Debra Lieberman: U of Hawaii Psychology

Mechanisms for detecting kin rely on cues that correlated with relatedness in ancestral environments to adaptively regulate mate selection and altruistic effort. For siblings, one potential cue, proposed by Edward Westermarck, is co-residence duration. Another cue that would have been highly predictive of siblingship is seeing one’s mother caring for a newborn. Data from a series of investigations show that these two cues regulate the development of altruistic motivations, sexual aversions, and, as a by-product, moral sentiments relating to incest. Revisiting the natural experiments that fueled the discussion over how sexual aversions and moral sentiments develop, I show that these two cues also explain the data from the Taiwanese minor marriages. Furthermore, I provide new evidence that childhood co-residence predicts altruistic tendencies, sexual aversions, and moral sentiments in individuals raised in the communal fashion of the Israeli Kibbutzim.