Search for: All records

Adolescence is generally considered the life stage with peak risk-taking among humans, though this may be specific to the type of risk. To circumvent the safety constraints that limit experiments of physical risk-taking in humans, we used the natural behavior of wild chimpanzees as a model. All chimpanzees must navigate the same arboreal substrates where falls from the tree canopy are a major cause of trauma, and therefore have clear fitness consequences. Using instances of locomotor free flight as a proxy, we found that height from the ground and sex did not predict physical risk-taking. The latter finding is similar to human and chimpanzee economic risk-taking studies. We found that physical risk-taking correlated with age, peaking in infancy and decreasing gradually thereafter through juvenility and adolescence. We hypothesize that a similar pattern would be exhibited in humans if oversight were relaxed earlier in childhood, as it is among chimpanzees.Not Available 

ABSTRACT ObjectivesDistinctive aspects of great ape anatomy and positional behavior, including upright torso stability and suspension, are hypothesized to have evolved to facilitate ripe fruit‐eating in the terminal zone of tree canopies at large body size. Fossil discoveries challenge this view, and we test this perspective by investigating relationships among feeding posture, food type, and canopy zone in chimpanzees. Materials and MethodsFocal follow data were collected over 10 months on 103 chimpanzees from Ngogo, Kibale Forest, Uganda. Generalized Linear Mixed Modeling was used to examine the effects of food, canopy location, and age on arboreal feeding posture versatility. Branch size and number, and tree size and species were also examined. ResultsWhen considering all trees, consuming young leaves versus ripe fruit positively affected versatility. When examining only large‐canopy trees, eating leaves versus ripe fruit had no effect, but unripe versus ripe fruit had a negative effect. Terminal zone feeding was associated with an increase in versatility, and in this zone, consuming leaves versus ripe fruit had a negative effect. Versatility was inversely correlated with age, varied across tree species, and was higher on small branches and in small trees. DiscussionA positive “terminal zone effect” on versatility was detected in large trees, with behavioral impact varying by food type. Within the forest as a whole, consuming leaves over ripe fruit increased versatility. Thus, food type and availability may, in different combinations, lead to equifinality in great ape positional versatility. Hominoid morphofunctional specializations could thus evolve in many ecological contexts. 

Investigations into the role of selection in the origin of human bipedalism using ape models have relied heavily on behavioral frequency data. However, analysis of video of wild apes has the advantage of capturing the details of the entirety of each rare, brief bipedal bout witnessed, not just the moment detected in observational studies. We used video to explore the behavioral context and effects of several variables on bipedalism across all ages in wild forest-dwelling chimpanzees from Ngogo, Uganda. We found, as in earlier studies, that adult chimpanzees used bipedalism in the context of foraging; however, unlike earlier studies, we found that while foraging was the predominant behavioral context during arboreal bipedalism, terrestrial bipedalism was more varied in contextual composition. We also found that these different behavioral contexts of bipedalism were associated with different variables. Specifically, foraging was associated with arboreality, hand assistance, and adulthood; antagonism was associated with adulthood, locomotion, and males; play was associated with terrestriality and subadulthood; and travel was associated with locomotion and females. Given that several variables influence bipedalism across multiple behavioral contexts in chimpanzees, it is likely that the early evolution of human bipedalism occurred under the influence of numerous factors. This exploratory study thus suggests that more comprehensive models should be used when reconstructing the transition to bipedalism from the Last Common Ancestor of humans and chimpanzees.