We probably infected European Neanderthals with our African diseases

Neanderthal populations of Europe and Asia were probably weakened by pathogens that we homo sapiens emigrants brought with us when we moved away from our African birthplace. We probably didn't actually kill them in an outright manner, but the Neanderthals would have surely picked up our diseases such as tapeworms, tuberculosis, stomach ulcers and herpes. And these new afflictions would have no doubt sickened members of the old community to such an extent that they could no longer care for themselves by foraging and hunting.

Neanderthals seem to have been driven to extinction around 40,000 years ago. We didn't necessarily act deliberately in killing them. It has been suggested that we Humans and certain Neanderthal friends even got around to friendly sessions of rock-and-roll, resulting in genetic traces that remain in our present chromosomes. But the Neanderthals nevertheless disappeared from Europe and Asia soon after our arrival. You might say that it wasn't really our fault. But in a sense, it was.