[qam1]

You are right, Darwin does not outright say that we killed off the Neanderthals in war, reducing the humanoid genetics pool from two species down to one. But one thing very strange about humanoids as compared to say the variety of fish, is why there is only ONE humanoid species still alive? This is very odd. Obviously there is enough food in the world for many similar species to survive. The only explanation that makes sense is we killed them off in anger or competition. This fits with Darwin's ideas in the Descent of Man.

Then explain why there's more than one species of Ants?

To quote E.O. Wilson

"Human generals might do well to study ants, arguably the most warlike and aggressive creatures on the planet. Ant colonies ambush, kidnap, rob, and raid other ants. There are even "suicide bomber" ants that explode their own bodies in order to spray enemies with toxic secretions. If ants had nuclear weapons, they would probably end the world in a week."

[Reeses]

Then explain why there's more than one species of Ants?

It seems possible that if given enough time some type of ant would eventually take over the world, and kill off all resource competitors. They may still get their turn. A war making disposition leads to developing intelligence far in excess of that needed to find food and shelter. Insects never get very big compared to other animals for some reason which may be the reason their brain size and cognitive function seems to have hit a biological road block. But that could change.