system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why did two sexes become the norm for species instead of three or more?
gpt
The whole reason for sex (and therefore sexes) is to offer greater diversity of genes which help make a species healthier.

But if you added 3 or more sexes, then the process of sex becomes complicated, too complicated to make the extra diversity worthwhile.

Two sexes is a happy middle ground between diverse genes with not too much complication.