Are ethnic groups biological "species" to the human brain? Essentialism in our cognition of some social categories

If ethnic actors represent ethnic groups as essentialized "natural" groups despite the fact that ethnic essences do not exist, we must understand why. This article presents a hypothesis and evidence that humans process ethnic groups (and a few other related social categories) as if they were "species" because their surface similarities to species make them inputs to the "living-kinds" mental module that initially evolved to process species-level categories. The main similarities responsible are (I) category-based endogamy and (2) descent-based membership. Evolution encouraged this because processing ethnic groups as species-at least in the ancestral environment-solved adaptive problems having to do with interactional discriminations and behavioral prediction. Coethnics (like conspecifics) share many strongly intercorrelated "properties" that are not obvious on first inspection. Since interaction with out-group members is costly because of coordination failure due to different norms between ethnic groups, thinking of ethnic groups as species adaptively promotes interactional discriminations towards the in-group (including endogamy). It also promotes inductive generalizations, which allow acquisition of reliable knowledge for behavioral prediction without too much costly interaction with out-group members. The relevant cognitive-science literature is reviewed, and cognitive field-experiment and ethnographic evidence from Mongolia is advanced to support the hypothesis.