Kin recognition (kin detection) is animals' abilities to distinguish between close genetic kin and non-kin. In evolutionary biology and in psychology, such capabilities are presumed to have evolved to serve the adaptive functions of kin altruism (see kin selection) and inbreeding avoidance. Apart from a few exceptional cases, such as the green-beard effect, kin recognition is achieved via several cue-based mechanisms, such as imprinting and phenotype matching. Because kin recognition is cue-based, errors sometimes occur. A well known example is the Westermarck effect in which unrelated individuals who spend their childhood in the same household find each other sexually unattractive.