More than a decade before there were systematic etnpirical tests of the proposition, evolutionary psychologists hypothesized that men and women would differ psychologically in the weighting given to the cues that trigger sexual jealousy (Daly, Wilson, & Weghorst, 1982: Symons, 1979). Because fertilization occurs internally within women, over hutnan evolutionary history men have recurrently faced an adaptive problem not faced by women—the problem of uncertainty in their genetic parentage of offspring. Sexual infidelities by a man's mate would have compromised his paternity, threatening the loss of his investments, commitments, and mating effort, as well as his partner's parental effort—all of which risked getting channeled to another man's children. Men's jealousy, therefore, has been hypothesized to be triggered by cues to .sexual infidelity. Over human evolutionary history women did not face the adaptive problem of maternity uncertainty. The internal fertilization of a woman's own eggs meant that the certainty in her genetic parentage did not deviate from 1009?. From an ancestral woman's perspective, however, infidelities by her regular mate could have been enormously damaging. The man's time, energy, commitment, parental investment, and resources could get channeled to another woman and her children. For these reasons, evolutionary psychologists have hypothesized that women's jealousy would be triggered by cues to the long-term diversion of such commitments, such as a man's emotional involvement with another woman (Daly et al., 1982; Symons, 1979). Emotional involvement and sexual infidelity are clearly correlated events in everyday life, and hence both sexes are predicted to be attuned to both sources of strategic interference (Buss, 1989; Buss, Larsen, Westen, & Semmelroth, 1992). But these events can and do occur without one another: A casual sexual encounter need not entail emotional involvement, and deep emotional involvement can occur in the absence of sexual intercourse. The sexes are predicted to differ in the weighting of the cues to these two kinds of infidelity, with men more intensely focused on sexual and women on emotional infidelity. DeSteno and Salovey (DS, this issue) have proposed an alternative explanation, the hypothesis, to account for empirically discovered sex differences corresponding to the evolutionary predictions. Harris and Christenfeld's (HC, this issue) logical belief is a variant of this alternative. The double-shot hypothesis proposes that the obtained sex differences are due not to evolved psychological differences, but rather to different beliefs (in some groups of men and