![]() In terms of physical growth, a long-term analysis of weight data from Gombe, Tanzania, showed that female chimpanzees are slightly lighter than males up to age 10, when adult dimorphic patterns begin to emerge and eventually result in a male/female body mass ratio of 1.25. Only after the age of 10 years do most chimpanzees start to spend the majority of time away from their mother, although it is not uncommon for adult chimpanzees (those over 12) to spend a significant amount of time with their mothers. continually traveling and socializing with) through the juvenile years, until at least the age of 8. Offspring are nutritionally dependent on their mother through infancy until weaning between the ages of 3 to 5, but remain behaviorally dependent (i.e. Physical contact with the mother characterizes most of the first two years of life. Previous research has described the general pattern of wild chimpanzee development. Male chimpanzees also participate in more direct physical aggression than females, both within communities during competition for dominance status and between communities during cooperative territorial defense. As such, male-male dyads have stronger association indices than female-female dyads. In East African chimpanzees ( Pan troglodytes schweinfurthii), there are distinct sex differences in sociality, such that adult females are significantly less gregarious than adult males, spending much of their time accompanied only by their dependent offspring (Gombe:, Kanyawara:, Mahale: ). Additional sex differences in foraging include a female-bias towards gathering insects via tool use, and a male-bias towards hunting of vertebrate prey. These include differences in feeding and ranging patterns, such that females typically range and feed in small overlapping core areas while males range more broadly throughout the territory. Within these communities, adult male and female chimpanzees show distinct sex differences in behavior. Wild chimpanzee communities are multi-male, multi-female and are characterized by a male dominance hierarchy in which philopatric males form the stable core of the community and defend a group territory. Moreover, the mother-infant relationship is of exceptional importance for developing chimpanzees given the lengthy period of dependence and lack of overt paternal care (, but see ). Chimpanzees also share behavioral and developmental characteristics with humans, including a fission-fusion social system, , and a relatively long period of nutritional and social dependency. Chimpanzees and humans have many genetic similarities as well as similarities in physiology and growth. ![]() 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. A persistent topic of discussion and debate is the relative contribution of biological versus social influences to such differences (reviewed in ) including how they may be driven by differential treatment by parents and teachers. Sex differences in behavior and developmental trajectories in human children are of great interest to researchers in a variety of fields of study. ![]() 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. These results demonstrate early sex differentiation that may reflect adult reproductive strategies. 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. ![]() 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. 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. 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. The role of biological and social influences on sex differences in human child development is a persistent topic of discussion and debate.
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