Homosexual (as well as bisexual) behavior is wiespread in the animal kingdom. Animal sexual behavior takes many different forms, even within the same species and the motivations for and implications of their behaviors have yet to be fully understood as most species have yet to be studied. A 1999 review by researcher Bruce Bagemihl shows that homosexual behavior, not necessarily sex, has been observed in close to 1500 species, ranging from primates to gut worms, and is well documented for 500 of them.