Supplementary Material for: Anchoring the Clade: Primate-Wide Comparative Analysis Supports the Relationship between Juvenile Interest in Infants and Adult Patterns of Infant Care

Female-biased juvenile interest in infants is common in primates. Proposed hypotheses to explain juvenile infant interest are that it helps immature individuals learn to parent, is a by-product of selection on adult infant care behavior, is kin-selected cooperative rearing, or is a form of harassment. If juvenile infant interest is associated with adult infant care, either functionally or as a by-product, sex-biased patterns of juvenile infant interest and adult infant care should show correlated evolution; if juvenile infant interest functions as cooperative rearing or harassment, they should not. Comparisons of nested bayesian Markov chain Monte Carlo models of independent and dependent evolution of juvenile infant interest and adult infant care indicate strong support for coevolution of juvenile infant interest and adult infant care. Expanding comparative analysis to include available data from lemurs strengthens this support, suggesting that the function of juvenile infant interest does not differ between strepsirrhines and haplorhines. As such, strepsirrhine taxa currently maintained in captivity will be particularly useful in future work aiming to test between the learning to parent and by-product hypotheses for juvenile infant interest.