Humans have a complex emotional relationship with the other members of our great apes family. Great apes are appealing because of the close resemblances we share, but these resemblances can cause feelings of aversion and disgust. We propose that these feelings may stem from the uncanny valley – the point at which someone or something becomes almost, but not quite human. We argue that the uncanny valley has made great apes an effective tool for a particular type of dehumanization, known as simianization. Simianization has been especially prolonged and pervasive towards black people, dating from the transatlantic slave trade and continuing today. In the reverse direction, the humanness of great apes has made them a source of fascination, but has not saved them from extensive population decline and may have facilitated their exploitation. Preliminary research into decreasing the human-animal divide shows promise for mitigating the negative impact of simianization of people and for improving attitudes towards, and the welfare of, great apes.