Diversity of Hand Grips and Laterality in Wild African Apes

Comparative studies of primate grasping and manipulative behaviours in captivity have

highlighted, among others, two human abilities that are generally considered unique compared

with other primates: (1) the use of forceful precision and power squeeze grips involving the use

of the thumb, and (2) a species-wide dominant use of one hand (usually the right hand), known

as laterality. However, recent research has highlighted a diversity of precision and power grips in

general among many non-human primates, and there is much debate around the potential for

population-level or species-wide laterality in non-human primates. The majority of this research

to date has been done on captive primates performing specific manipulative tasks, which may

bias or confound these species comparisons. Comparatively little research has been done on hand

use in wild primates, especially during natural, non-manipulative activities, including locomotion.

Here, we investigate hand use during locomotor and non-locomotor behaviours in wild

mountain gorillas ( Gorilla beringei beringei , Bwindi Impenetrable National Park, Uganda), wild

chimpanzees ( Pan troglodytes verus , Taï National Park, Cote d’Ivoire) and chimpanzees kept under

semi-natural conditions ( Pan troglodytes ssp., Chimfunshi Wildlife Trust, Zambia). Preliminary

results propose that hand grips are similar between gorillas and chimpanzees during the

manipulation of common object types. Bwindi gorillas show various hand use strategies during

the processing of several plant foods. Chimfunshi chimpanzees also use forceful precision grips

during daily manipulative tasks, suggesting that this is not a uniquely human ability.