There are more than two genders.
I believe that there are only two genders for humans, but there are more than two in other species. (I know your thinking this is cheap, but the question never specified). For example there is a type of fungi that has 36,000 different genders. There is a type of jelly fish that can actually change gender. Also in Latin (maybe this is a little cheap) there are three genders Masculine, Feminine, Neuter.