Primate Kinship: Contributions from Cayo Santiago

Research on Cayo Santiago and Japan deserves credit for launching the study of primate kinship and for continuing to help shape it in important ways. This review describes the origins of kinship research on Cayo Santiago, beginning with Donald Sade's pioneering work establishing the concepts of kin preferences, matrilineal dominance systems and incest avoidance. It then reviews subsequent research by later Cayo Santiago researchers and alumni, focusing primarily on maternal kinship. Together these researchers have greatly expanded our knowledge of kin preferences in rhesus in terms of (i) what age-sex classes, behaviors and types of kin show them, (ii) the ways in which kinship interfaces with rank, sex, age, and dispersal patterns, and (iii) the graded and variably limited nature of kin preferences in terms of degree of relatedness. Second, the argument for kin selection at least for some types of behavior has survived challenges posed by several alternative explanations, and has been both strengthened by recent findings of paternal kin preferences and narrowed by studies showing that unilateral altruism may extend only to very close kin. Third, work on Cayo Santiago has contributed to an appreciation that both current conditions and inherent social characteristics may influence the strength of kin preferences, and fourth, it has contributed to an understanding of the possible origins of our own species' family systems. Cayo Santiago became a leader in kinship research in large part because of management practices that produce known extended lineages. These lineages have promoted and accelerated research on kinship, prompting other researchers to investigate its importance in other groups and species, where its effects only then became clear. The extended lineages remain valuable tools for research on a species that lives in a broad range of environments in the wild, including those with key parallels to Cayo Santiago.