Possible causes of sex differences in the use of natural hammers by wild chimpanzees
The wild chimpanzees of the Tai National Park, Ivory Coast, present an important sex difference in nut-cracking behavior: Adult females more frequently perform the two most difficult techniques, coula cracking in the tree and panda cracking. Adult females are more efficient than males in all the three nut-cracking techniques for one or the other measure of efficiency (number of hits/nut and number of nuts opened/min). The analysis of 5 hypotheses which may explain these differences, stresses the role of the difference of sociability and sexual dimorphism between the sexes, both negatively affecting the nut-cracking techniques and performance of the adult males. We shall discuss the role of these factors on the evolution of the division of labor and food-sharing in the chimpanzee and in early hominids.