the book "Life on Earth The Story of Evolution" by Steve Jenkins is a good book. It might be to elementary for your son, I don't know but it's worth a check out at the library. He starts with the beginning of life, moves on to Darwin and illustrates how beak shaped diverged, then survival of the fittest, variation and mutation, how new species develop, good designs and extinctions.
THis book doesn't have anything about skin color. I do have a book that has that in it but I'll have to think about which book and get back to you.
