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Hank gets into why sex is the preferred method of reproduction for most species - and it's not for the reasons you're thinking.

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References for this episode can be found in the Google document here: http://dft.ba/-2ACF
Have you ever wondered why we have sex?

(Intro)

Okay, correction, have you ever wondered why there IS sex? I mean, I'm sure that your parents went over the basics with you when you were 11 or maybe you learned it from that like, bossy girl at the public swimming pool... But not matter where you learn it, the gist is probably the same - we have sex so that we can have more people. Same goes for grasshoppers and pandas and poppies.

Sexual reproduction exists to make new animals, right? But some animals totally abstain from sex, and they still get the job done, making babies all day long all by themselves. If it's possible for some animals to reproduce without having sex, why doesn't everybody just do it that way? You know that something's up when the majority of all animals reproduce sexually at least some of the time. Some biologists have calculated that 99% of plants, animals, fungi, and protists have sexual reproduction - at least some of the time. And some animals, like starfishes and slugs and strawberries - they can do either, depending on how they're feeling that day.

So, sexual reproduction: that just means that two organisms of the same species get together and combine their genetic material to create a new organism that's genetically a little bit different from both of them. Included in this category are: you and me, and all of the pandas and grasshoppers and poppies. Asexual reproduction doesn't rely on mixing anybody's genetic material. Basically, it lets you make a baby whenever you feel like it, creating a genetic clone of yourself. And this can happen in a number of different ways.

Binary fission, which a bunch of bacteria and protists and unicellular fungi do - this is when an organism just splits in half and the halves go about their business until they're mature enough to split in half again. Budding, which is what hydras do. They make little buds that pop off of the mom hydra when they get big enough.
Organisms can also produce vegetatively, through bulbs or tubers or rhizomes.

And now for parthenogenesis. This lil' girl here is a New Mexican whiptail lizard, and I know that she's a girl because they are all girls. Parthenogenesis literally means, "virgin birth." These whiptail lizard ladies can form embryos inside of themselves, without being fertilized by a male, which is good, because there are no males. It's more common in arthropods, but as larger animals go, lizards seem to have the knack of it.

There's also fragmentation, where a parent can break into a bunch of different pieces, each of which can then produce its own offspring and, I could go on and on.

So, on the surface of things, making these quick and easy copies of yourself seems to be a pretty good way to go. I mean, sex is awesome and everything, but it isn't particularly convenient. First, you have to find a suitable mate which - y'know, we've all had our troubles with. And then you're stuck with only half of your population being able to give birth, the other half just being useless. And generally, sexual reproduction happens on a slower time scale. By the time sexual reproduction results in one round of offspring, asexual reproduction has had, like, three generations and they're all off in the world making friends and influencing people.

And yet still, sex is a thing. It's a very popular thing. It turns out that combining the genes of two different members of the same species is worth all that time and effort. The key here is that gene variation makes a population of organisms less susceptible to disease, and more able to survive if conditions get crappy.

When times get tough, the population is genetically diverse enough that at least some members will survive. And, say a population is all but wiped out, sexual reproduction allows for a genetically diverse population to rebuilt from a relatively small number of individuals.

And then there is the Red Queen's Hypothesis, named after the red queen in Lewis Carroll's Through the Looking-Glass, who said, "It takes all the running you can do to keep in the same place." The idea here is that a species needs to constantly adapt in order to keep up with predators and parasites and competitors - studies have shown that snails and worms that reproduce sexually are way better at resisting infestations than snails and worms that reproduce asexually. It's basically an arms race, and sexual reproduction and the genetic variation that it provides is the only way to keep up.

And finally, possibly the best reason for sex is the same reason that we don't tend to mate with our family members - organisms that reproduce asexually rely on genetic mutations for all of the genetic variation within their population. But most of the time, when genes mutate, the result is a bad thing for the population. So after many generations of cloned organisms, the bad genetic mutations tend to pile up, and they can actually wipe out entire populations. Which is why lots of organisms that reproduce asexually when conditions are great, reserve the right to sometimes reproduce sexually, if conditions get worse.
So there you have it: asexual reproduction seems like a great idea, but in the end, sex rules.

For more information on sexual and asexual reproduction, see our citations in the description. If you have questions or suggestions, you can ask us on Facebook or Twitter, or of course, in the YouTube comments below.

Use a condom... or birth control... or both.