Assortative mating: sex differences in mate selection for married and unmarried couples.

We studied assortative mating for age, nationality, educational level, and occupational level in married and unmarried parents to test evolutionary models explaining mate selection among humans. We used the marriage and birth registers of the Venezuelan population to compare recently married, fertile married, and fertile unmarried couples. The results show significant assortative mating for all variables, but the results are strongest for age and education. These data suggest that (1) selection criteria based on age vary along the life cycle and differ between married and unmarried couples; (2) male's socioeconomic status is more related to the availability of younger females among unmarried couples compared with married couples, except for young couples; and (3) female selection for better (more educated and/or better employed) mates is stronger among married couples, whereas male selection for younger females or those showing actual reproductive potential is stronger among unmarried couples.