Homosexual behaviour has also been seen in animals. Homosexual, transgender and bisexual behaviour includes sex, courtship, affection, pair bonding, and parenting. Homosexual behaviour is widespread among animals. Bruce Bagemihl did research in 1999. It shows that homosexual behaviour has been observed in close to 1500 species, from primates to gut worms, and is well documented for 500 of them. The sexual behaviour of animals takes many different forms, even within the same species. The motivations for these behaviours are only partly known, mainly because the respecive species has not been fully studied yet. According to Bagemihl, "the animal kingdom [does] it with much greater sexual diversity—including homosexual, bisexual and nonreproductive sex—than the scientific community and society at large have previously been willing to accept."