Editing Cell (biology) (section)

== Origins ==<!-- This section is linked from [[Timeline of evolution]] -->

{{main|Evolutionary history of life}}

The origin of cells has to do with the [[Abiogenesis|origin of life]], which began the [[timeline of evolution|history of life]] on Earth.

=== Origin of life ===

{{further|Abiogenesis|Evolution of cells}}

[[File:Stromatolites.jpg|thumb|[[Stromatolites]] are left behind by [[cyanobacteria]], also called blue-green algae. They are among the oldest fossils of life on Earth. This one-billion-year-old fossil is from [[Glacier National Park (U.S.)|Glacier National Park]] in the United States.]]

Small molecules needed for life may have been carried to Earth on meteorites, created at [[Hydrothermal vent|deep-sea vents]], or [[Miller–Urey experiment|synthesized by lightning in a reducing atmosphere]]. There is little experimental data defining what the first self-replicating forms were. [[RNA]] may have been [[RNA world hypothesis|the earliest self-replicating molecule]], as it can both store genetic information and catalyze chemical reactions.<ref name=OrgelLE>{{cite journal |last= Orgel |first=L. E. |title=The origin of life--a review of facts and speculations |journal=Trends in Biochemical Sciences |volume=23 |issue=12 |pages=491–495 |date=December 1998 |pmid=9868373 |doi=10.1016/S0968-0004(98)01300-0 }}</ref>

Cells emerged around 4 billion years ago.<ref name="NAT-20170301">{{cite journal |last1=Dodd |first1=Matthew S. |last2=Papineau |first2=Dominic |last3=Grenne |first3=Tor |last4=Slack |first4=John F. |last5=Rittner |first5=Martin |last6=Pirajno |first6=Franco |last7=O'Neil |first7=Jonathan |last8=Little |first8=Crispin T.S. |display-authors=3 |title=Evidence for early life in Earth's oldest hydrothermal vent precipitates |journal=[[Nature (journal)|Nature]] |date=1 March 2017 |volume=543 |issue=7643 |pages=60–64 |doi=10.1038/nature21377 |doi-access=free |pmid=28252057 |bibcode=2017Natur.543...60D |url=http://eprints.whiterose.ac.uk/112179/ |access-date=2 March 2017 |url-status=live |archive-url=https://web.archive.org/web/20170908201821/http://eprints.whiterose.ac.uk/112179/ |archive-date=8 September 2017}}</ref><ref>{{Cite journal |last1=Betts |first1=Holly C. |last2=Puttick |first2=Mark N. |last3=Clark |first3=James W. |last4=Williams |first4=Tom A. |last5=Donoghue |first5=Philip C. J. |last6=Pisani |first6=Davide |date=20 August 2018 |title=Integrated genomic and fossil evidence illuminates life's early evolution and eukaryote origin |journal=Nature Ecology & Evolution |volume=2 |issue=10 |pages=1556–1562 |doi=10.1038/s41559-018-0644-x |pmid=30127539|pmc=6152910 |bibcode=2018NatEE...2.1556B }}</ref> The first cells were most likely [[heterotroph]]s. The early cell membranes were probably simpler and more permeable than modern ones, with only a single fatty acid chain per lipid. Lipids spontaneously form bilayered [[Vesicle (biology and chemistry)|vesicles]] in water, and could have preceded RNA.<ref name="Griffiths 2007">{{cite journal |last=Griffiths |first=G. |title=Cell evolution and the problem of membrane topology |journal=Nature Reviews. Molecular Cell Biology |volume=8 |issue=12 |pages=1018–1024 |date=December 2007 |pmid=17971839 |doi=10.1038/nrm2287 |s2cid=31072778 |doi-access=free }}</ref><ref name="ScienceDaily 2021">{{cite web |title=First cells may have emerged because building blocks of proteins stabilized membranes |url=https://www.sciencedaily.com/releases/2019/08/190812155502.htm |access-date=2021-09-18 |website=ScienceDaily |archive-date=2021-09-18 |archive-url=https://web.archive.org/web/20210918102211/https://www.sciencedaily.com/releases/2019/08/190812155502.htm |url-status=live }}</ref>

=== First eukaryotic cells ===

{{main|Eukaryogenesis}}

[[File:Symbiogenesis 2 mergers.svg|thumb|upright=1.35|In the theory of [[symbiogenesis]], a merger of an [[archaea]]n and an aerobic bacterium created the eukaryotes, with aerobic [[Mitochondrion|mitochondria]], some 2.2 billion years ago. A second merger, 1.6 billion years ago, added [[chloroplast]]s, creating the green plants.<ref name=latorre/>]]

[[Eukaryote|Eukaryotic]] cells were created some 2.2 billion years ago in a process called [[eukaryogenesis]]. This is widely agreed to have involved [[symbiogenesis]], in which [[archaea]] and [[bacteria]] came together to create the first eukaryotic common ancestor. This cell had a new level of complexity and capability, with a nucleus<ref name="McGrath 2022">{{cite journal |last=McGrath |first=Casey |title=Highlight: Unraveling the Origins of LUCA and LECA on the Tree of Life |journal=Genome Biology and Evolution |volume=14 |issue=6 |date=31 May 2022 |pages=evac072 |doi=10.1093/gbe/evac072|pmc=9168435 }}</ref><ref name="Weiss et al 2016">{{cite journal |last1=Weiss |first1=Madeline C. |last2=Sousa |first2=F. L. |last3=Mrnjavac |first3=N. |last4=Neukirchen |first4=S. |last5=Roettger |first5=M. |last6=Nelson-Sathi |first6=S. |last7=Martin |first7=William F. |author7-link=William F. Martin |display-authors=3 |s2cid=2997255 |year=2016 |title=The physiology and habitat of the last universal common ancestor |journal=Nature Microbiology |volume=1 |issue=9 |page=16116 |doi=10.1038/nmicrobiol.2016.116 |pmid=27562259 |url=http://complexityexplorer.s3.amazonaws.com/supplemental_materials/3.6+Early+Metabolisms/Weiss_et_al_Nat_Microbiol_2016.pdf }}</ref> and facultatively aerobic [[Mitochondrion|mitochondria]].<ref name=latorre>{{cite book |last1=Latorre |first1=A. |last2=Durban |first2=A |last3=Moya |first3=A. |last4=Pereto |first4=J. |chapter-url=https://books.google.com/books?id=m3oFebknu1cC&pg=PA326 |chapter=The role of symbiosis in eukaryotic evolution |title=Origins and Evolution of Life: An astrobiological perspective |editor1=Gargaud, Muriel |editor2=López-Garcìa, Purificacion |editor3=Martin, H. |year=2011 |location=Cambridge |publisher=Cambridge University Press |pages=326–339 |isbn=978-0-521-76131-4 |access-date=27 August 2017 |archive-date=24 March 2019 |archive-url=https://web.archive.org/web/20190324055723/https://books.google.com/books?id=m3oFebknu1cC&pg=PA326 |url-status=live }}</ref> It evolved some 2 billion years ago into a population of single-celled organisms that included the last eukaryotic common ancestor, gaining capabilities along the way, though the sequence of the steps involved has been disputed, and may not have started with symbiogenesis. It featured at least one [[centriole]] and [[cilium]], sex ([[meiosis]] and [[syngamy]]), [[peroxisome]]s, and a dormant [[cyst]] with a cell wall of [[chitin]] and/or [[cellulose]].<ref>{{cite journal |last=Leander |first=B. S. |title=Predatory protists |journal=Current Biology |volume=30 |issue=10 |pages=R510–R516 |date=May 2020 |pmid=32428491 |doi=10.1016/j.cub.2020.03.052 |s2cid=218710816 |doi-access=free }}</ref><ref name="Strassert Irisarri Williams Burki 2021">{{cite journal |last1=Strassert |first1=Jürgen F. H. |last2=Irisarri |first2=Iker |last3=Williams |first3=Tom A. |last4=Burki |first4=Fabien |title=A molecular timescale for eukaryote evolution with implications for the origin of red algal-derived plastids |journal=Nature Communications |volume=12 |issue=1 |date=25 March 2021 |page=1879 |doi=10.1038/s41467-021-22044-z|pmid=33767194 |pmc=7994803 |bibcode=2021NatCo..12.1879S }}</ref> In turn, the last eukaryotic common ancestor gave rise to the eukaryotes' [[crown group]], containing the ancestors of [[animal]]s, [[Fungus|fungi]], [[plant]]s, and a diverse range of single-celled organisms.<ref name="Gabaldón">{{cite journal |last=Gabaldón |first=T. |title=Origin and Early Evolution of the Eukaryotic Cell |journal=Annual Review of Microbiology |volume=75 |issue=1 |pages=631–647 |date=October 2021 |pmid=34343017 |doi=10.1146/annurev-micro-090817-062213 |s2cid=236916203 }}</ref><ref name="w1990">{{cite journal |last1=Woese |first1=C.R. |author1-link=Carl Woese |last2=Kandler |first2=Otto |author2-link=Otto Kandler |last3=Wheelis |first3=Mark L. |author3-link=Mark Wheelis |title=Towards a natural system of organisms: proposal for the domains Archaea, Bacteria, and Eucarya |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=87 |issue=12 |pages=4576–4579 |date=June 1990 |pmid=2112744 |pmc=54159 |doi=10.1073/pnas.87.12.4576 |bibcode=1990PNAS...87.4576W |doi-access=free }}</ref> The plants were created around 1.6 billion years ago with a second episode of symbiogenesis that added [[chloroplast]]s, derived from [[cyanobacteria]].<ref name=latorre/>