Hybrids - the children that result from the mating of closely-related species - usually fail. For example if you cross a donkey and a horse you get a mule, but mules are born sterile. Being born weak or sterile is useless if evolution depends on survival of the fittest...

But now some researchers, after pottering around with sunflowers for 15 years, have shown that:

"the sudden mixing and matching of different species' genes can create genetic super-combinations that are considerably more advantageous to the survival and reproduction of their owners than the gene combinations their parents possess."

It's not hybrids breeding with each other, its hybrids breeding with the species of one of the parents.

The implication is that early human species may have interbred to create us, the super hominids.