They're made up of DNA -- everything has it, we've got rats, we've got trees, we've got insects, we've got humans. And in the case of human chromosomes, geneticist Melissa Wilson: Typically, from your genetic mom and one copy of every chromosome, and we have 22 of these that you get one copy from mom. And then there's a 23rd pair, X and Y. Molly Webster: So while all one through 22, we do not call X and Y 23. I like to think that they are waiting. But in this instance, they were like, "We're just going to keep the letters, and then we'll give them a title." They called them the sex chromosomes. Now I would wager these are the most well-known chromosomes for one simple fact: that we say X equals "girl," that they are responsible for sex. And -- and I had to learn this -- but when I'm talking about "sex" here, I'm talking about the way biology which are our ovaries and our testes -- I'm not talking about gender. And so, as a reporter at the show -- "Radiolab," the audio documentary, I was like, what's up? You know, that's kind of my job, and then I get to call people about them and ask questions. And in this case. And in the two years I had as part of "Gonads," I ended up doing for "Radiolab," I found out that these two chromosomes a little unsettling; where things that I thought were facts were, like, twisted in ways. And the world goes so far. I was like, "Maybe we should all talk about this." So, you're you all, we're all going to talk about it. And for me, the true story of X and Y. So within years of being discovered, these two little chromosomes. There was diplosome and heterochromosome and idiochromosome, and most of the names had to do their size. And then there was "sex chromosome," which they had been given that we had started seeing that the X and the Y would often go with the males. But scientists were like, "Do we really want And science historian Sarah Richardson: "You should not call them The X and Y have many functions, and you wouldn't assume controls a single trait. Imagine calling one chromosome or the 'liver chromosome.'" MW: Scientists, if you dig, it's really cool. You should. Were hesitant to, like, and such a powerfully connotated name. There was a fear that it would maybe to science, maybe to society -- but the fear was in the room. And you can see they ended up it's like a pretty juicy title. It popularized genetics, you know? But in the 100-year history you can see it starts. So around 1960 -- this is going to be our first stop on the complicated world. So around 1960, we had discovered that you could be XYY. They discovered an XYY man. And to digress a little here, it turns out that the model is really simplistic. You can actually be a whole bunch giving you, like, different types. You could be two Xs and two Ys together. You could be four Xs. You could be XO. And so I thought that was pretty crazy, because I was like, "Wow, this really upends I think most of us in this room." So a few years after they realized, researchers go to a prison in Scotland, and they do genetic analysis. And they find a number. And according to Sarah: SR: They just rushed suggesting that this extra Y chromosome could explain criminality in some men. MW: Yeah. So the logic goes like this: By this point, we're thinking Y is male. We think male is aggressive, so Y must be aggression. If you've got an extra Y. And like, we went nuts with this theory. We called it the supermale. They started scanning more prisoners, serial killers, boys. And in all seriousness, there was actually a suggestion. So in 1980, this theory pretty much toppled. One, there had been this really large study that basically showed between Y and violence, I think we all saw that coming. And then, there was one other thing. SR: Going back in that high-security, they had also found with an extra X chromosome. So these are XXY, as opposed to XYY. MW: Really? SR: Yeah. That the individuals were superfemales. They never investigated. MW: Seems like kind of an oversight. I don't know. But I think it's interesting, because what you see is if you start through the lens of sex, what naturally falls in place behind is we look at them and the traits. So men were violent, and Y explained why they were in prison. The X did not do that, because like, you know, what's X? We don't associate it with violence. And while we don't believe God, I hope we don't -- we don't believe in supermales today, there is a very similar conversation around inherent violence. So my next stop or things feeling. The World University Games and the Spanish hurdler María José. She was like a hot shot. And the night before her race.