Assortative mating is a mating pattern, and a type of sexual selection, that impels individuals to mate with other individuals that share physical characteristics, referred to as genotypes and phenotypes (age, size, coloration, pigmentation, etc), than would be expected in random mating patterns.
For instance, in a wolf pack only the alpha male and alpha female mate. Becoming the ʺalphaʺ in a pack generally means being the largest, strongest, healthiest and most dominant members of the pack thereby passing along these positive traits to the next generation in a practice known as homogamy. This pattern of mating increases the positive familial traits. Non-assortative mating, or individuals of varying genotypes/phenotypes mating is less common than assortative mating and decreases the shared familiar traits.