The probability of play, depending on the focal subject’s sex and on kin category, in rhesus macaques from 2004 to 2008 on Cayo Santiago, Puerto Rico. Boxes represent the first to third quartile of observed values, solid lines show the median, dashed lines show the values fitted by the model, and each circle represents a data point for a focal subject. (a) Comparison over all three kin categories. (b) Detail showing only comparison between paternal kin and nonkin.