Phenotypic Similarity and Mate Choice

The discussion of what men and women find attractive in the opposite sex would suggest that the characteristics of the person making the choice makes no difference in what they find attractive. Is this true? Well, yes and no. When asked in the abstract what they find attractive, the patterns previously mentioned certainly hold true, but that is not the real world. What kinds of mates do people actually have? When married couples are studied, a somewhat different picture emerges. Although, as we will see, it is consistent with the abstract preference structure.

A common observation of married couples is that they often resemble one another in a variety of phenotypic characteristics at a level significantly greater than expected by chance. For example, taller men tend to be married to taller women and married couples tend to both be overweight or both thin. Married couples also tend to be similar in their IQ scores, personality traits, and many other characteristics. In fact, considering just their faces, married couples tend to resemble each other about as much as male-female first-cousins! The observation that mated males and females resemble each other is called positive assortative mating (PAM). Married couples are not more similar than expected simply because they have been living together and sharing a common physical, social, and intellectual environment. Newlywed couples and even unmarried couples resemble each other as much as couples who have been married for many years.

No one seriously doubts the existence of PAM in humans. The question is whether similarity is attractive or whether similarity is a consequence of other mate choice processes. For example, if similarity is attractive, then we would tend to be drawn to opposite-sex individuals who look most like us. If one happens to be very good-looking, then this process is similar to one in which individuals are attracted to those who match the “ideal” type described above. The interesting case, however, occurs when a below-average individual attempts to make a choice. Do they go for the best possible, or for one that looks like them and is also below-average?

The answer seems to be that people are most attracted to the “ideal,” but then find out how well they can realistically do, and eventually end up with a mate that is similar to them. If the standards for males are similar to those for females, then the sorting out will result in couples that are more similar than would be expected by chance.

If couples are evaluated on a more comprehensive set of traits (not just on their face, for instance), then similarity of overall mate quality becomes very conspicuous. For example, a man of average physical attractiveness who is nonetheless very affluent and attentive may have a composite mate quality score of about the same level as his wife, who is well above average in physical attractiveness but only average in some other traits.