Mating between closely related individuals, the extreme condition being self-fertilization, which occurs in many plants and some primitive animals. A population of inbreeding individuals generally shows less variation than an outbreeding population. Continued inbreeding among a normally outbreeding population leads to inbreeding depression (the opposite of hybrid vigour) and an increased incidence of harmful characteristics. For example, in humans, certain mental and other defects tend to occur more often in families with a history of cousin marriages.
Subjects: Biological Sciences.