The world’s coral reefs are the greatest producer of diversity on the planet, and that diversity includes gender variation.
In the wonderful Pixar movie Finding Nemo, Nemo’s mother is killed in the first scene. The rest of the movie is about the relationship between the surviving father and son clown fish.
Except that is not what happens for real clown fish. Real clown fish switch genders. As portrayed in the movie, clown fish live in a single anemone in monogamous breeding pairs of one larger female and a smaller male, along with some juveniles. However, in real clown fish lives, if the female dies, the adult male changes into a female, and one of the juveniles becomes an adult male. So… Nemo’s father should have become the larger female, and Nemo should have become his father’s, now wife’s, husband. That certainly would have made a more surprising movie.
I imagine Pixar had some lively meetings talking through the human-like story they wanted to tell using fish who have a very different idea of family building.