Human hand fine motor control may have evolved to squeeze and test ripe fruit

Chimpanzees use manipulative dexterity to evaluate and select figs, a vital resource when preferred foods are scarce, according to a new Dartmouth-led study just published by Interface Focus. The action resembles that of humans shopping for fruits, and the study demonstrates the foraging advantages of opposable fingers and careful manual prehension, or 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.

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[A]lthough ripe figs come in a range of colors, many stay green throughout development and every phase can be present on a single tree, making it difficult to discern solely by color, which figs are ripe. To determine if the green figs of Ficus sansibarica are edible, chimpanzees ascend trees and make a series of sensory assessments-- they may look at the fig's color, smell the fig, manually palpate or touch each fig (using the volar pad of the thumb and lateral side of the index finger) to assess the fruit's elasticity and/or 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.

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