Laterality of hand function in naturalistically housed chimpanzees (Pan troglodytes)

Abstract

Studies of laterality of hand function in chimpanzees (Pan troglodytes) have the potential to tell us about the origins of handedness in Homo sapiens. However, the data are confusing, with discrepancies present between studies done in the field and the laboratory: the former show wild chimpanzees to be unlateralised at the population level, while the latter show captive chimpanzees as lateralised at the population level. This study of 26 semi-free ranging chimpanzees of Chester Zoo, UK, aimed to investigate a situation between the wild and captivity and provided ethological data for 43 categories of spontaneous manual use and 14 categories of tool use. Other variables recorded were subordinate hand activity, whether the subject was arboreal or terrestrial, and the identity of the subject. Using switching focal subject sampling, 23,978 bouts of hand use and 1,090 bouts of tool use were recorded. No population-level handedness was present for manual non-tool use activities in the naturalistically housed chimpanzees of Chester Zoo in a similar way to studies of wild chimpanzees. However, about half of the individuals were lateralised to one side or the other for the foraging behaviours of pick up, eat, and pluck. Using a modified version of McGrew and Marchant's (1997) Laterality Framework, these results are comparable to some wild and captive populations for similar foraging tasks. Bimanuality was rare and thus prevented comparison with captive experimental studies that have reported population right handedness. Behaviour involving contact with water elicited stronger lateralisation. Chester chimpanzees were more likely to exhibit hand preferences for manual tasks with increasing age but there were no effects of sex or rearing history on hand specialisations in adult individuals. Lateralisation was biased in tool use, which evoked significant left hand preferences in half the individuals, with no effect of age. Results are discussed comparatively with reference to methodological and developmental issues. Longitudinal studies of hand use are needed to increase our understanding of laterality of hand use in chimpanzees.

Handedness in Captive Bonobos (Pan paniscus)

“…The distinction between species level and population level preferences is important. Each approach, although equally valid, addresses different questions: species level shows that handedness is fixed genetically, whereas population level indicates that there is flexibility in the genetic control of handedness, where environmental factors might have greater influence on the expression of handedness [Fletcher and Weghorst, 2005]. If the evolution of human handedness is the main aim of investigation, then finding a species level preference must be the goal.…”

“…However, other studies, particularly of wild populations, have not found significant hand preference [Heestand, 1986;Hopkins, 1993;Hopkins et al, 1993a;Marchant and McGrew, 1996;McGrew and Marchant, 2001;Marchant and McGrew, 2007]. A comprehensive study of naturalistically housed chimpanzees replicating the methods used in studies in the wild [Marchant and McGrew, 1996;McGrew and Marchant, 2001] found that the population as a whole was largely unlateralised [Fletcher and Weghorst, 2005].…”

Wild chimpanzees show population-level handedness for tool use

“…Rearing chimpanzees by righthanded humans presumably causes captive-born chimpanzees to be more right-handed than wild-born individuals. As a means of testing this hypothesis, the HI scores from the combined wild chimpanzee data were compared with the HI scores provided in three previously published reports of hand use for tool-use tasks in captive chimpanzees (n ϭ 29) that mimic the demands of termite-fishing in wild chimpanzees (49)(50)(51)(52). In the captive studies, the chimpanzees needed to probe with sticks to extract food (yogurt or honey) from an artificial termite mound.…”

Comparative and familial analysis of handedness in great apes.

“…For example, in the two studies of handedness in wild chimpanzees with the largest sample sizes McGrew & Marchant, 2001), hand use for daily actions was measured. Hand use in each study was based on the 10 or 15 most frequent behaviors, all of which were behaviors that did not induce significant preferences at the individual level (see also Fletcher & Weghorst, 2005). These behaviors included scratch, groom, eat, pluck, pull, nose wipe, pincer, pick up, hold, and cradle.…”