the causes of homosexuality and bisexuality are controversial (people do not agree on them). the causes of homosexuality are not all understood, but genetics and the effects of the prenatal environment and hormones (when a baby is growing in its mother) are thought to be causes. there is not much evidence that the social environment is a cause of homosexuality. scientists also show that homosexuality happens not only in humans. some animals (like penguins, chimpanzees, and dolphins) often show homosexuality, and some (rams) even for lifelong periods as is the case with humans.