Scientists have long envisioned the human "family tree" as a straight-line progression from the apelike australopithecines to the enigmatic Homo habilis to the famous Neanderthals, culminating in us, Homo sapiens . But this model is unlike the evolutionary patterns known for all other vertebrates--patterns that typically reveal multiple branchings and extinctions. In Extinct Humans , Ian Tattersall and Jeffrey Schwartz present convincing evidence...