Did the Common Marmoset Self-Domesticate?

Abstract

Domesticated animals share a distinctive set of traits not observed in their wild ancestors. Referred to as the “domestication syndrome” (DS), these traits are considered the byproduct of selection against aggression. Accordingly, wild animals that show low levels of aggression and a range of correlated phenotypic differences have been hypothesized to have self-domesticated (the self-domestication hypothesis). The common marmoset, a cooperatively breeding primate, should be a candidate species for having experienced this “self-domestication” process as they exhibit white forehead patches—a distinct marker of the DS—and readily engage in cooperative vocal exchanges, a prosocial behavior related to cooperative breeding. Here, we investigated the self-domestication of the marmoset by establishing whether the white patch aligns with the DS or scales with body size. Using image analysis, we found that white patch size varied between marmosets and could not be fully explained by body size. The presence of the DS in the marmoset allowed us to then test a recently proposed theory for its origin, which has remained a mystery for more than 140 years. The neural crest cell hypothesis proposes that the DS results from mild neural crest cell deficits during embryonic development, indicating that traits of domestication should be correlated. We compared white patch size to vocal behavior and found evidence in support of this hypothesis. These findings show that marmosets have self-domesticated and provide some of the first evidence for an explanation of the mechanism behind the DS.

Keywords: domestication syndrome; self-domestication; cooperative breeding; vocal exchange; neural crest cells