First, gay males tend to be born later in birth order and often have older brothers, suggesting the presence of viable kin as potential foci of kin investment. (p.251)
Women judge sexually free women to be so undesirable because they realize that available women can pose a great threat to their committed relationships. (p.263)
Two tactics, however, are specially tailored to enticing mates from others. The first is temporal invasion, acts such as changing one's schedule in order to be around the target more than the target's current partner, or dropping by when the current partner is off at work or out of town.
The second is driving a wedge - insinuating oneself into the existing mateship and actively promoting a breakup. One way to drive a wedge is to boost the target's self-esteem, conveying messages that enhance their self-perceptions of their own desirability. At the same time, the poacher might communicate that the target is not appreciated by their regular partner: "He doesn' t treat you well" or "You deserve better" or "You' re too good for him. "The simultaneous boost in self-esteem combined with the contrast of feeling under appreciated is sometimes enough to succeed in widening a small crack in a relationship.(p.265-266)
When imagining an emotional infidelity, for example, women's skin conductance, heart rate, electromyographic activity, and body temperature all shoot up - physiological events that are highly correlated with the subjective reports of actual distress. Men show greater physiological distress when imagining a partner trying out different sexual positions with a rival. (p.267)
( David M. Buss – The Evolution of Desire )
