Assortative Mating

Primarily used in reference to evolution, assortative mating refers to animals and people tending to mate with others with similiar traits regarding age, intelligence, education, wealth, ethnic origin, height, occupation, religion, place of birth, and race.
Positive assortative mating is the marriage of likes to likes.
Negative assortative mating is the marriage of likes to unlikes.

Also Known As: Assortative pairing, marriage of likes to likes

Examples:

"... assortative mating shapes the characteristics of families and, to the extent that social attributes are inherited or learned from parents, the population composition of the next generation."

Source: How Do Marriage, Divorce, and Educational Upgrading Affect Trends in Educational Assortative Mating?