Biological sex differences have long been used as arguments justifying male dominance and sexist oppression. Animal studies of sex differences are used to claim that human sex roles have a long evolutionary history. For example, in a study of toy preferences invervet monkeys, the authors conclude that sex-differentiated object preferences arose early in human evolution. In this paper I scrutinize the study and reveal that both the hypotheses, the performed preference tests and the conclusions drawn are flawed. In the study, the authors hypothesise that male vervets should prefer a ball and a car based on the human hunter-gatherer hypothesis. Men are suggested to be selected for navigating abilities useful for hunting and women for nurturing babies. This hypothesis is then transferred to vervets which is a tree-living species, subsisting of a mainly vegetarian diet, where skills such as navigating in space ought to be necessary for survival - in both males and females. Furthermore, the presentation of toys is conducted in groups, individual interactions with a toy is taken as a preference for the sex of that individual. Therefore it is impossible to derive individual preferences from these tests. Vervets are matrilinear with females sometimes being dominant to males. From an animal behaviour framework, I would interpret the preferences as an interaction between individuals. Perhaps low-ranked individuals approach new objects first, as they may be dangerous. The results are interpreted and presented with graphs and pictures in order to tell the convincing story about sex differences in toy preference that the authors wanted to find, but there is but there is weak support for these conclusions. Hence, from the evidence presented in this study, we cannot conclude that human sex-differentiated toy preferences date more than 23 million years back in time.