 Here's the bottom line. Genetic diversity makes you more capable of fighting parasites. Now, genetic diversity has advantages in populations because it makes them more likely to be able to deal with whatever crap comes up if the environment changes. Genetically diverse population is more likely to have individuals in the population that can adapt to the environment effectively and handle the new challenges more effectively, and then the population is more likely to continue on. So there's definitely benefit for genetic diversity just in general, but they've done some really interesting research that indicates that genetic diversity specifically helps in the battle against parasites because parasites are extremely common and thoroughly disgusting and utterly fascinating, and we're like in this arms race with these parasites. They want to destroy us. They want to live with us. They don't want to kill us, but they basically want to eat all our food and have us just serve them, and meanwhile, we get weaker when we have parasites and we aren't nearly as pretty when we have parasites, and so we don't like having them. So it's kind of this little arms race. The more genetically diverse you are in a population, the more likely you are to be able to battle the parasites. So they've done some really interesting studies, and I want to show these, I want to give you some examples. For example, they have a snail in New Zealand. I'm going to draw you a picture of this lake. And the way that this little situation works, there are snails that can be infected by flukes. The snails are the host and flukes are the parasite. Now, what they found is that there are fewer parasites, there are low parasites in the streams. Low parasites, got it, and there are more parasites in the lakes, more parasites. Now, snails can be male or female, and they can actually switch male or that's female or male. And what they found is in the high parasite places, there are more male snails, and in the low parasite places, there are more female snails. Now, why? What's going on here? Well, think about this for a second. Male snails, what is the point of a male snail? The only point is to deliver sperm for sexual reproduction. Sorry, fellas, snails. I think you're cool and everything, but that's it. Like, lady snails can reproduce asexually, they just make their eggs so that they can grow on their own, that male snails are there basically to deliver sperm. In areas that there are lots of parasites, there is lots of sex, possible. In areas where there's fewer parasites, why spend the energy on sex? Let's go asexual, we have a choice, we can. We might as well avoid the whole energetically expensive sex thing anyway, we can make way more babies way faster and just do it ourselves, and we can get away with it because there's fewer parasites in the stream. What? How cool is that? They've tested it further. They found that ducks live near the shores and carry their part of the fluke life cycle, and they found more snail, more boy snails closer to the shores than out in the middle where there were fewer parasites compared to the shores. They've done lots of research that has indicated that, yeah, there actually is this link. Now, that's one thing, to show that when we're exposed to parasites, we're more likely to make babies. The next question is, is it true that... Lady-anythings find parasite-free fellas more attractive. So is it true that your genetic diversity that makes you parasite-free actually does make you more attractive, is it parasite-related? Let's look at who is sexy.