Unmotivated Subjects Cannot Provide Interpretable Data and Tasks with Sensitive Learning Periods Require Appropriately Aged Subjects: A Commentary on Koops et al. (2022) “Field experiments find no evidence that chimpanzee nut cracking can be independently innovated”

Abstract

In a recent paper in Nature Human Behaviour, Koops et al. (2022) argued that unlike most other chimpanzee “know-how”, nut-cracking falls outside the zone of latent solutions (ZLS). Their conclusion is based on an experiment in which the authors placed nuts and hammers in an area frequented by a wild population of chimpanzees (Pan troglodytes verus) naïve to nut-cracking. Although some of these chimpanzees came into proximity with the provisioned materials, they did not develop nut-cracking. Koops et al. concluded that chimpanzee nut- cracking know-how requires a model to copy – and does not represent a latent solution. We applaud Koops et al.’s efforts to test for the mechanisms that drive nut-cracking in wild chimpanzees, but we argue that their results are inconclusive because the chimpanzees lacked the required test motivation – there was no willingness to eat the nuts, even when their kernels were already exposed. Additionally, most individuals fell outside the age range most likely to foster nut-cracking innovation. For these reasons, Koops et al.’s study outcome is uninterpretable. The question whether nut-cracking is or is not a latent solution in chimpanzees therefore awaits further empirical testing on motivated subjects within adequate age ranges.