[AppyPappy]

Are they saying that man and neanderthal could not produce offspring?

[WilliamWallace1999]

Not the case at all, just that it did not happen with enough regularity to show up on the human mtDNA pool. Mitochondrial DNA is only inherited from the mother and provides a genetic timeline for the divergence of cultures.

Horses and donkeys can breed, but they produce sterile offspring. Other interspecies breeding has also been documented.