Sure, but our various brain centers are often dedicated to a particular kind of thinking. It might be quite a stretch for the climbing center to be re-purposed for another activity. Nonetheless, this happens in children who suffer brain damage. Their brains are still growing so the environment plays a large part in the development of new synapses. "Allowing" indeed. After a few million years of bipedal living, our distant ancestors began inventing tools. Archeology tells us that the flint blade was the first tool made of a material that would last long enough for us to find it. And the flint blade started us down a much different evolutionary path. Those ancestors used their blades to scrape the leftover meat from carcasses abandoned by predators, who could not get to it. This increased the protein content of our meals, which made it possible for someone with a slightly larger brain to survive, since the brain uses most of our protein intake. Eventually the big-brain mutation led to a new species with a higher IQ. That species figured out how to attach flint blades to wooden handles, allowing them to hunt, and making the transition from scavenger to predator. Ultimately we ended up with a forebrain about three times as big as the chimpanzee, our closest relative, and our hunting methods became very sophisticated... or not, since chasing animals into a cul de sac or off a cliff was a popular hunting technique. Before long we lost the huge gut hosting the bacteria culture necessary to digest raw plant tissue, and became obligate carnivores. The only reason people can now survive without animal protein is that a couple of million years ago one of our ancestral species tamed fire; cooking plant tissue makes the protein easier to extract. As was suggested earlier, bipedalism comes with automatic advantages, such as being able to carry food and babies. It was certainly bipedalism that set us on the track to becoming the apex predator of the entire planet: we eat the flesh of both bears and sharks. Having hands free allowed us to become inventors. One of the things we invented was sign language, although that was eventually supplanted by vocal communication (probably in the Paleolithic Era around 70KYA when we find an explosion of complex coordinated activities that could not possibly have been performed by people who were using their hands to speak) and eventually writing (this technology left its own "fossils" and we can date it to the early Bronze Age around 5 KYA). The anatomy of Ardipithecus, the transitional species, indicates that she was an efficient and stable walker. There's no reason why the prehensile hallux that allowed quick retreat into the trees would have been a detriment to walking. There are no tool fossils with Ardi. But that doesn't mean they couldn't have used sticks and other material that doesn't fossilize. Chimpanzees use sticks as tools, and other species of mammals, birds and even arthropods use various natural objects as tools. Many primates are highly social so there's no reason to assume that Ardi's ancestors, much less Ardi herself, were not. Of the six modern species of Great Apes, only the orangutan prefers a solitary life. In general, warm-blooded animals that become aquatic have such an advantage over the gill-breathers that they evolve a larger size to discourage predation and become (at least one of) the dominant species. The cetaceans are the descendants of primitive hippopotamuses who swam all the way to the end of the river, liked what they found there, and stayed. Seals are caniforms, closely related to dogs, raccoons, bears, weasels and skunks. If our ancestors were aquatic, what made them change their minds and go back to a much more difficult life on the land? (The first animals to crawl out of the sea and colonize the land had no competition.) We have plenty of fossils of our own ancestral species. Surely they can compare this print to a foot from the same timeline. It looks rather modern, but our ancestors have been walking bipedally for several million years, making it likely that the shape of the foot was perfected long ago.