Various non-human animal species exhibit behavior that can be interpreted as homosexual or bisexual, often referred to as same-sex sexual behavior (SSSB) by scientists. This may include same-sex sexual activity, courtship, affection, pair bonding, and parenting among same-sex animal pairs. Various forms of this are found among a variety of vertebrate and arthropod taxonomic classes. The sexual behavior of non-human animals takes many different forms, even within the same species, though homosexual behavior is best known from social species.
Scientists observe same-sex sexual behavior in animals in different degrees and forms among different species and clades. A 2019 paper states that it has been observed in over 1,500 species. Although same-sex interactions involving genital contact have been reported in many animal species, they are routinely manifested in only a few, including humans. Other than humans, the only known species to exhibit exclusive homosexual orientation is the domesticated sheep (Ovis aries), involving about 10% of males. The motivations for and implications of these behaviors are often lensed through anthropocentric thinking; Bruce Bagemihl states that any hypothesis is "necessarily an account of human interpretations of these phenomena".
