research :: kin recognition
We have been interested in understanding whether nonhuman primates are able to detect kin relationships by studying the faces of related and unrelated individuals. In 1999, Parr and de Waal published a study in chimpanzees describing better recognition of the faces of unfamiliar mothers paired with sons compared to mothers paired with daughters. This advantage for recognizing similarities in male faces might serve as an inbreeding avoidance mechanism in this female-dispersal species, such that females should avoid mating with any male who resembles their mother.
However, the above result may also be explained by male-distinctiveness. Male faces are more distinctive and easier to recognize than female faces, thus the results may simply be biased by attention to male faces. We are now expanding on these findings to address visual kin recognition processes in chimpanzees and rhesus monkeys using faces of both mothers and offspring and fathers and offspring (see Figure below). This allows for an important comparison of the two main hypotheses, inbreeding avoidance or male-distinctiveness.
Our studies replicated the mother-son advantage in chimpanzees (in one of two studies), but failed to find any evidence of this in rhesus monkeys. Instead, rhesus monkeys showed excellent performance matching the faces of males compared to females. This include fathers and offspring, any parent and sons, and the best performance was between photographs of fathers and sons.
Researchers believe that among mammals, male-dispersal (moving away from the natal group) is the primary means for avoiding inbreeding as it reduces the relatedness between males and females within the group. Because rhesus monkeys show male-migration, they may not need an additional visually-based kin recognition mechanism to reduce inbreeding. Chimpanzees, however, show varied patterns of gender-based dispersal, but primarily females-disperse. In these instances, females would be greatly aided by a visually-based mechanism to avoid mating with related extra-group males. Our data support these basic assumptions.
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Figure. Faces of related chimpanzees and rhesus monkeys. MD = mothers and daughters; MS = mothers and sons; PD = fathers and daughters; PS = fathers and sons. Parent is the left image of the pair.
