 However, just as in non-human behavioral ecology, differences between the predicted and described behavioral strategies require scientists to build new models, or suggest additional conditions or constraints to add to the original models; there must be independent evidence that these conditions or constraints obtain. Kaplan and Hill’s observations do depart from what their model predicts: the Ache engage in a number of prey choice decisions that are not obviously fitness maximizing. In particular, men often seem to ignore many calorie rich food sources from plants and sometimes smaller animals, and women do not pursue larger game. The question then is how to proceed: HBEs often suggest changes to the model that might account for these failures of prediction; often, they do give some independent evidence for their suggestions. For example, one of Hawkes’ proposed explanations for why male hunting behavior often fails to meet prey choice expectations (similar failures are found in many societies besides the Ache) is that men pursue large game for reasons other than merely collecting calories—they are also interested in showing off in order to get other fitness rewards, such as additional sexual partners or better alliances with other men. Hawkes was able to show that men’s prey choice decisions were consistent with this view (Hawkes, 1991).