Fig. 2.

Facial resemblance between relatives in 4 primate species, according to human judges. The y-axis shows the proportion of facial recognition divided by the rate expected by chance. The dashed line represents the recognition rate expected by chance. Facial kin detection rates significantly exceeded the rate expected by chance in chimpanzees, gorillas, and mandrills (exact binomial tests: p < 0.001). In contrast, human judges are not able to detect kin visually in baboons (exact binomial tests: p = 0.63). Error bars represent the standard error of the weighted means. The rate of recognition was not different among chimpanzees, gorillas, and mandrills but baboon scores were significantly different from those of the other species. See text for details. (**p < 0.01; non significant (n.s.) p > 0.05).