IRA FLATOW: Now, if you want to dial back on the way back machine to this next one, I want you to think back to school, right. You’re sitting in the sex ed class, health class, maybe for some of you, where movies like this one may have been the soundtrack.

SPEAKER 1: The spermatozoa shed by the male during mating appear like tiny little fish or shall we say tadpoles, very active squirming fellows. Notice the large head, the lashing, whip-like tail, and the streamline effect, in general. These organisms are built for speed.

IRA FLATOW: Yeah, I remember that one and then the next lesson, chromosomes, right, your x and your y, the formation of an embryo. You got to terms like germ cells and gonads. Well, well, it was that word gonads and a researcher who referred to them as magical organs that sent Radiolab producer and host Molly Webster on a mission, a quest to spark our fascination with human development, x and y embryos, and her new limited run series.

It’s out now. It’s called Radiolab Gonads. Welcome back to Science Friday. Good to talk to you again.

MOLLY WEBSTER: Hey, Ira, how are you?

IRA FLATOW: You were once an intern on our show. You’ve gone so far.

MOLLY WEBSTER: I was. I was. Yes. I was thinking, oh, this is what it was like when I sat up all their guests.

IRA FLATOW: You are now one of them. It’s a life imitating art.

MOLLY WEBSTER: Oh, yeah.

IRA FLATOW: Let’s talk about a few years back. You reported a story on surrogacy– donated wombs and sperm. And that sort of ignited this curiosity for you?

MOLLY WEBSTER: Yeah, it was a story about a sort of international surrogacy, like how folks were trying to create families across borders. So it was a same-sex male couple got eggs and then got surrogate women in India, who then moved to Nepal and created a family.

And in the middle of reporting that story, I realized, wow, there is a lot going on with how we think about families and how we understand just simple questions like, what is a mother, or who is a parent, or what is a sibling? It felt like there were a lot of like open-ended definitions all of a sudden. And science was changing so much at that time that it felt like an interesting world to stand in.

IRA FLATOW: Yeah. Well, let’s talk about speaking of interesting. The first episode of this series you ask a bunch of people– you do– a bunch of people on the street, what does the word gonads mean to you? And all these people we hear on this bit of tape say, testicles, like gonads has become the slang term for men. And I want to play a clip of that vox pop, because then you ask them this.

MOLLY WEBSTER: Did you know that ladies actually have gonads also? The gonads are both testes and ovaries.

SPEAKER 2: Oh, really.

MOLLY WEBSTER: That it’s actually for men and women.

SPEAKER 3: Really.

SPEAKER 4: I did not know that.

SPEAKER 5: I did not know that.

SPEAKER 6: Did not know that.

MOLLY WEBSTER: 90% of the people I talked to–

SPEAKER 7: Didn’t know that.

MOLLY WEBSTER: –they didn’t know it.

SPEAKER 8: Who would have thought women and men both have gonads.

MOLLY WEBSTER: Culture– they’ve stolen the word and made it male. And I think it’s time we reclaim this word, like as a citizen, as a human, as a lady, as a science lover. I’m taking the word back.

IRA FLATOW: And that’s what you did.

MOLLY WEBSTER: Well, I am trying do, Ira.

IRA FLATOW: So what is the term gonad then actually mean?

MOLLY WEBSTER: Yeah, so gonad is actually a very serious science term that researchers don’t giggle at when you talk to them about it. It means sort of two things in this interesting way. One, it’s just ovaries or testes. So men have them and women have them. They also use the term gonad when talking about very, very, very early in development before you have developed either ovary or testes, when you’re sort of like a bi-potential creature and gonads are just starting to develop.

IRA FLATOW: I’m Ira Flatow, and this is Science Friday from WNYC Studios. Speaking of WNYC, we’re talking about gonads with Molly Webster, who is also a producer and host of Radiolab. So your adventure– and this adventure is a great segment of Radiolab– you talk about the journey of the gonads early on. Tell us about that.

MOLLY WEBSTER: Yeah, yeah. So it’s– the gonads sort of develop in two parts. You have the actual what I call the house of gonad, which is that the testis or the ovary. And that is developing sort of in the center of the embryo. But then you have this other part that is the primordial germ cells, which are these cells that will ultimately become egg or sperm, right.

They’re the cells that are required for like the survival of the species. And those cells don’t actually start in the embryo. They start out in what we call and what scientists refer to as like the trash bin of the embryo, which is the place where the actual developing body of an embryo is then connected to the placenta and uterus. And so what ends up having to happen is those primordial germ cells need to get to their final resting place, right, which is going to be the organ. And so they go on this week’s long sort of migration journey against all odds through an embryo that’s trying to make them become liver cells, and heart cells, and lung cells, and they try and like eyes on the prize get to the gonad.

IRA FLATOW: That’s great. And you have a–

MOLLY WEBSTER: We’re going to make a whole line of T-shirts. I have a lot of gonads slogans at this point.

IRA FLATOW: Well, maybe you can put the X’s and Y’s on there too, because I know you have a new episode coming out this weekend that questions the idea we were all taught in school, which is XX means girl and XY means boy.

MOLLY WEBSTER: Yeah. It’s interesting. And one of the things I found out about it when I was looking into this is, one– that is actually not right– and you have– there are many instances where XX will lead to a boy and XY will lead to a female. And the reason behind that is because it’s not so much chromosomes that give us biological sex but genes.

In fact, one very individual important gene called SRY that was discovered in the like 1989, 1990. And it is actually this gene that as it floats around and attaches to different chromosomes will drive production towards male. And if you don’t have that gene, you will go generally down a female path.

IRA FLATOW: So the chromosome is sort of just like a boat for the gene to hide in or be transported in.

MOLLY WEBSTER: Yeah, it interesting. One of the things I found out is there’s actually a lot of different genes that are involved in sex. And they’re not all located on X’s and Y’s. They could be on– I’m making this up– but like chromosome 17. It’s spread out throughout your DNA.

IRA FLATOW: Wow. OK, well, I’m glad we wound up talking about sex on Friday afternoon.

MOLLY WEBSTER: Yeah. I know you’ve been waiting for years.

IRA FLATOW: It’s good to have you back, Molly. Molly Webster is a producer and host of Radiolab. And that episode will be this weekend, coming up this weekend?

MOLLY WEBSTER: Yes. Yeah, yeah, yeah. We’re hoping to get it out for folks on Saturday.

IRA FLATOW: OK. Thank you for taking time to join us, Molly. Good luck with the show.

MOLLY WEBSTER: Yeah. Thanks so much, Ira.

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