The book Sapiens: A Brief History of Humankind[1] is relevant here (which I've been reading and thoroughly enjoying recently) if anyone wanted to seek out some longer-form information on this and the topics around human evolution and development. The semantics here are really interesting to me because the book immediately points out that not too long ago there were at least 6 species of human on earth at the same time (going by homo=humans, sapiens is what distinguishes us). That concept had never been so explicitly stated to me before, and I find it really fascinating to unpeel.

[1] http://smile.amazon.com/gp/product/0062316095/ref=s9_simh_gw...