A natural history of human tree climbing.

Walking and running have dominated the literature on human locomotor evolution at the expense of other behaviors with positive and negative fitness consequences. For example, although modern hunter-gatherers frequently climb trees to obtain important food resources in the canopy, these behaviors are seldom considered within the existing framework of primate positional behavior. As a result, inferences about the arboreal performance capabilities of fossil hominins based on a resemblance to humans may be more complicated than previously assumed. Here we use ethnographic reports of human tree climbing to critically evaluate hypotheses about the performance capabilities of humans in trees compared with other primates. We do so by reviewing the ecological basis of tree climbing behavior among hunter-gatherers and the diversity of human climbing techniques and styles. Results suggest that the biological and adaptive significance of human climbing has been underestimated, and that some humans are surprisingly competent in trees, particularly during vertical climbing and activities in the central core of trees. We conclude that while hominins evolved enhanced terrestrial locomotor performance through time, such shifts may have imposed only minor costs on vertical climbing abilities. The diversity of the locomotor repertoire of modern humans must therefore be taken into account when making form-function inferences during the behavioral reconstruction of fossil hominins.