Due to the intense selection pressure against inbreeding, humans are expected to possess psychological adaptations that regulate mate choice and avoid inbreeding. From a gene’s-eye perspective, there is little difference in the evolutionary costs between situations where an individual him/herself is participating in inbreeding and inbreeding among other close relatives. The difference is merely quantitative, as fitness can be compromised via both routes. The question is whether humans are sensitive to the direct as well as indirect costs of inbreeding. Using (...) responses from a large population-based sample (27,364 responses from 2,353 participants), we found that human motivations to avoid inbreeding closely track the theoretical costs of inbreeding as predicted by inclusive-fitness theory. Participants were asked to select in a forced choice paradigm, which of two acts of inbreeding with actual family members they would want to avoid most. We found that the estimated fitness costs explained 83.6% of participant choices. Importantly, fitness costs explained choices also when the self was not involved. We conclude that humans intuit the indirect fitness costs of mating decisions made by close family members and that psychological inbreeding avoidance mechanisms extend beyond self-regulation. (shrink)

Discerning adaptations from by-products is a defining feature of evolutionary science. Mehr, Krasnow, Bryant, and Hagen posit that music is an adaptation that evolved to function as a credible signal. We counter this claim, as we are not convinced they have dispelled the possibility that music is an elaboration of extant features of language.

To understand the consequences of cleansing, Lee and Schwarz favor a grounded procedures perspective over recently developed disgust theory. We believe that this position stems from three errors: (1) interpreting cleansing effects as broader than they are; (2) not detailing the proximate mechanisms underlying disgust; and (3) not detailing adaptive function versus system byproducts when developing the grounded procedures perspective.

Fitouchi et al. persuasively argue against popular disgust-based accounts of puritanical morality. However, they do not consider alternative account of moral condemnation that is also based on the psychology of disgust. We argue that these other disgust-based accounts are more promising than those dismissed in the target article.