 Hi, guys. We're back for the epic and glorious lecture of all times on my two all-time favorite topics ever. Sex, which is an incredibly fascinating and utterly bizarre phenomena, and parasites, which are quite possibly the coolest thing on the planet. I apologize in advance for effectively linking sex and parasites in your brain, but I'm going to make a case that they are actually very tightly linked. We're going to start out by reviewing, like, why are we talking about sex in this general biology course? And I have a reason. I think, you know, this is actually a really good time to talk about sex because we've just spent an entire unit talking about cellular reproduction, like, how do cells make copies of themselves, and genetics, heredity, how do we pass our information onto our children and what are our children going to look like? So really, you know, we come back to this image that we dealt with in the very beginning of this session, and it was the human life cycle. Like, why? Why are we here talking about the human life cycle? Why are we looking at it again in this lecture? And it's because we are focusing in rat her. This process right here, essentially, sex is a, what? An act that joins two gametes. And there's a whole bunch of different ways to do it, and in the animal world and in the plant world, oh my gosh, all the different ways that critters have come up with to basically engage in sexual reproduction, to carry out the task of joining sperm and eggs. It's fascinating. Take zoology if you want to learn about animal sex because that's basically what the entire class is. Because that's kind of like why all life exists. You could argue that everything we do is geared basically toward passing on our DNA and making babies, which is kind of wild. Sex is a huge part of that, obviously. So the first thing that we're going to look at is a realistic evaluation of the costs of sexual reproduction. And I have some stories to illustrate that, dude, it is so freaking expensive. So there has to be some benefit. Like, otherwise, why would we do it? So we're going to talk a little bit about the benefits and then make the link to parasites and then take a little, like, wander down the parasitic runway because parasites are so awesome. So we have to talk about some of them because they're so cool. All right, so first of all, go ahead and think in your brain, like, what are some of the costs of sex that you can think of? And then I will come back and I will make my case for some of the costs of sexual reproduction.