Assortative mating (also referred to as positive assortative mating or homogamy) is a mating pattern and a form of sexual selection in which individuals with similar phenotypes or genotypes mate with one another more frequently than would be expected under a random mating pattern.
A majority of the phenotypes that are subject to assortative mating are body size, visual signals (e.g. color, pattern), and sexually selected traits such as crest size.
Homophily (from Ancient Greek ὁμός (homós) 'same, common' and φιλία (philía) 'friendship, love') is a concept in sociology describing the tendency of individuals to associate and bond with similar others, as in the proverb "birds of a feather flock together". The presence of homophily has been discovered in a vast array of network studies: over 100 studies have observed homophily in some form or another, and they establish that similarity is associated with connection. The categories on which homophily occurs include age, gender, class, and organizational role.
The opposite of homophily is heterophily or intermingling. Individuals in homophilic relationships share common characteristics (beliefs, values, education, etc.) that make communication and relationship formation easier. Homophily between mated pairs in animals has been extensively studied in the field of evolutionary biology, where it is known as assortative mating. Homophily between mated pairs is common within natural animal mating populations.
Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the harmful effects of inbreeding. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating and natural and sexual selection, in order to prevent breeding among related individuals. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of such mechanisms.
Inbreeding can result in inbreeding depression, which is the reduction of fitness of a given population due to inbreeding. Inbreeding depression occurs via appearance of disadvantageous traits due to the pairing of deleterious recessive alleles in a mating pair's progeny. When two related individuals mate, the probability of deleterious recessive alleles pairing in the resulting offspring is higher as compared to when non-related individuals mate because of increased homozygosity. However, inbreeding also gives opportunity for genetic purging of deleterious alleles that otherwise would continue to exist in population and could potentially increase in frequency over time. Another possible negative effect of inbreeding is weakened immune system due to less diverse immunity alleles as a result of outbreeding depression.
Homogamy is marriage between individuals who are, in some culturally important way, similar to each other. It is a form of assortative mating. The union may be based on socioeconomic status, class, gender, caste, ethnicity, or religion, or age in the case of the so-called age homogamy.
It can also refer to the socialization customs of a particular group in that people who are similar tend to socialize with one another.