Questions about genders ... male/female

[bennyboy]

Greetings!

I'm new here, so I'll add a short reason why I am asking this question on this forum.

I teach worldviews classes to high schoolers. We cover Secularism, Postmodernism, Islam, New Spirituality, Christianity and Marxism. Within each worldview we cover each discipline of theology, philosophy, history, economics, sociology, ethics, biology, psychology, law and politics and how they differ across the board.

We are currently in the biology unit ... and I've pondered this question from an atheistic evolutionary viewpoint for a bit ... and I can't seem to find an answer.

So, I thought I would post here to see if you all could offer some insight.

Why do we only have two genders, male and female? [excluding asexual animal reproduction] ... just humans and almost all animals? Why only two? Why not ... say ... seven, or seven-thousand? If we have evolved over time from a single celled organism ... why did we only evolve into two genders and not more? Why did it stop at two? Thanks for your time.

Well, you have the innie and the outie-- and then you run out of plug-in options.

I think the idea of a multiple inheritance through shared DNA is pretty cool. Maybe people will do it eventually, artificially.

We have a good narrative for sexual reproduction-- it provides a mechanism for variation, allowing a better chance for at least some individuals to survive a change in environment.

But what would a third genetic source do? More variation? I don't think so-- it would be simpler to ingrain variability in 2-party reproduction.