For years, anthropologists suspected that Homo sapiens cross-bred with Neanderthals before our closest ancestor went extinct.
via Top Scientific Discoveries of 2011 | Wired Science | Wired.com.
One story I got from the Open-source Intelligence side of things was that Humans mated with the Neanderthals, and one of the genetic outcomes was a super-large brain. My assumption at the time was that these mutated-Neanderthals killed off the guys pictured here.
As this story may suggest, they probably killed off the other Humans as well, ha!
The Image 