By Ian Tattersall and Jeffrey Schwartz
REVIEWED ON FEBRUARY 15, 2003
Early on anthropologists envisioned the human "family tree" as a straight-line progression from the bipedal apes to Homo habilis to Homo erectus to the Neanderthals culminating in us, Homo sapiens. The problem was that this model was unlike the evolutionary pattern of any other known vertebrate (or any organism for that matter) which revealed multiple branching and extinctions.
It wasn't long before a number of South African fossils were discovered that demonstrated two species of these early bipedal apes existed at the same time, one of which was a specialized vegetarian that went extinct, leaving no successors. Then it became increasingly apparent that the Neanderthals were not a direct ancestor to modern humans but were in fact a side branch whose extirpation was at least partially at the hands of our direct modern human ancestors who invaded Europe 40,000 years ago.
Extinct Humans presents convincing evidence that over 15 different species of humans have existed over time, and that during the period of 3 to 1 million years ago upwards of 10 different species of humans existed simultaneously.
How did they differ from us? What did they look like? Which are direct ancestors to us and which went extinct leaving no successors? And probably most curious of all, why now is there only a single human species?