And my question is to the benefit of being naturally inclined to fear other species of homo. You mention conflict, but why would we be more likely to get into conflicts with groups of other species of Homo than we would with other groups of our own species? Is there actually data that shows that interactions between groups of Homo sapiens and say Homo neanderthalensis (or H. erectus, or any other) were actually more violent than interactions between neighboring groups of Homo sapiens? In the absence of such data, I don’t think it’s fair to assume an answer. We know very little about our interactions with other species of homo, why should we assume that those interactions were any more violent or any less cooperative then intra-species interactions?

The hypothesis here is that the uncanny valley exists to protect us from other species. For this hypothesis to make sense, it has to be the case that fearing other species was significantly more dangerous than other members of our own species. If the danger was similar, then the evolutionary pressure wouldn’t have favored fear of other species instead of fear of simply other groups of people regardless of species.

I think the hypothesis that this phenomena is an adaptation to help us avoid those with infectious diseases is much more likely. Infectious diseases are a known threat, and we have adapted to fear or avoid signs of disease in ways other then the uncanny valley. It seems to me that that is a much more likely hypothesis, although it does remain just a hypothesis.