health
transient males. Since these loyal males already bond and cooperate with females, it may well be a simple matter for them to bond and cooperate with each other. In a semi-counter intuitive manner, the ability to bond with males could be selected for based on its effect on reproductive success with females. On the other hand, a male that commits himself to a cooperative loyal and exclusive arrangement with a female necessarily limits his interactions One of the most robust and reliable findings in with other females. This implies that he will attempt to insure the scientific literature on interpersonal that the offspring he is raising are genetically related to him. attraction is the overwhelming role played by physical attractiveness in defining the ideal Of course, another possibility is that a loyal male may be romantic partner Hatfield & Sprecher, 1986; attractive to multiple females, who in turn compete for his Jackson, 1992 . Both men and women express attention and loyalty. Clearly the outcome of such interactions marked preference for an attractive partner in a is influenced by how many females can the male effectively non- committed short-term casual, one night stand relationship Buss & Schmitt, 1993 . protect that is, improve their reproductive success . The situation quickly gets complex and many competing strategies are possible. Different species make different choices depending upon their evolutionary history and environmental constraints. As we noted above, secondary sexual characteristics, that is, traits that vary dramatically between the two sexes, serve to advertise various traits, including heath, loyalty, robustness, and fertility. The size and symmetry of a beetles or an elks antlers or a grasshoppers song communicate rather clearly their state of health.192 The tail of the male peacock is a common example, a male either has large, colorful and symmetrical tail, all signs of a health or it does not there is little room for ambiguity. These predictions have been confirmed experimentally in a number of systems; the robustness of offspring does correlate with the robustness of the male, a win for evolutionary logic.193 It is critical that both females and males correctly read and/or respond to various traits, and this ability is likely to be selected for. For example, males that can read the traits of other males can determine whether they are likely to win a fight with another male; not being able to make such an accurate determination could result in crippling injuries. A trickier question is how does a female or a male determine whether a possible mate will be loyal? As with advertisements of overall robustness, we might expect that traits that are difficult or expensive to generate will play a key role. So how.