Why, when your brother brings his girlfriend and his wife, do you suddenly feel that she seems pretty good? It’s not because your taste suddenly changed. It’s because, in human evolution, there’s a psychological mechanism called “mate choice copying.” In simple terms, when we assess the value of a potential partner, we’re not relying entirely on our own observations—we also unconsciously reference other people’s choices. When someone has already been chosen by others, especially chosen by someone you consider worthy and valuable, the brain treats that “being chosen” as a form of social validation: since someone is willing to invest time, feelings, and costs to build a relationship with her, she likely has certain strengths you hadn’t noticed before. It’s like looking at sales figures and reviews when shopping, or following the judgment of skilled investors when investing—because others have already done part of the filtering for you. Research finds that both men and women are affected by this. A person who would originally be considered ordinary may, after entering a relationship that others recognize, seem more attractive to other people. But mate choice copying isn’t simple imitation; it’s an information shortcut humans use to reduce the cost of judgment in complex environments. We use other people’s choices to quickly infer a person’s hidden value. So many times, the attraction we feel doesn’t come entirely from the other person herself—it also comes from the signal that “this person has already been chosen by someone else.”