New York, April 22: The way we shop and bargain for fruits and vegetables using our sensory powers, chimpanzees too use manipulative dexterity to evaluate and select figs -- a vital resource when preferred foods are scarce, say researchers.
The study demonstrates the foraging advantages of opposable fingers and careful manual prehension (the act of grasping an object with precision).
The findings shed new light on the ecological origins of hands with fine motor control, a trait that enabled our early human ancestors to manufacture and use stone tools.
"The supreme dexterity of the human hand is unsurpassed among mammals, a fact that is often linked to early tool use," said lead author Nathaniel J Dominy, professor of anthropology at Dartmouth College in the US.
For the study, Dominy and his colleagues observed the foraging behaviours of chimpanzees, black-and-white colobus monkeys, red colobus monkeys and red-tailed monkeys in Kibale National Park, Uganda.
The primates depended on figs. To determine if the green figs are edible, chimpanzees ascend trees and make a series of sensory assessments.
They look at the fig's colour, smell the fig, manually palpate or touch each fig to assess the fruit's elasticity and bite the fig to determine the stiffness of the fruit.
Colobus monkeys do not have thumbs and evaluate the ripeness of figs by using their front teeth.
The team observed the non-selection, rejection and ingestion of individual figs by chimps and collected specimens of figs.
Based on the sensory data obtained, the team estimated the predictive power that sensory information may have on chimpanzees when estimating the ripeness of figs.
The study, published in the journal Interface Focus, resembles that of humans shopping for fruits and provides new insight into how chimpanzees exhibit advanced visuomotor control during the foraging process and more broadly, on the evolution of skilled forelimb movements.