Jet Black said:
our common ancestor would have been genetically inbetween but morphologically far more similar to a chimp. See our common ancestor with the chimp came from the same environment as the chimp, but what-became-the chimps (more or les morphologically staying the same) stayed in the forest and didn't change much, whereas we ventured out on to the savannah, for whatever reasons (predominantly because the forests were receding at the time and so there wouldn't have been enough room in the forests for all the common ancestors)
So you're saying the common ancestor would have looked more like a chimp, and that some chimps evolved; some didn't.
The Aquatic Ape Theory (AAT) offers an alternative scenario. It suggests that when our ancestors moved onto the savannah they were already different from the apes; that nakedness, bipedalism, and other modifications had begun to evolve much earlier, when the ape and human lines first diverged.
From:
http://www.primitivism.com/aquatic-ape.htm
I see NO reason for the change in some and not in others. Environment is ruled out as a factor if you say what the above article says (they changed while still in the forest with the other monkeys). Nourishment, etc., would have been the same. So what caused the divergence?
Even if we did change AFTER venturing out, consider the following:
chimps don't swim, so a life-aquatic would probably be ruled out if the common ancestor was really physically that similar to a chimp
i doubt a chimp could out run a lion, or similar large predator, so a desert dwelling (or somewhere in the plains) would be doubtful, since they would have few (if any) trees to hide in, depending... and their size alone is enough to get them eaten out there.
i would assume if they went for a colder climate in the mountains, we would be looking more like Sasquatch due to temperatures... but what would they eat up there?
Yes, I see them drowning, boiling, freezing, or being digested... sorry I'm so skeptical

can't help it.