Animal IQ

Why Don't More Animals Reproduce Asexually?

So we all know that evolution happens because DNA mutates when animals reproduce, and one of the main ways that reproduction happens is when genes mingle through sexual reproduction. But if that's true, then how did sexual reproduction evolve in the first place? If you know us, you know that chicken and the egg problems are our bread and butter.

Doing It Cambrian Style

In 2015, researchers from Cambridge University announced that they had discovered the oldest known example of a sexually reproducing organism. Fractofusus lived 565 million years ago, was neither a plant nor an animal, and would have been able to reproduce in two ways: first, spreading asexually from chunks that break off, and second, by launching packets of genetic material to hopefully run into something compatible.

Of course, there's no way to say that Fractofusus was the very first organism to get fract-y, but it suggests how the very first animals might have done it. After all, plenty of animals can reproduce asexually, whether primarily or only in a pinch. And early takes on sexual reproduction were probably more like how Fractofusus operated than the intimate affair that's all the rage these days.

Even today, many fish reproduce by spawning, where fertilization occurs outside of the body, but the earliest known example of sex itself also went down underwater. Microbrachius dicki lived in a Scottish lake 385 million years ago, and researchers have been able to identify the very first sexual organs. But believe it or not, these are not likely to be our ancestors — sex evolved several times in the history of life.

Green Algae

Dancing With Myself

So maybe we do have a pretty decent picture of how sexual reproduction got started — but that doesn't answer why it's become so universal. Like we said, asexual reproduction is still around, and even relatively complex animals such as boa constrictors and hammerhead sharks have demonstrated the ability to pull it off under certain circumstances.

Asexual reproduction has a lot of advantages. For one thing, you don't have to find a mate. If you ever feel lonely, you can just pop off a couple of clones and ensure your genes will survive for yet another day. Plus, you get to pass on 100 percent of your genes, whereas sexual reproduction only propagates half of each partner's genes. So what makes sex better than not-sex (besides the, er, obvious reasons)?

One idea is the Red Queen Hypothesis. In "Through the Looking Glass," Alice and the Red Queen race on a surreal chessboard that keeps them in the same place no matter how fast they run. And the idea is the same thing is happening with evolution. From predators to prey to parasites, all animals live in a state of equilibrium, but only because they're constantly evolving to get the better of each other. Sex allows for much faster changes than asexual reproduction does, and so when organisms aren't able to mix and mingle, they might end up getting left behind.

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Learn more about mating in "The Evolution of Beauty: How Darwin's Forgotten Theory of Mate Choice Shapes the Animal World - and Us" by Richard O. Prum, named a best book of the year by The New York Times Book Review, Smithsonian, and The Wall Street Journal. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Written by Reuben Westmaas September 21, 2017

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