Human evolution

I saw a documentary recently about paleontological work on "Ardipithecus Ramidus,"
and a skeleton of a particular female of that species found on a hill called Aramis.

The documentary was not at all well constructed -- it repeated its points endlessly -- still, it did challenge two conceptions I have long held about human evolution.

First, I have long bought into the idea that humans walk upright because of the grasslands of Africa. Quadrupeds in anything like our size would often have their faces buried in the tall grasses, unable to get a clear view of potential predators, or potential prey. Bipedelism, in that environment, would seem a real plus in the Darwinian competition for survival.

That was my idea, and the idea of a lot of other people too, it seems. But this documentary indicated that we were all wrong. Ardi walked upright in a forest setting, where there aren't long convenient sightlines anyway so the advantages of bipedalism aren't at all as obvious.

Another challenge: I have long believed that the opposable thumb was crucial to the separation of hominids from other primates. Our thumb makes us tool-users, which in turn presumably spurred the expansion of the brain, the development of complicated social groups, and so forth. Right? Well, maybe in some later era the opposable thunb played the sort of important causative role that has been attributed to it. But bipedalism and other changes underway in Ardi's day would have preceded all that. Her thumb looks distinctly unimpressive.