A couple weeks ago, a transgender dog made the news. The Pomeranian puppy was born with both male and female reproductive organs. The dog needed a $1,165 gender reassignment surgery to prevent infection and reduce the dog’s risk of developing cancer. While the puppy would be better described as intersex than transgender, it certainly shows that sex is not binary in nature.

And now, the news has shifted to Canada’s transsexual fish. (No, the fish haven’t undergone gender reassignment surgery.) Chemicals from human trash, which include endocrine disrupters, have impacted the sexual development of fish. The chemicals have been causing male fish to exhibit elevated levels of a protein that normally only exists in females when they’re producing eggs. Even more startling, in the areas of the water affected by pollution, 85% are female (compared to 55% female in the water without chemical pollution).

Okay, so the “transsexual fish” are actually just a case of human interaction harming animals. But is sexual variance common among animals?

study on intersex pigs confirmed that there is a complete spectrum of types of intersex pigs, similar to the variation of intersex people. Another study discussed intersex red claw crayfish — apparently male and female sexual organs can appear in different combinations in crayfish. According to the study, some of the intersex crayfish were acting as functional females, despite having sexual variations. Scientists have also studied intersex goats, dogs, and horses.

Basically, many (if not all) animals have some intersex members. If the sex binary is so natural, why doesn’t it exist in nature?

Fish are even more interesting. Many fish can quickly change sexes in order to maximize their fertility. Some species can even switch between producing eggs and producing sperm several times during a single mating.

Having two distinct sexes does not necessarily benefit a species. (In fact, sex changes are an integral part of the survival of some species.) Some people argue that dividing people into male and female or man and woman is just a convention based on nature. That is simply untrue. Animals — including humans — naturally exhibit a variety of sexes.

Photo credit: nerissa’s ring