref name="RavenJohnson2002">{{harvnb|Raven|Johnson|2002|p=68}}</ref> during the [[Eoarchean]] Era after a geological [[Crust (geology)|crust]] started to solidify following the earlier molten [[Hadean]] Eon. Microbial mat fossils have been found in 3.48&nbsp;billion-year-old sandstone in Western Australia.<ref name="Borenstein-2013">{{cite news |last=Borenstein |first=Seth |date=13 November 2013 |title=Oldest fossil found: Meet your microbial mom |url=http://apnews.excite.com/article/20131113/DAA1VSC01.html |work=[[Excite (web portal)|Excite]] |location=Yonkers, New York |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |access-date=31 May 2015 |url-status=live |archive-url=https://web.archive.org/web/20150629230719/http://apnews.excite.com/article/20131113/DAA1VSC01.html |archive-date=29 June 2015}}</ref><ref name="Pearlman-2013">{{cite news |last=Pearlman |first=Jonathan |date=13 November 2013 |title=Oldest signs of life on Earth found |url=https://www.telegraph.co.uk/news/science/science-news/10445788/Oldest-signs-of-life-on-Earth-found.html |newspaper=[[The Daily Telegraph]] |location=London |access-date=15 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20141216062531/http://www.telegraph.co.uk/news/science/science-news/10445788/Oldest-signs-of-life-on-Earth-found.html |archive-date=16 December 2014}}</ref><ref name="Noffke-2013">{{cite journal |last1=Noffke |first1=Nora |author1-link=Nora Noffke |last2=Christian |first2=Daniel |last3=Wacey |first3=David |last4=Hazen |first4=Robert M. |author-link4=Robert Hazen |date=16 November 2013 |title=Microbially Induced Sedimentary Structures Recording an Ancient Ecosystem in the ''ca.'' 3.48 Billion-Year-Old Dresser Formation, Pilbara, Western Australia |journal=[[Astrobiology (journal)|Astrobiology]] |volume=13 |issue=12 |pages=1103–1124 |bibcode=2013AsBio..13.1103N |doi=10.1089/ast.2013.1030 |issn=1531-1074 |pmc=3870916 |pmid=24205812}}</ref> Other early physical evidence of a biogenic substance is graphite in 3.7&nbsp;billion-year-old [[metasediment]]ary rocks discovered in Western Greenland<ref name="Ohtomo-2014">{{cite journal |last1=Ohtomo |first1=Yoko |last2=Kakegawa |first2=Takeshi |last3=Ishida |first3=Akizumi |last4=Nagase |first4=Toshiro |last5=Rosing |first5=Minik T. |display-authors=3 |date=January 2014 |title=Evidence for biogenic graphite in early Archaean Isua metasedimentary rocks |journal=[[Nature Geoscience]] |volume=7 |issue=1 |pages=25–28 |bibcode=2014NatGe...7...25O |doi=10.1038/ngeo2025 |issn=1752-0894}}</ref> as well as "remains of [[biotic life]]" found in 4.1&nbsp;billion-year-old rocks in Western Australia.<ref name="Borenstein-2015">{{cite news |last=Borenstein |first=Seth |title=Hints of life on what was thought to be desolate early Earth |url=http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |date=19 October 2015 |work=[[Excite (web portal)|Excite]] |location=Yonkers, NY |publisher=[[Mindspark Interactive Network]] |agency=[[Associated Press]] |archive-url=https://web.archive.org/web/20151023200248/http://apnews.excite.com/article/20151019/us-sci--earliest_life-a400435d0d.html |archive-date=23 October 2015 |access-date=8 October 2018}}</ref><ref name="Bell-2015">{{cite journal |last1=Bell |first1=Elizabeth A. |last2=Boehnike |first2=Patrick |last3=Harrison |first3=T. Mark |last4=Mao |first4=Wendy L. |author4-link=Wendy Mao |date=24 November 2015 |title=Potentially biogenic carbon preserved in a 4.1 billion-year-old zircon |url=http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf |journal=PNAS |volume=112 |issue=47 |pages=14518–14521 |doi=10.1073/pnas.1517557112 |issn=0027-8424 |access-date=30 December 2015 |pmid=26483481 |pmc=4664351 |bibcode=2015PNAS..11214518B |url-status=live |archive-url=https://web.archive.org/web/20151106021508/http://www.pnas.org/content/early/2015/10/14/1517557112.full.pdf |archive-date=6 November 2015 |doi-access=free}}</ref> Commenting on the Australian findings, [[Stephen Blair Hedges]] wrote: "If life arose relatively quickly on Earth, then it could be common in the universe."<ref name="Borenstein-2015" /><ref>{{cite news |last=Schouten |first=Lucy |date=20 October 2015 |title=When did life first emerge on Earth? Maybe a lot earlier than we thought |url=https://www.csmonitor.com/Science/2015/1020/When-did-life-first-emerge-on-Earth-Maybe-a-lot-earlier-than-we-thought |work=[[The Christian Science Monitor]] |location=Boston, Massachusetts |publisher=[[Christian Science Publishing Society]] |issn=0882-7729 |archive-url=https://web.archive.org/web/20160322214217/http://www.csmonitor.com/Science/2015/1020/When-did-life-first-emerge-on-Earth-Maybe-a-lot-earlier-than-we-thought |archive-date=22 March 2016 |url-status=live |access-date=11 July 2018}}</ref> <!---Nevertheless, [[Late Heavy Bombardment#Geological consequences on Earth|several studies]] suggest that life on Earth may have started even earlier,<ref name="AB-20021014">{{cite web |last=Tenenbaum |first=David |title=When Did Life on Earth Begin? Ask a Rock |url=http://www.astrobio.net/exclusive/293/when-did-life-on-earth-begin-ask-a-rock |date=14 October 2002 |work=Astrobiology Magazine |access-date=13 April 2014 |archive-url=https://web.archive.org/web/20210628022131/https://www.astrobio.net/news-exclusive/when-did-life-on-earth-begin-ask-a-rock/ |archive-date=28 June 2021 |url-status=usurped}}</ref> as early as 4.25 billion years ago according to one study,<ref name="NS-20080702">{{cite web |last=Courtland |first=Rachel |title=Did newborn Earth harbour life? |url=https://www.newscientist.com/article/dn14245-did-newborn-earth-harbour-life.html |date=2 July 2008 |work=[[New Scientist]] |access-date=13 April 2014}}</ref> and 4.4 billion years ago according to another study.<ref name="RN-20090520">{{cite web |last=Steenhuysen |first=Julie |title=Study turns back clock on origins of life on Earth |url=https://www.reuters.com/article/2009/05/20/us-asteroids-idUSTRE54J5PX20090520 |date=20 May 2009 |work=[[Reuters]] |access-date=13 April 2014}}</ref>---> In July 2016, scientists reported identifying a set of 355 [[gene]]s from the [[last universal common ancestor]] (LUCA) of all organisms living on Earth.<ref name="Wade-2016">{{cite news |last=Wade |first=Nicholas |author-link=Nicholas Wade |title=Meet Luca, the Ancestor of All Living Things |url=https://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html |date=25 July 2016 |newspaper=[[The New York Times]] |location=New York |issn=0362-4331 |access-date=25 July 2016 |url-status=live |archive-url=https://web.archive.org/web/20160728053822/http://www.nytimes.com/2016/07/26/science/last-universal-ancestor.html |archive-date=28 July 2016}}</ref>

More than 99% of all species, amounting to over five billion species,<ref name="Book-Biology">{{harvnb|McKinney|1997|p=[https://books.google.com/books?id=4LHnCAAAQBAJ&pg=PA110 110]}}</ref> that ever lived on Earth are estimated to be extinct.<ref name="Stearns-1999" /><ref name="Novacek-2014">{{cite news |last=Novacek |first=Michael J. |date=8 November 2014 |title=Prehistory's Brilliant Future |url=https://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |newspaper=The New York Times |location=New York |issn=0362-4331 |access-date=25 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20141229225657/http://www.nytimes.com/2014/11/09/opinion/sunday/prehistorys-brilliant-future.html |archive-date=29 December 2014}}</ref> Estimates on the number of Earth's current species range from 10&nbsp;million to 14&nbsp;million,<ref name="Mora-2011">{{cite journal |last1=Mora |first1=Camilo |last2=Tittensor |first2=Derek P. |last3=Adl |first3=Sina |last4=Simpson |first4=Alastair G. B. |last5=Worm |first5=Boris |author-link5=Boris Worm |display-authors=3 |date=23 August 2011 |title=How Many Species Are There on Earth and in the Ocean? |journal=PLOS Biology |volume=9 |issue=8 |page=e1001127 |doi=10.1371/journal.pbio.1001127 |issn=1545-7885 |pmc=3160336 |pmid=21886479 |doi-access=free}}</ref><ref name="Miller">{{harvnb|Miller|Spoolman|2012|p=[https://books.google.com/books?id=NYEJAAAAQBAJ&pg=PA62 62]}}</ref> of which about 1.9&nbsp;million are estimated to have been named<ref name="Chapman2009">{{harvnb|Chapman|2009}}</ref> and 1.6&nbsp;million documented in a central database to date,<ref name="Roskov-2016">{{cite web |url=http://www.catalogueoflife.org/annual-checklist/2016/info/ac |title=Species 2000 & ITIS Catalogue of Life, 2016 Annual Checklist |year=2016 |editor-last=Roskov |editor-first=Y. |editor2-last=Abucay |editor2-first=L. |editor3-last=Orrell |editor3-first=T. |editor4-last=Nicolson |editor4-first=D. |editor5-last=Flann |editor5-first=C. |editor6-last=Bailly |editor6-first=N. |editor7-last=Kirk |editor7-first=P. |editor8-last=Bourgoin |editor8-first=T. |editor9-last=DeWalt |editor9-first=R. E. |editor10-last=Decock |editor10-first=W. |editor11-last=De Wever |editor11-first=A. |display-editors=4 |website=Species 2000 |publisher=[[Naturalis Biodiversity Center]] |location=Leiden, Netherlands |issn=2405-884X |access-date=6 November 2016 |url-status=live |archive-url=https://web.archive.org/web/20161112121623/http://www.catalogueoflife.org/annual-checklist/2016/info/ac |archive-date=12 November 2016}}</ref> leaving at least 80% not yet described.

Highly energetic chemistry is thought to have produced a self-replicating molecule around 4&nbsp;billion years ago, and half a billion years later the last common ancestor of all life existed.<ref name="Doolittle-2000" /> The current scientific consensus is that the complex biochemistry that makes up life came from simpler chemical reactions.<ref>{{cite journal |last=Peretó |first=Juli |date=March 2005 |title=Controversies on the origin of life |url=http://www.im.microbios.org/0801/0801023.pdf |journal=International Microbiology |volume=8 |issue=1 |pages=23–31 |issn=1139-6709 |pmid=15906258 |archive-url=https://web.archive.org/web/20150824074726/http://www.im.microbios.org/0801/0801023.pdf |archive-date=24 August 2015}}</ref><ref name="BBC-20201111">{{cite news |last=Marshall |first=Michael |title=Charles Darwin's hunch about early life was probably right – In a few scrawled notes to a friend, biologist Charles Darwin theorised how life began. Not only was it probably correct, his theory was a century ahead of its time. |url=https://www.bbc.com/future/article/20201110-charles-darwin-early-life-theory |date=11 November 2020 |work=[[BBC News]] |access-date=11 November 2020 |archive-date=11 November 2020 |archive-url=https://web.archive.org/web/20201111015900/https://www.bbc.com/future/article/20201110-charles-darwin-early-life-theory |url-status=live}}</ref> The beginning of life may have included self-replicating molecules such as [[RNA]]<ref>{{cite journal |last=Joyce |first=Gerald F. |author-link=Gerald Joyce |date=11 July 2002 |title=The antiquity of RNA-based evolution |journal=Nature |volume=418 |issue=6894 |pages=214–221 |bibcode=2002Natur.418..214J |doi=10.1038/418214a |pmid=12110897 |s2cid=4331004}}</ref> and the assembly of simple cells.<ref>{{cite journal |last1=Trevors |first1=Jack T. |last2=Psenner |first2=Roland |date=December 2001 |title=From self-assembly of life to present-day bacteria: a possible role for nanocells |journal=FEMS Microbiology Reviews |volume=25 |issue=5 |pages=573–582 |doi=10.1111/j.1574-6976.2001.tb00592.x |issn=1574-6976 |pmid=11742692 |doi-access=free}}</ref>

=== 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>

=== Evolution of life ===
{{Main|Evolutionary history of life|Timeline of evolutionary history of life}}

{{PhylomapA|size=320px|align=right|caption=[[Evolutionary tree]] showing the divergence of modern species from their common ancestor in the centre.<ref name="Ciccarelli-2006">{{cite journal |last1=Ciccarelli |first1=Francesca D. |last2=Doerks |first2=Tobias |last3=von Mering |first3=Christian |last4=Creevey |first4=Christopher J. |last5=Snel |first5=Berend |last6=Bork |first6=Peer |s2cid=1615592 |author-link6=Peer Bork |date=3 March 2006 |title=Toward Automatic Reconstruction of a Highly Resolved Tree of Life |journal=Science |volume=311 |issue=5765 |pages=1283–1287 |bibcode=2006Sci...311.1283C |doi=10.1126/science.1123061 |issn=0036-8075 |pmid=16513982 |display-authors=3 |url=http://bioinformatics.bio.uu.nl/pdf/Ciccarelli.s06-311.pdf |url-status=live |archive-url=https://web.archive.org/web/20160304035346/http://bioinformatics.bio.uu.nl/pdf/Ciccarelli.s06-311.pdf |archive-date=4 March 2016 |citeseerx=10.1.1.381.9514}}</ref> The three [[Domain (biology)|domains]] are coloured, with bacteria blue, [[archaea]] green and [[eukaryote]]s red.}}
Prokaryotes inhabited the Earth from approximately 3–4&nbsp;billion years ago.<ref name="Cavalier-Smith-2006">{{cite journal |last=Cavalier-Smith |first=Thomas |author-link=Thomas Cavalier-Smith |date=29 June 2006 |title=Cell evolution and Earth history: stasis and revolution |journal=Philosophical Transactions of the Royal Society B |volume=361 |issue=1470 |pages=969–1006 |doi=10.1098/rstb.2006.1842 |issn=0962-8436 |pmc=1578732 |pmid=16754610}}</ref><ref>{{cite journal |last=Schopf |first=J. William |date=29 June 2006 |title=Fossil evidence of Archaean life |journal=Philosophical Transactions of the Royal Society B |volume=361 |issue=1470 |pages=869–885 |doi=10.1098/rstb.2006.1834 |pmc=1578735 |pmid=16754604}}
* {{cite journal |last1=Altermann |first1=Wladyslaw |last2=Kazmierczak |first2=Józef |date=November 2003 |title=Archean microfossils: a reappraisal of early life on Earth |journal=Research in Microbiology |volume=154 |issue=9 |pages=611–617 |doi=10.1016/j.resmic.2003.08.006 |pmid=14596897 |ref=none |doi-access=free}}</ref> No obvious changes in morphology or cellular organisation occurred in these organisms over the next few billion years.<ref>{{cite journal |last=Schopf |first=J. William |date=19 July 1994 |title=Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic |journal=PNAS |volume=91 |issue=15 |pages=6735–6742 |bibcode=1994PNAS...91.6735S |doi=10.1073/pnas.91.15.6735 |pmc=44277 |pmid=8041691 |doi-access=free}}</ref> The eukaryotic cells emerged between 1.6 and 2.7&nbsp;billion years ago. The next major change in cell structure came when bacteria were engulfed by eukaryotic cells, in a cooperative association called [[endosymbiosis]].<ref name="Poole-2007">{{cite journal |last1=Poole |first1=Anthony M. |last2=Penny |first2=David |date=January 2007 |title=Evaluating hypotheses for the origin of eukaryotes |journal=BioEssays |volume=29 |issue=1 |pages=74–84 |doi=10.1002/bies.20516 |issn=0265-9247 |pmid=17187354}}</ref><ref name="Dyall-2004">{{cite journal |last1=Dyall |first1=Sabrina D. |last2=Brown |first2=Mark T. |last3=Johnson |first3=Patricia J. |s2cid=19424594 |author-link3=Patricia J. Johnson |date=9 April 2004 |title=Ancient Invasions: From Endosymbionts to Organelles |journal=Science |volume=304 |issue=5668 |pages=253–257 |bibcode=2004Sci...304..253D |doi=10.1126/science.1094884 |pmid=15073369}}</ref> The engulfed bacteria and the host cell then underwent coevolution, with the bacteria evolving into either mitochondria or [[hydrogenosome]]s.<ref>{{cite journal |last=Martin |first=William |date=October 2005 |title=The missing link between hydrogenosomes and mitochondria |journal=Trends in Microbiology |volume=13 |issue=10 |pages=457–459 |doi=10.1016/j.tim.2005.08.005 |pmid=16109488}}</ref> Another engulfment of [[cyanobacteria]]l-like organisms led to the formation of chloroplasts in algae and plants.<ref>{{cite journal |last1=Lang |first1=B. Franz |last2=Gray |first2=Michael W. |last3=Burger |first3=Gertraud |date=December 1999 |title=Mitochondrial genome evolution and the origin of eukaryotes |journal=[[Annual Review of Genetics]] |volume=33 |pages=351–397 |doi=10.1146/annurev.genet.33.1.351 |issn=0066-4197 |pmid=10690412}}
* {{cite journal |last=McFadden |first=Geoffrey Ian |date=1 December 1999 |title=Endosymbiosis and evolution of the plant cell |journal=Current Opinion in Plant Biology |volume=2 |issue=6 |pages=513–519 |doi=10.1016/S1369-5266(99)00025-4 |pmid=10607659 |bibcode=1999COPB....2..513M |ref=none}}</ref>

The history of life was that of the [[unicellular]] eukaryotes, prokaryotes and archaea until around 1.7&nbsp;billion years ago, when [[multicellular organism]]s began to appear, with [[cellular differentiation|differentiated cells]] performing specialised functions.<ref name="Bonner1999">{{cite journal |last=Bonner |first=John Tyler |author-link=John Tyler Bonner |date=7 January 1998 |title=The origins of multicellularity |journal=[[Integrative Biology]] |volume=1 |issue=1 |pages=27–36 |doi=10.1002/(SICI)1520-6602(1998)1:1<27::AID-INBI4>3.0.CO;2-6 |issn=1757-9694}}</ref> The [[evolution of multicellularity]] occurred in multiple independent events, in organisms as diverse as [[sponge]]s, [[brown algae]], cyanobacteria, [[slime moulds]] and [[myxobacteria]].<ref>{{cite journal |last=Kaiser |first=Dale |s2cid=18276422 |author-link=A. Dale Kaiser |date=December 2001 |title=Building a multicellular organism |journal=[[Annual Review of Genetics]] |volume=35 |pages=103–123 |doi=10.1146/annurev.genet.35.102401.090145 |issn=0066-4197 |pmid=11700279}}</ref> In January 2016, scientists reported that, about 800&nbsp;million years ago, a minor genetic change in a single molecule called GK-PID may have allowed organisms to go from a single cell organism to one of many cells.<ref name="Zimmer-2016">{{cite news |last=Zimmer |first=Carl |author-link=Carl Zimmer |title=Genetic Flip Helped Organisms Go From One Cell to Many |url=https://www.nytimes.com/2016/01/12/science/genetic-flip-helped-organisms-go-from-one-cell-to-many.html |date=7 January 2016 |newspaper=The New York Times |issn=0362-4331 |access-date=7 January 2016 |url-status=live |archive-url=https://web.archive.org/web/20160107204432/http://www.nytimes.com/2016/01/12/science/genetic-flip-helped-organisms-go-from-one-cell-to-many.html |archive-date=7 January 2016}}</ref>

Approximately 538.8&nbsp;million years ago, a remarkable amount of biological diversity appeared over a span of around 10&nbsp;million years in what is called the [[Cambrian explosion]]. Here, the majority of [[Phylum|types]] of modern animals appeared in the fossil record, as well as unique lineages that subsequently became extinct.<ref name="Valentine-1999">{{cite journal |last1=Valentine |first1=James W. |author-link1=James W. Valentine |last2=Jablonski |first2=David |last3=Erwin |first3=Douglas H. |author-link3=Douglas Erwin |date=1 March 1999 |title=Fossils, molecules and embryos: new perspectives on the Cambrian explosion |url=http://dev.biologists.org/content/126/5/851.full.pdf+html |journal=[[Development (journal)|Development]] |volume=126 |issue=5 |pages=851–859 |doi=10.1242/dev.126.5.851 |issn=0950-1991 |pmid=9927587 |access-date=30 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20150301063309/http://dev.biologists.org/content/126/5/851.full.pdf+html |archive-date=1 March 2015|url-access=subscription }}</ref> Various triggers for the Cambrian explosion have been proposed, including the accumulation of oxygen in the atmosphere from photosynthesis.<ref>{{cite journal |last=Ohno |first=Susumu |s2cid=21879320 |date=January 1997 |title=The reason for as well as the consequence of the Cambrian explosion in animal evolution |journal=Journal of Molecular Evolution |volume=44 |issue=Suppl. 1 |pages=S23–S27 |doi=10.1007/PL00000055 |issn=0022-2844 |pmid=9071008 |bibcode=1997JMolE..44S..23O}}
* {{cite journal |last1=Valentine |first1=James W. |last2=Jablonski |first2=David |title=Morphological and developmental macroevolution: a paleontological perspective |url=http://www.ijdb.ehu.es/web/paper.php?doi=14756327 |year=2003 |journal=The International Journal of Developmental Biology |volume=47 |issue=7–8 |pages=517–522 |issn=0214-6282 |pmid=14756327 |access-date=30 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20141024234611/http://www.ijdb.ehu.es/web/paper.php?doi=14756327 |archive-date=24 October 2014 |ref=none}}</ref>

About 500&nbsp;million years ago, plants and fungi colonised the land and were soon followed by arthropods and other animals.<ref>{{cite journal |last=Waters |first=Elizabeth R. |date=December 2003 |title=Molecular adaptation and the origin of land plants |journal=[[Molecular Phylogenetics and Evolution]] |volume=29 |issue=3 |pages=456–463 |doi=10.1016/j.ympev.2003.07.018 |issn=1055-7903 |pmid=14615186 |bibcode=2003MolPE..29..456W}}</ref> Insects were particularly successful and even today make up the majority of animal species.<ref>{{cite journal |last=Mayhew |first=Peter J. |author-link=Peter Mayhew (biologist) |date=August 2007 |title=Why are there so many insect species? Perspectives from fossils and phylogenies |url=https://archive.org/details/sim_biological-reviews_2007-08_82_3/page/425 |journal=Biological Reviews |volume=82 |issue=3 |pages=425–454 |doi=10.1111/j.1469-185X.2007.00018.x |issn=1464-7931 |pmid=17624962 |s2cid=9356614}}</ref> [[Amphibian]]s first appeared around 364&nbsp;million years ago, followed by early [[amniote]]s and birds around 155&nbsp;million years ago (both from "reptile"-like lineages), [[mammal]]s around 129&nbsp;million years ago, [[Homininae]] around 10&nbsp;million years ago and [[Anatomically modern humans|modern humans]] around 250,000 years ago.<ref>{{cite journal |last=Carroll |first=Robert L. |author-link=Robert L. Carroll |date=May 2007 |title=The Palaeozoic Ancestry of Salamanders, Frogs and Caecilians |journal=[[Zoological Journal of the Linnean Society]] |volume=150 |issue=Supplement s1 |pages=1–140 |doi=10.1111/j.1096-3642.2007.00246.x |issn=1096-3642 |doi-access=free}}</ref><ref>{{cite journal |last1=Wible |first1=John R. |last2=Rougier |first2=Guillermo W. |last3=Novacek |first3=Michael J. |last4=Asher |first4=Robert J. |date=21 June 2007 |title=Cretaceous eutherians and Laurasian origin for placental mammals near the K/T boundary |url=https://archive.org/details/sim_nature-uk_2007-06-21_447_7147/page/1003 |journal=Nature |volume=447 |issue=7147 |pages=1003–1006 |bibcode=2007Natur.447.1003W |doi=10.1038/nature05854 |issn=0028-0836 |pmid=17581585 |s2cid=4334424}}</ref><ref>{{cite journal |last=Witmer |first=Lawrence M. |s2cid=205066360 |author-link=Lawrence Witmer |date=28 July 2011 |title=Palaeontology: An icon knocked from its perch |journal=Nature |volume=475 |issue=7357 |pages=458–459 |doi=10.1038/475458a |issn=0028-0836 |pmid=21796198}}</ref> However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both biomass and species being prokaryotes.<ref name="Schloss-2004" />