That all sounds perfectly feasible. What surprised me was the chimpanzee foot he waved around; I guess I just never thought that their ankle [lower wrist] is habitually at about 90 deg.
The big question though, is whether the carrying of stick tools in the hand was the major reason for walking bipedally. I tend to think it was and that other aspects, like it takes less energy to balance on two legs was a helpful synergy rather than the main reason.
The habitual comparison with chimps and sometimes gorillas is not beneficial here, since they have both independently evolved knucklewalk locomotion (partly arboreal respectively all ground). Probably because of mass, as gibbons with or without arm use do a pretty similar bipedal locomotion between trees as we do. (There are interesting youtubes outside and inside walk labs.)
And both gibbons, if you take out their long arms and specialized ball wrist, and humans, if you take out their specialized feet, hips and large mass, are pretty generic monkeylike hominoids. I think we resisted specialization longer, but we got more able and interested in hunting-gathering (meat and roots) than the chimps (say) and that started it.
At first gathering roots and then get away from predators back into trees made bipedalism fitter. Tool carrying could have been later, as mobility increased and it was awkward to find or remake your digging (roots) and carving (root, carrion, fresh hunt) tools.
Maybe I shouldn't say we resisted specialization, as there are pretty clear signs that we socialized amiably early on, to the degree we rapidly lost large ape canines. AFAIK some have proposed that as definition for our Homo lineage.
Apparently we didn't go the bonobo route, but started to go for monogamous relationships and hidden estrous and less sexual dimorphism instead. Each to their own.
So that was perhaps our earliest specialization. Of course, loss of canines promoted fitness of later tool use! (Defensive or aggressive stones and sticks.)
A_Paradox
Jan 1, 2013The big question though, is whether the carrying of stick tools in the hand was the major reason for walking bipedally. I tend to think it was and that other aspects, like it takes less energy to balance on two legs was a helpful synergy rather than the main reason.