There is an actual third gender. That is true hermaphroditism. Some humans are true hermaphrodites. The most common cause of this? 2 eggs fusing, 1 male and 1 female before they start differentiation.

These have both male and female characteristics and so they can't be classified as either male or female.

There is an actual third gender. That is true hermaphroditism. Some humans are true hermaphrodites. The most common cause of this? 2 eggs fusing, 1 male and 1 female before they start differentiation.

These have both male and female characteristics and so they can't be classified as either male or female.

Here is my source:

https://en.wikipedia.org/wiki/True_hermaphroditism