Language, opposable thumbs, and erect posture—those are the three keys to the kingdom: Doug Jones: Four Legs Good, Two Legs Better: "With Ardipithecus Radius (about 4.5 million years ago) we have the strongest evidence so far that hominins have adopted bipedalism.... Even... she had a somewhat diverging big toe, and arms and hands well-adapted for suspension, suggesting she was bipedal on the ground, but still spent a lot of time in trees.... Bipedalism allowed ancestral dinosaurs to overcome the tight coupling of locomotion and respiration that prevents sprawling lizards from breathing while they run. But human bipedalism, with no counterbalancing tail, is different. As far as we know it evolved only once...
...Human bipedalism is... related to tradeoffs in locomotion.... Other great apes pay a big price for being the largest animals well-adapted for moving around under and among branches: great ape locomotion on the ground is particularly inefficient. Chimpanzees spend several times as much energy knuckle-walking on all fours as you would expect based on comparisons to similar sized quadrupedal mammals.... Humans by contrast take a little less energy to walk around than a same-size four-legged mammal.... And a study that came out just last year shows that the same was true of Ardipithecus: she was an efficient bipedal walker.... That said, efficiency isn’t everything. Human beings are lousy at sprinting–try outsprinting your dog, or a squirrel....
It may be that bipedalism evolved initially in an environment where predation pressure wasn’t very intense, and the need for speed was not as great. This argument has been made for Oreopithecus, living on an island in the Mediterranean. Perhaps Graecopithecus initially enjoyed a similar isolation, and freedom from predation, associated in some way with the drying and flooding of the Mediterranean...
#noted
