While the purpose of Mori's  paper[, The Buddha in the Robot: A Robot Engineer's Thoughts on Science and Religion,] was to inform robot design, in a concluding paragraph he cannot resist offering his own theory about the origins of the uncanny valley. He writes: "When we die, we fall into the trough of the uncanny valley. Our body becomes cold, our color changes, and movement ceases." Human models fall into the uncanny valley because they remind us of death. "It may be important to our self-preservation," he concludes. […]
But all along Mori hasn't seen our avoidance of death as a consequence of repressed emotions the way Freud did. Instead he has understood it to be a mechanism we developed to keep ourselves safe. Nearly every hypothesis since has had this flavor. It has been suggested, for instance, that we avoid almost human figures because their peculiarities make them look sick, and we have developed an evolutionary mechanism for steering clear of pathogens. Another theory posits that we avoid figures with features slightly off from our own because they appear to be less-than-ideal mating material.
Ghazanfar rejects all of these hypotheses. "What is really going on is much simpler," he says. He believes the uncanny valley response occurs because an animal--human or nonhuman--is evolutionarily inclined to develop an expectation of what members of its species should look like, a supremely important skill, as it lets the animal know with whom it can and cannot interact.