Defining Assortative Mating and the Empirical Evidence
Assortative mating is a phenomenon studied in evolutionary psychology, sociology, and behavioural genetics: individuals with similar characteristics pair up with one another at a higher rate than random pairing would produce. It is observed across a wide range of traits, but its strength varies considerably from one trait to another. The strongest similarity of all appears for age, and clear similarity is also reported for traits bound up with values and social background, such as religion, educational attainment and political attitudes. Similarity on intelligence and physical attractiveness is weaker than that, and assortment on personality traits is reported to be weaker still, with couples showing nothing like the strong similarity found for attitudes and values. The usual explanation is that personality traits are harder to observe from the outside and are therefore not readily evaluated during the early stages of partner selection.
The Mechanisms Behind Assortative Mating
Several distinct explanations have been offered for how assortative mating comes about. (1) Active assortment: people consciously prefer partners who resemble them, since the similarity hypothesis holds that we are drawn to those who are like us. (2) Social homogamy: similar people are concentrated in the same social settings such as schools, workplaces, and neighbourhoods, so opportunities for meeting are skewed from the outset. (3) Convergence: partners grow more alike over long years of shared life, although research indicates that the convergence effect is small. (4) Market constraints: within the partner market, people are matched with others of roughly comparable "market value," and assortment on physical attractiveness is partly explained by this mechanism. In reality several of these mechanisms operate at the same time, and which one predominates differs from trait to trait.
What Assortative Mating Implies for Compatibility Assessment
The findings on assortative mating offer a useful lens for looking back at how you chose a partner. People drift toward those who resemble them without having to try, so the parts where you feel you simply click are usually the parts that were already alike before you ever met. If that is so, what is worth checking is not the similarity but the mismatches you have not yet put into words. A second thing worth knowing is that some dimensions align easily and others do not. Closeness in age, in social background, in religion and in political outlook tends to be settled at the point of meeting. Compatibility of personality, by contrast, is hard to see from the outside and often becomes apparent only some way into a relationship, which means it stays buried unless you deliberately raise it. It is also worth holding on to the observation that the pull toward similar partners has been implicated in entrenching social inequality: narrowing your choices on similarity alone will not always produce the better outcome.