Women, like female weaverbirds, prefer men with desirable “nests.” Consider one of the problems that women in evolutionary history had to face: selecting a man who would be willing to commit to a long-term relationship. A woman in our evolutionary past who chose to commit to mate with a man who was flighty, impulsive, philandering, or unable to sustain relationships found herself raising her children alone, without benefit of the resources, aid, and protection that another man might have offered. A woman who preferred to mate with a reliable man, one willing to commit to her over the long run, was more likely to have children who survived and thrived. Over thousands of generations, a preference for men who showed signs of being willing and able to commit to them evolved in women, just as preferences for mates with adequate nests evolved in weaverbirds. This preference solved key reproductive problems, just as food preferences solved key survival problems. People do not always desire the commitment required of long-term mating. Men and women sometimes deliberately pursue a short-term sexual strategy—a brief fling, a one-night hookup, a weekend liaison, or a casual affair. And when they do, their preferences shift, sometimes dramatically. One of the crucial decisions for humans in selecting a mate is whether they are seeking a short-term mate or a long-term partner, a partner in whom they invest little or a partner to whom they commit a lot. The sexual strategies pursued hinge on this decision.