Hmmm that’s an interesting question to think about, @michellebannon! As far as I know, there won’t (at least any time soon!) be a unique and distinct third gender.
In animals (which are my favourite thing to think about, most of the time), there are lots of species that can be either male or female. In some cases, they change over the course of their lifetime. Clownfish (like Nemo!), for example, are born as males and then change to females. Other animals (including some coral reef fish) can change back and forth. And others (some slugs and earthworms) can be both at the same time!
All of this is really cool to think about in terms of evolution, and what benefits these different strategies bring to different animals.
I guess some human societies have become very tolerant of diverse sexualities and gender perception, so in some ways we maybe already do have more than the traditional male and female. I dont see a way for evolution to create a third gender that would somehow be required for the reproduction of a species – it would be more costly than just using two or one, and evolution does not tolerate costly solutions.
tough question this one! I would agree with Andrew above that somehow we may already have more than the male and female genders because of the sexuality diversity that exists in our sociaties.