Editing Bipedalism (section)

===Savannah-based theory===
{{main|Savannah hypothesis}}
According to the Savanna-based theory, [[hominines]] came down from the tree's branches and adapted to life on the savanna by walking erect on two feet. The theory suggests that early hominids were forced to adapt to bipedal locomotion on the open savanna after they left the trees. One of the proposed mechanisms was the knuckle-walking hypothesis, which states that human ancestors used quadrupedal locomotion on the savanna, as evidenced by morphological characteristics found in ''Australopithecus anamensis'' and ''Australopithecus afarensis'' forelimbs, and that it is less parsimonious to assume that knuckle walking developed twice in genera ''[[Pan (genus)|Pan]]'' and ''[[Gorilla (genus)|Gorilla]]'' instead of evolving it once as [[synapomorphy]] for ''Pan'' and ''Gorilla'' before losing it in Australopithecus.<ref>{{Cite journal |last1=Richmond |first1=B. G. |last2=Strait |first2=D. S. |year=2000 |title=Evidence that humans evolved from a knuckle-walking ancestor |journal=Nature |volume=404 |issue=6776 |pages=382–385 |doi=10.1038/35006045 |pmid=10746723 |bibcode=2000Natur.404..382R |s2cid=4303978}}</ref> The evolution of an orthograde posture would have been very helpful on a savanna as it would allow the ability to look over tall grasses in order to watch out for predators, or terrestrially hunt and sneak up on prey.<ref name="Dean, F 2000">Dean, F. 2000. Primate diversity. W.W. Norton & Company, Inc: New York. Print.</ref> It was also suggested in P. E. Wheeler's "The evolution of bipedality and loss of functional body hair in hominids", that a possible advantage of bipedalism in the savanna was reducing the amount of surface area of the body exposed to the sun, helping regulate body temperature.<ref>{{Cite journal |last1=Wheeler |first1=P. E. |year=1984 |title=The Evolution of Bipedality and Loss of Functional Body Hair in Hominoids |journal=Journal of Human Evolution |volume=13 |issue=1 |pages=91–98 |doi=10.1016/s0047-2484(84)80079-2|bibcode=1984JHumE..13...91W }}</ref> In fact, [[Elizabeth Vrba]]'s [[turnover-pulse hypothesis|turnover pulse hypothesis]] supports the savanna-based theory by explaining the shrinking of forested areas due to global warming and cooling, which forced animals out into the open grasslands and caused the need for hominids to acquire bipedality.<ref name="Sunset on the savanna">{{cite web |last=Shreeve |first=James |date=July 1996 |url=http://www.cabrillo.edu/~crsmith/Sunset.Savanna.doc |title=Sunset on the savanna |work=Discover |archive-url=https://web.archive.org/web/20170928010036/http://www.cabrillo.edu/~crsmith/Sunset.Savanna.doc |archive-date=2017-09-28}}</ref>

Others state hominines had already achieved the bipedal adaptation that was used in the savanna. The fossil evidence reveals that early bipedal hominins were still adapted to climbing trees at the time they were also [[walking]] upright.<ref>{{Cite journal |last1=Green, Alemseged |first1=David, Zeresenay |title=Australopithecus afarensis Scapular Ontogeny, Function, and the Role of Climbing in Human Evolution |journal=Science |date=2012 |volume=338 |issue=6106 |pages=514–517 |doi=10.1126/science.1227123|pmid=23112331 |bibcode=2012Sci...338..514G |s2cid=206543814}}</ref> It is possible that bipedalism evolved in the trees, and was later applied to the savanna as a vestigial trait. Humans and orangutans are both unique to a bipedal reactive adaptation when climbing on thin branches, in which they have increased hip and knee extension in relation to the diameter of the branch, which can increase an arboreal feeding range and can be attributed to a convergent evolution of bipedalism evolving in arboreal environments.<ref>{{Cite journal |last1=Thorpe |first1=S. K. |last2=Holder |first2=R. L. |last3=Crompton |first3=R. H. |year=2007 |title=Origin of human bipedalism as an adaptation for locomotion on flexible branches |doi=10.1126/science.1140799 |journal=Science |volume=316 |issue=5829 |pages=1328–31 |pmid=17540902| bibcode=2007Sci...316.1328T |s2cid=85992565}}</ref> Hominine fossils found in dry grassland environments led anthropologists to believe hominines lived, slept, walked upright, and died only in those environments because no hominine fossils were found in forested areas. However, fossilization is a rare occurrence—the conditions must be just right in order for an organism that dies to become fossilized for somebody to find later, which is also a rare occurrence. The fact that no hominine fossils were found in forests does not ultimately lead to the conclusion that no hominines ever died there. The convenience of the savanna-based theory caused this point to be overlooked for over a hundred years.<ref name="Sunset on the savanna"/>

Some of the fossils found actually showed that there was still an adaptation to arboreal life. For example, [[Lucy (Australopithecus)|Lucy]], the famous ''[[Australopithecus afarensis]]'', found in Hadar in Ethiopia, which may have been forested at the time of Lucy's death, had curved fingers that would still give her the ability to grasp tree branches, but she walked bipedally. "[[Little Foot]]", a nearly-complete specimen of ''[[Australopithecus africanus]]'', has a divergent big toe as well as the ankle strength to walk upright. "Little Foot" could grasp things using his feet like an ape, perhaps tree branches, and he was bipedal. Ancient pollen found in the soil in the locations in which these fossils were found suggest that the area used to be much more wet and covered in thick vegetation and has only recently become the arid desert it is now.<ref name="Sunset on the savanna"/>