Are there any lifeforms on earth that have more than male and female biological sexes?
If so, are all three mates required for reproduction or is there something else going on?
If not, why not? There are species that have one sex and there are species with 2 sexes. I get some of the basics of why there are two instead of one, but would those benefits not be even greater if there were three sexes?
NOTE: I am of course only talking about sexual reproduction. I have no intention or desire to talk about transgender or LGBT issues nor am I wanting to make any points on the issue. This is solely a question about sexes in biology and not human social constructs.
Also, I am a computer programmer, not a biologist. Please forgive me for not knowing any of the terminology.