Editing Homo habilis (section)

==Anatomy==
===Skull===
[[File:Homo habilis - forensic facial reconstruction.png|thumb|left|upright|''Homo habilis'' – forensic facial reconstruction]]
It has generally been thought that brain size increased along the human line especially rapidly at the transition between species, with ''H. habilis'' brain size smaller than that of ''H. ergaster''&nbsp;/&nbsp;''H. erectus'', jumping from about {{cvt|600–650|cc}} in ''H. habilis'' to about {{cvt|900–1000|cc}} in ''H. ergaster'' and ''H. erectus''.<ref name=Spoor2015/><ref name=Tobias1987/> However, a 2015 study showed that the brain sizes of ''H. habilis'', ''H. rudolfensis'', and ''H. ergaster'' generally ranged between {{cvt|500–900|cc}} after reappraising the brain volume of OH 7 from {{cvt|647–687|cc}} to {{cvt|729–824|cc}}.<ref name=Spoor2015/> This does, nonetheless, indicate a jump from australopithecine brain size which generally ranged from {{cvt|400–500|cc}}.<ref name=Tobias1987>{{cite journal|first=P. V.|last=Tobias|year=1987|title=The brain of ''Homo habilis'': A new level of organization in cerebral evolution|journal=Journal of Human Evolution|volume=16|issue=7–8|pages=741–761|doi=10.1016/0047-2484(87)90022-4}}</ref>
{{Human timeline}}
The brain anatomy of all ''Homo'' features an expanded [[cerebrum]] in comparison to australopithecines. The pattern of striations on the teeth of OH 65 slant right, which may have been accidentally self-inflicted when the individual was pulling a piece of meat with its teeth and the left hand while trying to cut it with a stone tool using the right hand. If correct, this could indicate right [[handedness]], and handedness is associated with major reorganisation of the brain and the [[lateralisation of brain function]] between the left and right hemispheres. This scenario has also been hypothesised for some Neanderthal specimens. Lateralisation could be implicated in tool use. In modern humans, lateralisation is weakly associated with language.<ref>{{cite journal|first1=D. W.|last1=Frayer|first2=R. J.|last2=Clarke|first3=I.|last3=Fiore|display-authors=et al.|year=2016|title=OH-65: The earliest evidence for right-handedness in the fossil record|journal=Journal of Human Evolution|volume=100|pages=65–72|doi=10.1016/j.jhevol.2016.07.002|pmid=27765150}}</ref>

The tooth rows of ''H. habilis'' were V-shaped as opposed to U-shaped in later ''Homo'', and the mouth jutted outwards (was [[prognathic]]), though the face was flat from the nose up.<ref name=Spoor2015>{{cite journal |author1=F. Spoor |author2=P. Gunz |author3=S. Neubauer |author4=S. Stelzer |author5=N. Scott |author6=A. Kwekason |author7=M. C. Dean | year = 2015 | title = Reconstructed ''Homo habilis'' type OH 7 suggests deep-rooted species diversity in early ''Homo'' | journal = Nature | volume = 519 |issue= 7541 | pages =83–86 | doi= 10.1038/nature14224 | pmid=25739632 | bibcode=2015Natur.519...83S|s2cid=4470282 }}</ref>

===Build===
Based on the fragmentary skeletons OH 62 (presumed female) and KNM-ER 3735 (presumed male), ''H. habilis'' body anatomy has generally been considered to have been more apelike than even that of the earlier ''A. afarensis''; this is consistent with an at least partially [[arboreal]] lifestyle in the trees as is assumed in australopithecines. Based on OH 62 and assuming comparable body dimensions to australopithecines, ''H. habilis'' has generally been interpreted as having been small-bodied like australopithecines, with OH 62 generally estimated at {{cvt|100–120|cm|ftin}} in height and {{cvt|20–37|kg}} in weight. However, assuming longer, modern humanlike legs, OH 62 would have been about {{cvt|148|cm|ftin}} and {{cvt|35|kg}}, and KNM-ER 3735 about the same size.<ref>{{cite journal|first1=M.|last1=Will|first2=J. T.|last2=Stock|year=2015|title=Spatial and temporal variation of body size among early ''Homo''|journal=Journal of Human Evolution|volume=82|pages=15–33|doi=10.1016/j.jhevol.2015.02.009|pmid=25818180|doi-access=free}}</ref> For comparison, modern human men and women in the year 1900 averaged {{cvt|163|cm|ftin}} and {{cvt|152.7|cm|ft}}, respectively.<ref>{{cite journal|url=https://ourworldindata.org/human-height|first1=M.|last1=Roser|author1-link=Max Roser |first2=C.|last2=Appel|first3=H.|last3=Ritchie|author3-link=Hannah Ritchie |year=2013|title=Human Height|journal=Our World in Data|access-date=16 June 2020}}</ref> It is generally assumed that pre-''H. ergaster'' hominins, including ''H. habilis'', exhibited notable [[sexual dimorphism]] with males markedly bigger than females. However, relative female body mass is unknown in this species.<ref name=Ungar2006>{{cite journal|first1=P. S.|last1=Ungar|first2=F. E.|last2=Grine|year=2006|title=Diet in Early ''Homo'': A Review of the Evidence and a New Model of Adaptive Versatility|journal=Annual Review of Anthropology|volume=35|pages=208–228|doi=10.1146/annurev.anthro.35.081705.123153}}</ref>

Early hominins, including ''H. habilis'', are thought to have had thick body hair coverage like modern non-human apes because they appear to have inhabited colder regions and are thought to have had a less active lifestyle than (presumed hairless) post-''ergaster'' species. Consequently, they probably required thick body hair to stay warm.<ref>{{cite journal|first1=T.|last1=Dávid-Berrett|first2=R. I. M.|last2=Dunbar|year=2016|title=Bipedality and hair loss in human evolution revisited: The impact of altitude and activity scheduling|journal=Journal of Human Evolution|volume=94|pages=72–82|doi=10.1016/j.jhevol.2016.02.006|pmid=27178459|pmc=4874949}}</ref> Based on dental development rates, ''H. habilis'' is assumed to have had an accelerated growth rate compared to modern humans, more like that of modern non-human apes.<ref>{{cite journal|first=G. T.|last=Schwartz|year=2012|title=Growth, Development, and Life History throughout the Evolution of ''Homo''|journal=Current Anthropology|volume=53|issue=6|pages=400–401|doi=10.1086/667591|s2cid=84537505}}</ref>

===Limbs===
[[File:Olduvai Hominin 8.jpg|thumb|left|upright=1.3|OH 8, bearing crocodile tooth marks]]
The arms of ''H. habilis'' and australopithecines have generally been considered to have been proportionally long and so adapted for climbing and swinging.<ref>{{cite journal|first1=M.|last1=Haeusler|first2=H.|last2=McHenry|year=2007|title=Evolutionary reversals of limb proportions in early hominids? evidence from KNM-ER 3735 (''Homo habilis'')|journal=Journal of Human Evolution|volume=53|issue=4|pages=385–405|doi=10.1016/j.jhevol.2007.06.001|pmid=17688910}}</ref><ref>{{Cite journal|date=21 May 1987|author1=Donald C. Johanson |author2=Fidelis T. Masao |author3=Gerald G. Eck |author4=Tim D. White |author5=Robert C. Walter |author6=William H. Kimbel |author7=Berhane Asfaw |author8=Paul Manega |author9=Prosper Ndessokia |author10=Gen Suwa |title=New partial skeleton of ''Homo habilis'' from Olduvai Gorge, Tanzania |journal=Nature |volume=327 |pages=205–209 |doi=10.1038/327205a0 |pmid=3106831 |issue=6119 |bibcode=1987Natur.327..205J |s2cid=4321698 }}</ref><ref>{{Cite journal|year=1987|author=Wood, B. |title=Who is the 'real' ''Homo habilis''?|journal=Nature |volume=327 |pages=187–188 |doi= 10.1038/327187a0 |pmid=3106828 |issue=6119|bibcode=1987Natur.327..187W |s2cid=4329573 }}</ref> In 2004, anthropologists Martin Haeusler and [[Henry McHenry (anthropologist)|Henry McHenry]] argued that, because the [[humerus]] to [[femur]] ratio of OH 62 is within the range of variation for modern humans, and KNM-ER 3735 is close to the modern human average, it is unsafe to assume apelike proportions. Nonetheless, the humerus of OH 62 measured {{cvt|258–270|mm}} long and the [[ulna]] (forearm) {{cvt|245–255|mm}}, which is closer to the proportion seen in chimpanzees. The hand bones of OH 7 suggest precision gripping, important in dexterity, as well as adaptations for climbing. In regard to the femur, traditionally comparisons with the ''A. afarensis'' specimen AL 288-1 have been used to reconstruct stout legs for ''H. habilis'', but Haeusler and McHenry suggested the more gracile OH 24 femur (either belonging to ''H. ergaster''&nbsp;/&nbsp;''H. erectus'' or ''P. boisei'') may be a more apt comparison. In this instance, ''H. habilis'' would have had longer, humanlike legs and have been effective long-distance travellers as is assumed to have been the case in ''H. ergaster''.<ref name=Haeusler2004>{{cite journal|title=Body Proportions of ''Homo Habilis''|first1=M.|last1=Haeusler|first2=H. M.|last2=McHenry|journal=Journal of Human Evolution|volume=46|issue=4|pages=433–465|year=2004|doi=10.1016/j.jhevol.2004.01.004|pmid=15066379}}</ref> However, estimating the unpreserved length of a fossil is highly problematic. The thickness of the limb bones in OH 62 is more similar to chimpanzees than ''H. ergaster''&nbsp;/&nbsp;''H. erectus'' and modern humans, which may indicate different load bearing capabilities more suitable for arboreality in ''H. habilis''.<ref>{{cite journal|first=C.|last=Ruff|year=2009|title=Relative Limb Strength and Locomotion in ''Homo habilis''|journal=American Journal of Physical Anthropology|volume=138|issue=1|pages=90–100|doi=10.1002/ajpa.20907|pmid=18711733}}</ref> The strong [[fibula]] of OH 35 (though this may belong to ''P. boisei'') is more like that of non-human apes, and consistent with arboreality and vertical climbing.<ref>{{cite journal|first1=D.|last1=Marchi|first2=C. M.|last2=Harper|first3=H.|last3=Chirchir|first4=C. B.|last4=Ruff|year=2019|title=Relative fibular strength and locomotor behavior in KNM-WT 15000 and OH 35|journal=Journal of Human Evolution|volume=131|pages=48–60|doi=10.1016/j.jhevol.2019.02.005|pmid=31182206|hdl=11568/994382 |s2cid=145846013|hdl-access=free}}</ref>

[[Olduvai Hominid 8|OH 8]], a foot, is better suited for terrestrial movement than the foot of ''A. afarensis'', though it still retains many apelike features consistent with climbing.<ref name=Haeusler2004/> However, the foot has projected toe bone and compacted mid-foot joint structures, which restrict rotation between the foot and ankle as well as at the front foot. Foot stability enhances the efficiency of force transfer between the leg and the foot and vice versa, and is implicated in the [[plantar arch]] elastic spring mechanism which generates energy while running (but not walking). This could possibly indicate ''H. habilis'' was capable of some degree of [[Endurance running hypothesis|endurance running]], which is typically thought to have evolved later in ''H. ergaster''&nbsp;/&nbsp;''H. erectus''.<ref>{{cite journal|last1=Bramble|first1=D.|last2=Lieberman|first2=D.|title=Endurance running and the evolution of Homo|journal=Nature|year=2004|volume=432|issue=7015|doi=10.1038/nature03052|pmid=15549097|pages=345–352|bibcode=2004Natur.432..345B|s2cid=2470602|url=http://doc.rero.ch/record/15289/files/PAL_E2588.pdf }}</ref>