As apes evolved into humans, there were many lines that interbred to become modern humans...
Where did the others go? It's pretty clear that, in Europe, at least....we interbred with Neanderthals. Anyone who's had DNA tested is likely to have Neanderthal genes. They weren't the hulking, stupid brutes they've been alleged to be--they were artistic, tecnologically capable and certainly cared for their families. Neanderthals got a bad rap!
Now--if we'd only branched out from bonobos instead of chimpanzees......