Many researchers have looked into this problem. Statisticians rely on probabilistic models, which are summarized in the “37 percent rule”: if you have one hundred candidates, check the first thirty-seven to get a sense of what they all look like, and then from number thirty-eight on choose the first one that is better than all of the previous thirty-seven. Biologists can tell us how partnering animals make their choices: They first estimate their own attractiveness by getting feedback from members of the opposite sex. An offer from a good-looking potential mate might raise their level of aspiration; a rejection from an inferior one would lower it. After an “adolescence” involving some twenty interactions, they figure out which of their fellow species they can realistically aim for and settle down into stable relationships.