Editing Pan (genus) (section)

==Anatomy and physiology==
{{Multiple image |header= |caption_align=center |align=left |width= |direction=horizontal |image1=Man&chimpbrains.png |caption1=Human and chimpanzee skulls and brains (not to scale), as illustrated in [[Paul Gervais|Gervais]]' ''Histoire naturelle des mammifères'' |width1=200 |image2=Chimpanzee and human brain scaled to the same size Thomas Henry Huxley.png |caption2=The chimpanzee's brain on the left and the human brain on the right have been scaled to the same size to show the relative proportions of their parts. These drawings were in a book made in 1904 by [[Thomas Henry Huxley]].<ref>{{cite book |last=Huxley |first=T. H. |year=1904 |hdl=2027/uva.x000705538 |url=https://babel.hathitrust.org/cgi/pt?id=uva.x000705538&view=1up&seq=98&skin=2021&q1=brain |title=Man's Place in Nature |series=The new science library, v. 5 |pages=78 |publisher=J. A. Hill and Company}}</ref> |width2=320 |footer= }}
The chimpanzee's arms are longer than its legs. The male common chimp stands up to {{convert|1.2|m|ft|abbr=on}} high. Male adult wild chimps weigh between 40 and 60&nbsp;kg<ref>{{Cite journal |last1=Uehara |first1=S. |last2=Nishida |first2=T. |date=March 1, 1987 |title=Body weights of wild chimpanzees (''Pan troglodytes schweinfurthii'') of the Mahale Mountains National Park, Tanzania |journal=American Journal of Physical Anthropology |volume=72 |issue=3 |pages=315–321 |doi=10.1002/ajpa.1330720305 |issn=0002-9483 |pmid=3578495}}</ref><ref name=":0">{{Cite book |title=Jane Goodall: Primatologist and Animal Activist |last=Jankowski |first=C. |publisher=Compass Point Books |year=2009 |isbn=9780756540548 |location=Mankato, MN, USA |pages=14 |oclc=244481732}}</ref><ref>{{Cite news |url=http://www.nationalgeographic.com/animals/mammals/c/chimpanzee/ |archive-url=https://web.archive.org/web/20161018065027/http://www.nationalgeographic.com/animals/mammals/c/chimpanzee/ |url-status=dead |archive-date=October 18, 2016 |title=Chimpanzee |date=May 10, 2011 |work=nationalgeographic.com |access-date=2017-03-21 |publisher=National Geographic}}</ref> with females weighing between 27 and 50&nbsp;kg.<ref name=":0" /> When extended, the common chimp's long arms span one and a half times the body's height.<ref name="Shefferly2005"/> The bonobo is slightly shorter and thinner than the common chimpanzee, but has longer limbs. In trees, both species climb with their long, powerful arms; on the ground, chimpanzees usually [[knuckle-walking|knuckle-walk]], or walk on all fours, clenching their fists and supporting themselves on the knuckles. Chimpanzees are better suited for walking than orangutans, because the chimp's feet have broader soles and shorter toes. The bonobo has proportionately longer upper limbs and walks upright more often than does the common chimpanzee. Both species can walk upright on two legs when carrying objects with their hands and arms.

[[File:Comparison of size of chimpanzee (Pan troglodytes) and human.svg|thumb|Comparison of size of adult chimpanzee and adult human.]]
The chimpanzee is tailless; its coat is dark; its face, fingers, palms of the hands, and soles of the feet are hairless. The exposed skin of the face, hands, and feet varies from pink to very dark in both species, but is generally lighter in younger individuals and darkens with maturity. A University of Chicago Medical Centre study has found significant genetic differences between chimpanzee populations.<ref>{{Cite news |title=Gene study shows three distinct groups of chimpanzees |date=April 20, 2007 |url=http://www.eurekalert.org/pub_releases/2007-04/uocm-gss042007.php |work=EurekAlert |access-date=2007-04-23 }}</ref> A bony shelf over the eyes gives the forehead a receding appearance, and the nose is flat. Although the jaws protrude, a chimp's lips are thrust out only when it pouts.

The brain of a chimpanzee has been measured at a general range of 282–500&nbsp;cm<sup>3</sup>.<ref>{{cite book |author=Tobias, P. |year=1971 |url=https://archive.org/details/braininhominidev38tobi |title=The Brain in Hominid Evolution |location=New York, USA |publisher=Columbia University Press |hdl=2246/6020|isbn=9780231035187 }}{{cite thesis |author=Schoenemann, P. T. |year=1997 |url=http://www.indiana.edu/~brainevo/publications/dissertation/Dissertation_title.htm |title=An MRI study of the relationship between human neuroanatomy and behavioral ability |type=PhD thesis |publisher=University of California, Berkeley}}</ref> The human brain, in contrast, is about three times larger, with a reported average volume of about 1330&nbsp;cm<sup>3</sup>.<ref>{{cite journal |doi=10.1146/annurev.anthro.35.081705.123210 |title=Evolution of the size and functional areas of the human brain |year=2006 |last1=Schoenemann |first1=P. T. |journal=Annual Review of Anthropology |volume=35 |pages=379–406 |issue=1 |quote=Modern human brain sizes vary widely, but average ~1330 cc (Dekaban 1978, Garby ''et al.'' 1993, Ho ''et al.'' 1980a, Pakkenberg & Voigt 1964)}}</ref>

{{Anchor|Testicles}}
Chimpanzees reach [[puberty]] between the age of eight and ten years.<ref>{{Cite book| url=https://oxfordre.com/psychology/display/10.1093/acrefore/9780190236557.001.0001/acrefore-9780190236557-e-50 | doi=10.1093/acrefore/9780190236557.013.50 | chapter=Cognitive Development in Chimpanzees | title=Oxford Research Encyclopedia of Psychology | date=2021 | last1=Matsuzawa | first1=Tetsuro | isbn=978-0-19-023655-7 }}</ref> A chimpanzee's [[testicle]]s are unusually large for its body size, with a combined weight of about {{convert|4|oz|abbr=on}} compared to a gorilla's {{convert|1|oz|abbr=on}} or a human's {{convert|1.5|oz}}. This relatively great size is generally attributed to [[sperm competition]] due to the [[Polygynandry|polygynandrous]] nature of chimpanzee [[Animal sexual behaviour|mating behaviour]].<ref name=rat_behavior>{{cite web |url=http://www.ratbehavior.org/testicles.htm |work=ratbehavior.org |title=Why are rat testicles so big? |date=2003–2004 |access-date=September 1, 2009}}</ref><ref>{{cite web |last1=Maslin |first1=M. |title=Why did humans evolve big penises but small testicles? |url=http://theconversation.com/why-did-humans-evolve-big-penises-but-small-testicles-71652 |website=theconversation.com |access-date=22 December 2018 |date=25 January 2017}}</ref> Unlike gorillas, chimpanzees and bonobos have long and filiform [[Penis|penises]] without a [[Glans penis|glans]].<ref>{{Cite book |last=Dixson |first=Alan F. |url=https://www.google.com/books/edition/Sexual_Selection_and_the_Origins_of_Huma/x4hNEAAAQBAJ?hl=en&gbpv=1&pg=PA68&printsec=frontcover |title=Sexual Selection and the Origins of Human Mating Systems |date=2009-05-14 |publisher=Oxford University Press |isbn=978-0-19-955943-5 |language=en}}</ref>