Two million years ago somewhere in Africa, a small group of individuals became separated from other australopithecines. This population bottleneck led to a series of sudden, interrelated changes-in body size, brain size, skeletal proportions, and behavior-that jump-started the evolution of our species. 'Evolution' is the change of the characteristics of an organism over time. All life on Earth is descended from its own ancestor around 4 billion years ago. It was studied in the mid-19th century by Charles Darwin. Often mused about by Sheldon. The Big Bang Theory Wiki is a FANDOM TV Community.