title: Sex differences in wild chimpanzee behavior emerge during infancy.
abstract: The role of biological and social influences on sex differences in human child development is a persistent topic of discussion and debate. Given their many similarities to humans, chimpanzees are an important study species for understanding the biological and evolutionary roots of sex differences in human development. In this study, we present the most detailed analyses of wild chimpanzee infant development to date, encompassing data from 40 infants from the long-term study of chimpanzees at Gombe National Park, Tanzania. Our goal was to characterize age-related changes, from birth to five years of age, in the percent of observation time spent performing behaviors that represent important benchmarks in nutritional, motor, and social development, and to determine whether and in which behaviors sex differences occur. Sex differences were found for indicators of social behavior, motor development and spatial independence with males being more physically precocious and peaking in play earlier than females. These results demonstrate early sex differentiation that may reflect adult reproductive strategies. Our findings also resemble those found in humans, which suggests that biologically-based sex differences may have been present in the common ancestor and operated independently from the influences of modern sex-biased parental behavior and gender socialization.
authors.affiliation: Department of Psychology and Biological Foundations of Behavior Program, Franklin & Marshall College, Lancaster, Pennsylvania, United States of America; Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America.
authors.forename: Elizabeth V
authors.initials: EV
authors.lastname: Lonsdorf
authors.affiliation: Center for the Advanced Study of Hominid Paleobiology, The George Washington University, Washington, DC, United States of America.
authors.forename: A Catherine
authors.initials: AC
authors.lastname: Markham
authors.affiliation: Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America; Committee on Evolutionary Biology, University of Chicago, Chicago, Illinois, United States of America.
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Heintz
authors.affiliation: Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, Illinois, United States of America.
authors.forename: Karen E
authors.initials: KE
authors.lastname: Anderson
authors.affiliation: Department of Government, Franklin & Marshall College, Lancaster, Pennsylvania, United States of America.
authors.forename: David J
authors.initials: DJ
authors.lastname: Ciuk
authors.affiliation: The Jane Goodall Institute, Vienna, Virginia, United States of America.
authors.forename: Jane
authors.initials: J
authors.lastname: Goodall
authors.affiliation: Center for the Advanced Study of Hominid Paleobiology, The George Washington University, Washington, DC, United States of America.
authors.forename: Carson M
authors.initials: CM
authors.lastname: Murray
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D001522:Behavior, Animal; D005260:Female; D008297:Male; D009043:Motor Activity; D002679:Pan troglodytes / Q000254:growth & development* / Q000502:physiology; D012098:Reproduction; D012727:Sex Characteristics; D012919:Social Behavior; D013037:Spatial Behavior; D013636:Tanzania