Assortative mating, also known as homogamy or positive assortative mating, is a non-random mating pattern where individuals with similar phenotypes or genotypes mate more frequently than expected under random mating. This form of sexual selection can influence the genetic structure and evolution of populations. The opposite of assortative mating is disassortative mating, where individuals with dissimilar traits mate.
Assortative mating can be positive, where similar individuals mate, increasing the frequency of shared traits and leading to a more homogenous gene pool. It can also be negative (disassortative), where dissimilar individuals mate, promoting diversity and a wider range of allele frequencies. Examples of traits subject to assortative mating include body size, visual signals like color, and sexually selected traits such as crest size. In humans, assortative mating occurs based on factors like education, physical traits, cultural background, and even genetic similarities. Studies have found correlations between genetic markers for height and BMI in couples.
The causes of assortative mating vary across species and can include intrasexual competition, where larger males compete for larger females. It can also arise from social competition, where individuals with similar competitive abilities are more likely to mate. Assortative mating can lead to reproductive isolation and potentially contribute to speciation over time. Plant and animal breeders commonly use assortative mating to select for desired traits.
Although often attributed to conscious preferences, assortative mating can also result from structural causes and social dynamics. Research indicates that assortative mating increases relatedness within families and may enhance offspring survival if the selected traits remain beneficial.
