We are domesticated animals

[bhikkhu]

11. Twenty-two species, by current estimates

Probably we didn't kill them all off, but given the inbred intolerance that is so common, and so difficult to teach out of children even in these highly civilized times, its not hard to imagine that we had a lot to do with most of it.

Good reading on the topic: http://www.amazon.com/The-Last-Human-Twenty-Two-Species/dp/0300100477