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ANTH 105 - EXAM 3 Material: WK 13 11/26 + WK 14 12/3-12/5 + WK 15 12/10-12/12

Terms in this set (44)

The two ideas are the savanna hypothesis and the pre-adaptation hypothesis.

OK, I'm going to go into a bit more detail than I had time for in class. When Lucy (Australopithecus afarensis) was discovered in Ethiopia 1974 it was clear she was a biped. The geologic evidence also suggested there had been some changes in the ecology of East Africa in the time period from when Lucy's species was discovered, about 3-4 million years ago. Earlier periods in geology suggest East Africa had shifted from a forested environment to more of a savanna (grasslands) one. Therefore, it was suggested that quadrupedal apes evolved to walk upright because there were advantages to being a biped on a savanna compared to a forest (be sure to check the notes to remind yourself what those advantages were).
This hypothesis made sense for a while, until older hominins were discovered in the early 2000s, such as Orrorin and Sahelanthropus, dating back from 6 to 7 mya. These species showed anatomical clues that they were bipedal, but this was before the forests had shifted into grasslands. So this required a re-evaluation of the older savanna hypothesis. Why were hominins walking bipedally in a primarily forested environment? One clue might come from orangutans and other apes who don't walk bipedally much on the ground today, but are fairly good at it on branches in the trees. We aren't descended from modern orangutans, but the newer hypothesis (the pre-adaptation hypothesis) then became: well, maybe it was possible that some apes adapted to bipedalism in the trees first, and then later some of them took that type of locomotion to the ground once the savannas opened up. All of the same benefits would have applied as in the savnna idea (again, see the notes), only the timeline needed revision.