Evolution isn't just an idea that sounds good to biologists. It is good science because it makes predictions about what we should expect to find in our world. Evolution says that if members of the same species become separated for a period of time, they may take different trajectories in their evolutionary development, depending on the environment. Here's an interesting photo that I believe is of a member of an isolated tribe called the Korowai. Go here for other amazing photos of them.
This photo is from a youtube clip, which explains why it is grainy.