Humans often behave in an altruistic manner, even to completely unrelated strangers. From economics to evolutionary biology, researchers have investigated what mechanisms underlie such altruism. Recent findings show that even irrelevant pictures of eyes make people more generous. This phenomenon is typically explained by claiming that images of eyes, by inducing feelings of being watched, trigger social evaluation and reputation concerns. In an experiment, we show that the effect of pictures of eyes cannot be explained by this mechanism. Although pictures of eyes increase pro-social behavior in interaction tasks, they do not influence decisions in individual decision making tasks. This stands in sharp contrast to past findings on social evaluation and to the results obtained from a comparison treatment designed to trigger social evaluation concerns. Our results, however, can be explained by the role that eyes play in relations of dominance and submissiveness, as found both in animal and human studies. This suggests that research on altruism should not focus solely on higher level social constructs such as reputation building, but also consider the impact of more primitive, lower level instincts.