Introduction

In 1974 I presented findings on faunivory, tool-use and food-sharing by chimpanzees to a Wenner-Gren Foundation symposium on the Great Apes. Some of the data were mine, but most were trawled from the treasure trove at Gombe begun by Goodall (1968, 1986). The paper was eventually published (McGrew, 1979), but in the intervening 5 years the picture changed notably, and it has changed even more so in the last 10 years.

The data reported in 1974 were the first to indicate differences between the sexes in an adaptive suite of hominoid subsistence activities. Several others sought to tackle the implications of these issues in the 1970s (Isaac, 1978a; Tanner & Zihlman, 1976; Zihlman, 1978). What follows is a synthesis and updating of their views from the usefully detached position of the armchair and of my views from the position of a chimpanzee field-worker. Case studies from Gombe will be used as convenient take-off points. The over-riding question is: How would a proto-hominid population make the transition from sex differences in diet to sexual division of labour in subsistence?

Sex is arguably the most important independent variable in evolutionary biology. It is one of life's few simple dichotomies, and leads to some equally stark consequences; consider the old saw that no organism is ever only partly pregnant. Given this, one might expect studies of behavioural sex differences in hominoids, that is, the phenotypic expression of behavioural traits ultimately linked to the two types of chromosome, to be straightforward. They are not.