Results are presented of multivariate quantitative analyses of the relationships among 19 demographic, ecological, and social variables observed in 29 populations representing 21 primate species. The variables are group size, population density, day range, home range, percentages of adult males, adult females, and juveniles, body weights of adult males and females, sex ratio, arboreality, biomass, available food, frequencies of aggression, social grooming, play, and copulation. Analysis shows that three social behavior variables (frequencies of aggression, play, and copulation) are predicted significantly by using data on group size, density, day range, home range, and arboreality as predictors. Principal components analysis allows construction of a model that places the 29 populations in four clusters that compare closely with the adaptive grades of Crook and Gartlan (1966). The high incidence of infants in populations of large terrestrial primates probably results from slow maturation rather than from operation of r and K selection.