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.
Highlights
Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields of study
Hereafter, when referring to patterns at particular ages, we will use the age at the start of the block to refer to a six month time period (e.g. ‘age 29 refers to the six month time block from age 2 to 2.5 years)
Suckling and Eating Suckling did not show a significant change with age or sex, with mean percent of time observed suckling ranging from 2–3.71%
Summary
Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields of study. A persistent topic of discussion and debate is the relative contribution of biological versus social influences to such differences (reviewed in [1]) including how they may be driven by differential treatment by parents and teachers [2]. Given the potential effect of cultural and social influences on child development, non-human primates, and chimpanzees (Pan troglodytes ssp.) in particular, are an important study species for understanding the biological and evolutionary roots of sex differences in human development. Chimpanzees share behavioral and developmental characteristics with humans, including a fission-fusion social system [5,6,7] and a relatively long period of nutritional and social dependency [8]. The motherinfant relationship is of exceptional importance for developing chimpanzees given the lengthy period of dependence and lack of overt paternal care ([9], but see [10])
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