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Existing data on bonobo and chimpanzee dental eruption timing are derived predominantly from captive individuals or deceased wild individuals. However, recent advances in noninvasive photographic monitoring of living, wild apes have enabled researchers to characterize dental eruption in relatively healthy individuals under naturalistic conditions. At present, such data are available for only one population of wild chimpanzees. We report data for an additional population of wild chimpanzees and the first dental eruption data for wild bonobos.

We collected photographs and video footage of teeth from the open mouths of wild bonobos and East African chimpanzees of known age from LuiKotale, Democratic Republic of the Congo, and Gombe National Park, Tanzania, respectively. We scored the presence and absence of deciduous teeth from photographs and video footage to characterize deciduous dental eruption timing in these two populations.

Deciduous dental eruption ages in our sample fall within the range of variation previously documented for captive chimpanzees, but eruption ages are later in wild than in captive contexts. We found substantial variation in deciduous canine eruption timing, particularly among bonobos. One bonobo had a deciduous canine present by 227 days old while another did not have a deciduous canine present at 477 days old.

Our data indicate that deciduous teeth erupt later in wild individuals than in captive individuals. We also found that deciduous dental eruption timing varies considerably between individuals within our study populations, a pattern that is consistent with previous studies. Future studies should consider sources of variation in deciduous canine eruption timing and relationships with other aspects of life history as additional data become available.

The prolonged juvenile period exhibited by primates is an evolutionary conundrum. Here we examine wild chimpanzee feeding development in the context of two hypotheses regarding prolonged development in primates: the needing‐to‐learn hypothesis and the expensive brain hypothesis.

We studied wild chimpanzee (Pan troglodytes schweinfurthii) offspring at Gombe National Park, Tanzania. We analyzed 41 years of observational behavioral data collected between 1975 and 2016 from 81 offspring. We characterized feeding development in the first 10 years of life via four different measures: (1) proportion of observation time spent feeding; (2) diet composition; (3) diet breadth; and (4) diet maturity as measured by similarity to maternal diet. We used mixed effects models to examine changes with age and by sex, while controlling for season.

Feeding time, diet breadth, and diet maturity exhibited the most substantial increases with age in the first 6 years, with no significant change thereafter. Males and females showed different patterns of change in diet breadth by age, but did not differ by age 10. Diet composition did not change significantly with age and did not differ by sex.

We found that chimpanzee offspring attained adult‐like feeding behaviors between 4 and 6 years of age, concomitant with the completion of weaning. Thus, our data do not support the needing‐to‐learn feeding skills hypothesis of a prolonged juvenile period, but additional data are needed to evaluate how and when adolescent chimpanzees are able to make foraging decisions independent of their mothers. Existing data on growth provides support for the expensive brain hypothesis, however, these hypotheses are not necessarily mutually exclusive. As more studies across taxa accumulate sufficient datasets on a range of developmental metrics, we will be able to achieve a more robust understanding of prolonged development in primates.

A key feature of human life history evolution is that modern humans wean their infants 2–4 years earlier on average than African apes. However, our understanding of weaning variation in apes remains limited. Here we provide the first such report in chimpanzees by examining weaned age variation using long‐term data from Gombe National Park, Tanzania.

We analyzed 41 years of observational behavioral data from 65 offspring of 29 mothers to examine the relationships between weaned age (defined as cessation of suckling) in wild chimpanzees and maternal age, dominance rank and parity, and offspring sex. We used Cox proportional hazards regression with mixed effects to model time to weaning and to examine potential sources of variation in offspring weaned age.

We found that male offspring were less likely than female offspring to wean by a given age and that weaned age of males varied more than weaned age of females. In addition, maternal dominance rank interacted with offspring age, such that low‐ranking mothers were less likely to wean offspring early, but this effect decreased with offspring age.

We found that male offspring and offspring of low‐ranking females were less likely to wean early, but did not find evidence for variable weaning according to maternal age or parity. As more data accumulate, we will be better able to disentangle the effects of maternal dominance rank, age and parity. Such studies will not only provide a richer understanding of living ape life history characteristics, but will also provide an important framework for understanding the evolution of early weaning in humans.