Whether or not nonhuman primates exhibit population-level handedness remains a topic of considerable scientific debate. Here, we examined handedness for coordinated bimanual actions in a sample of 777 great apes including chimpanzees, bonobos, gorillas, and orangutans. We found population-level right-handedness in chimpanzees, bonobos and gorillas, but left-handedness in orangutans. Directional biases in handedness were consistent across independent samples of apes within each genus. We suggest that, contrary to previous claims, population-level handedness is evident in great apes but differs among species as a result of ecological adaptations associated with posture and locomotion. We further suggest that historical views of nonhuman primate handedness have been too anthropocentric, and we advocate for a larger evolutionary framework for the consideration of handedness and other aspects of hemispheric specialization among primates.

Predominance of right-handedness has historically been considered as a hallmark of human evolution. Whether nonhuman primates exhibit population-level manual bias remains a controversial topic. Here we investigated the hypothesis that bimanual coordinated activities may be a key-behavior in our ancestors for the emergence and evolution of human population-level right-handedness. To this end, we collected data on hand preferences in 35 captive gorillas (Gorilla gorilla) during simple unimanual reaching and for bimanual coordinated feeding. Unimanual reaching consisted of grasping food on the ground while bimanual feeding consisted of using one hand for holding a food and processing the food item by the opposite hand. No population-level manual bias was found for unimanual actions but, in contrast, gorillas exhibited a significant population-level right-handedness for the bimanual actions. Moreover, the degree of right-handedness for bimanual feeding exceeds any other known reports of hand use in primates, suggesting that lateralization for bimanual feeding is robust in captive gorillas. The collective evidence is discussed in the context of potential continuity of handedness between human and nonhuman primates. Keywordshandedness; hemispheric specialization; unimanual reaching; bimanual coordination; primates A universal human behavioral trait is right-handedness (Perelle and Ehrman, 1994;Annett, 2002;Raymond and Pontier, 2004). Although there is some variation between different cultures, all human populations studied to date have been shown to display right hand preferences, particularly for complex motor actions (e.g., Fagard, 2001). Moreover, the archeological data suggest that right-handedness in tool use can be dated back at least 2.5 millions years ago (Corballis, 1991;Bradshaw and Rogers, 1993). Whether evidence of handedness can be dated back even further in Hominid evolution, particularly in our closest living relative, the great apes, remains a topic of intense debate (McGrew and Marchant, 1997;Hopkins, 2006 Whereas historically population-level behavioral and hemispheric specialization have been considered hallmarks of human evolution (Warren, 1980;Ettlinger, 1988;Crow, 2004), there is a growing body of evidence of population-level behavioral and brain asymmetries in a host of vertebrates (Rogers and Andrew, 2002;Vallortigara and Rogers, 2005;Hopkins, 2007). For example, population-level limb preferences for motor actions have been found in some species of toads, rats and dogs, suggesting some phylogenetic continuity between animal species (Hook, 2004 for review). However, not all species show the same patterns and some have been critical of both the methods and interpretation of results in nonprimate species with respect to evolutionary models of handedness (MacNeilage et al., 1987;Crow, 2004). It is in this regard that studies of handedness in nonhuman primates have become increasingly important for testing and evaluating different evolutionary and genetic models of handedness (Hopkins, 2004(...

Understanding the relationship between physical environments and nonhuman primate behavior is a key element for effective care and management in a range of settings. The physical features of the captive environment, including not only gross useable space but also environmental complexity, can have a significant influence on primate behavior and ultimately, animal welfare. But despite this connection, there remains relatively little conclusive data on how captive primates, especially great apes, use the spaces provided to them, especially in modern, indoor-outdoor enclosures that have become more prevalent in recent years. In this study, we used four years of detailed data on where 23 great apes (chimpanzees and gorillas) positioned themselves within a modern, indoor-outdoor zoo enclosure to determine not only how the apes utilized their space but also how access to outdoor areas affected their spatial selectivity. We found that both species used relatively little of their available space: chimpanzees and gorillas spent half their time in only 3.2 and 1.5% of their useable three-dimensional space, respectively. Chimpanzees utilized the outdoor space more than gorillas, but access to the outdoors did not affect space selectivity in the indoor area for either species. Although both species of ape were highly selective in their space use, consideration should be given to the importance of providing the choice to locate in a variety of spaces, including outdoor areas. These data represent an extremely detailed account of space selectivity by great apes in an indoor-outdoor environment and have substantial implications for future facility design and captive primate management.

In both humans and other species, many decisions involve risk, which is defined as uncertainty about whether an investment will result in a cost or benefit (Yates & Stone, 1992). Often, risky decisions in the animal kingdom include those involving resources, encompassing decisions about how far to travel for food or water (Smallwood, 1996). This is a form of economic risk, as animals must minimize the cost of foraging and optimize resource acquisition when a positive outcome is not guaranteed. Social interactions can also result in costs and benefits, but here, the other individual often determines the outcome. Consequently, many social interactions are characterized by uncertainty (Bohnet, Greig, Herrmann,

As a result of environmental variability, animals may be confronted with uncertainty surrounding the presence of, or accessibility to, food resources at a given location or time. While individuals can rely on personal experience to manage this variability, the behavior of members of an individual's social group can also provide information regarding the availability or location of a food resource. The purpose of the present study was to measure how captive chimpanzees individually and collectively adjust their foraging strategies at an artificial termite mound, as the availability of resources provided by the mound varied over a number of weeks. As predicted, fishing activity at the mound was related to resource availability. However, chimpanzees continued to fish at unbaited locations on the days and weeks after a location had last contained food. Consistent with previous studies, our findings show that chimpanzees do not completely abandon previously learned habits despite learning individually and/or socially that the habit is no longer effective.