Why Do We Have Sex? The Evolution of Sex in Humans & Animals.
Cannibalism genetics, disease, and evolution: the science of why we evolved to have sex.
Sex is strange.
Seriously, stop and think about it. Why do we spend so much time and energy finding someone whose body looks slightly different from our own to rub two of our body parts together for a few minutes to produce a baby nine months later?
There’s risk involved. It takes a lot of energy. Your blood pressure and heart rate skyrocket. You make unflattering faces as if you were anguished. And you have to spend a lot of awkward time getting to know someone else. Yet, it’s one of the most beautiful and pleasurable experiences imaginable.
For most people, the question ends there. Sex is pleasurable. It’s natural. Other animals do it. Therefore, we do it.
But why is that?
And what about the fact that most organisms are probably asexual? I say probably because it’s impossible to count the total number of bacteria and other tiny critters on Earth.
We’re always forgetting about microorganisms, aren’t we?
When we expand our field of vision beyond just what we can see, the picture starts to look a little different. Most animals don’t have sexes or sex. Most species have only females—no males—and they make exact copies of themselves en masse.
So how did sex evolve? And why do we still have it?
Let’s dive into the weird, murky world of sex and the sexes and see what we can find, shall we?
Close your eyes for a minute and imagine a fictional world even weirder than the one we live in. Imagine a world where sex didn’t exist. Imagine a world where you and everyone else were genetically identical. Everyone looked the same, everyone sounded the same, everyone thought the same.
Imagine a world where all you had to do was masturbate, and you could produce offspring. No dates. No Tinder. No headaches.
Sounds paradoxically wonderful and dystopian at the same time.
But on the bright side, every so often, someone would be born with a genetic deformity. They wouldn’t be an *exact* copy of their parents. They’d have blue eyes while everyone else had hazel eyes.
This is evolution at work. It’s also painfully slow.
But there’s a twist…
At some point, you discover that you can change your genetics simply by eating one of your dead friends. You were born with blue eyes, you’ve always wanted green eyes, and when your friend with green eyes dies, you can just eat them and, like magic, suddenly, you have green eyes.
Turns out, this fictional world isn’t so fictional, after all.
See that image of a creature above? That’s the bdelloid rotifer, a tiny, asexual microorganism that’s totally freaky. They live in ponds and other bodies of water, from Antarctica to your bathroom sink.
You can boil them or freeze them in minus-272-degree water, and they won’t die.
These tiny vermin are all female, and they reproduce asexually. They float around, eat bacteria (and their dead friends), and have babies.
Instead of sex, they use cannibalism to drive their genetic mutation. They absorb the genes they need, so they don’t have to wait for random birth defects to show up to make life interesting. It’s how they keep everyone from being the same. And the process by which they do it can help illuminate a major reason we do it, too.