A lot of us understand biological sex with a pretty fateful underpinning: if you’re born with XX chromosomes, you’re female; if you’re born with XY chromosomes, you’re male. But it turns out, our relationship to the opposite sex is more complicated than we think.

And if you caught this show on-air, and would like to listen to the full version of our Sex Ed Live Show, you can check it out here

This episode was reported by Molly Webster, and produced by Matt Kielty. With scoring, original composition and mixing by Matt Kielty and Alex Overington. Additional production by Rachael Cusick, and editing by Pat Walters. The “Ballad of Daniel Webster” and “Gonads” was written, performed and produced by Majel Connery and Alex Overington.

Special thanks to Erica Todd, Andrew Sinclair, Robin Lovell-Badge, and Sarah S. Richardson. Plus, a big thank you to the musicians who gave us permission to use their work in this episode—composer Erik Friedlander, for "Frail as a Breeze, Part II," and musician Sam Prekop, whose work "A Geometric," from his album The Republic, is out on Thrill Jockey.

Radiolab is supported in part by Science Sandbox, a Simons Foundation initiative dedicated to engaging everyone with the process of science. And the Alfred P. Sloan Foundation, enhancing public understanding of science and technology in the modern world. More information about Sloan at


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00:00:00I am Robert krulwich Radiolab is supported by netsuite by Oracle the business management software that handles sales Finance accounting and HR in a simple Cloud platform get the free crushing the five barriers to growth guide at next week. Com radio app
00:00:20hi I'm Robert krulwich Radiolab is supported by ZipRecruiter hiring is challenging but there's one place you can go to make hiring simple and smart that place is ZipRecruiter we're growing businesses connect to qualified candidates try it for free but radio app ZipRecruiter the smartest way to hire
00:00:44wait you're listening to Radiolab
00:01:02gonads episode 3
00:01:05Emily Webster hello hello are you still there I'm still here and this is my mother Mary Webster but it's the end of the bed bugs are such a freaking pain get the vacuum all of the baseboards at the vacuum the floors yet to vacuum the door jambs to crawl up the walls and they're trying to get away from that sounds awful so I recently called my mom for I guess the catch up but also
00:01:35I had a weird question
00:01:41that's been bugging me
00:01:47what's on my mind so I asked her mom been working on the story and it made me wonder what you would have named me if I was a boy would have been named Daniel and if we ever had a boy dad said he was going to name him if that's what you want honey instead he got a Judy Chrissy Peggy and Molly for father Mike lucky father you would have been all of us at work no we went Daniel for a boy that's for everybody
00:02:41so this is just going to sound ridiculous but I called my mom because all the stories that we've been doing in the series
00:02:49they do make you think about fate
00:02:52like even if you think about the first one where they're the primordial germ cells and they're holding on to all sorts of possibilities and Futures and then
00:03:06chromosome step in no more Infinity you're just like shunted onto a pass
00:03:15I guess I I guess it I guess asking my mom about Daniel was just like a clumsy way of getting back to what feels like a really pristine Moment Like a moment where who decision had been made where you exist totally unblemish by life and choice in fate
00:03:38maybe life isn't so faithful
00:03:42case and point David dark hour I'm just going to do my name is is pronounce dark over my head I don't think my parents I pronounce up with that I like a V it's it's such a Polish that's good genetics cell biology and development that's that seems scary it's broad anyways the reason I called the dark over was because I came across the series of experiments that he did that just straight I've kicked me in the gonads okay so to begin this was back in the early 1990s is that cover was working a lab doing genetic stuff in worms and flies and and mice and things and Presto we got lucky he and his team discovered a brand new Gene
00:04:42what does its dmrt1 dmrt1 you're saying was that this Gene was in mice but also in humans and in the mail Mouse it was expressing itself in the testis
00:05:09can I say a testis testis testicles is that a single yep okay so yes we found this Gene and humans had it in the testis and the question we had was whether was doing something or not like you got jeans in your eyes that are making chemicals that are making your eyes the color they are Gene dmrt1 what is it doing we want to know if it's involved in maybe making sperm or maybe it just hangs around it doesn't matter doesn't do anything you know we don't know let's mess around with it and see what happens
00:05:43but you can't do that experimented humans know so instead they get some adult male mice normal fertile males are making sperm use some fancy molecular genetic tricks and so basically kind of mean trick but it's genetics and they look at it under the microscope and it didn't look like what we would have expected that help make sperm in the testis and normally they're kinda tall and lean long and skinny but suddenly there different with dmrt1 gone they have gotten smaller rounder and Zar cover was like Snot something is supposed to happen is going on here what are these things he realize that the cells are making estrogen and he was like
00:06:44I think what is happening is that the cells in the testes turned into ovary cells
00:06:51wait what and where is the male Mouse yes you're saying this male Mouse now has ovary cells and its testicles yes that's these are cells that are changing their sex
00:07:05that's insane can I come we just have like a exclamatory moment like where you where you like whoa is that pot that's possible that happened what is the you know if all scientific explanations is that weird I'm so we have that weird moment just to take this weirdness like one step further a group of scientists did similar experiment in adult female mice where they did like the same as a female Gene in the ovary and when they went to look at it over is trying to kind of reorganize itself into a testis weight
00:07:49you sing in both cases there is one gene it's flipping the sex from male to female and back yes one gene one gene how many teeth do we have in our body I don't know like tens of thousands just one is doing this which is
00:08:06weird concept to think of because we typically connect like sex or gonads to chromosomes at least I do like an X and A Y right girl and a boy so how could Gene Steffy and reverse that cuz I thought from a lots of genes are these like massive things when she is so tiny tiny chromosomes are much bigger and I think the answer to that is that when you get down to sex like what makes us one sex or the other it's not it doesn't work exactly like we thought I take for example the X & Y idea this like
00:08:42chromosomal narrative we have a biological sex it's a specific way of thinking about things from a certain moment in history that we are
00:08:53actually starting to rethink I think it's helpful to see sort of the the history of how we understand sex and in a in a longer time frame so let me bring in this guy David page biology professor at MIT where do we start oh my gosh well we're going to go so we'll see we could go off the rails and any number of directions here all it's all over to be quite a productive but let's see so let's go back to the 1890s
00:09:25yeah that definitely is 1890s so so genetics was in its infancy Mendel Keys all that was happening or where do boys and girls come from Mom and Dad clearly involves the children ended up growing up looking something like their mother and their father I can maybe you have a chin like your dad and nose like your mom and a hair that's a little bit of both there was a kind of blending of mom and dad to make you you
00:10:02when it came to why you were the sex you were that was a mystery because there was no funding either your mother or your one or the other girl for it must not have anything to do with heredity it had to be imposed from the outside and some way so people came up with all kinds of ideas for what made you a boy or girl moment of conception cold Dark Moon definitely a girl everything that was bad was given to women are there was what the mother ate mom's body heat stress
00:10:501923 we started looking elsewhere but how do we inherit our characteristics for an answer on our physical appearance and our sex scientist looking down the barrel of a microscope discovers to new chromosomes but I just want to hit pause here okay I came to find out for actually from David page that the X and Y chromosomes do not look like an X & Y where they don't look like the letters and they first discovered them under the microscope they just look like these misshapen clumps but that's it that's so interesting because there's something about the shape of the X in the shape of the Y which read it as gendered letters that feels so yeah
00:11:50quality or something in the acts which feels like you know ovaries and breasts or something like there is like there is something about those letter so I was totally shocked when he was like there's no real reason they got those letters it was totally arbitrary anyways when they found these chromosomes female and if you had a y chromosome XY you develop is an anatomic mail that's right that was the thinking
00:12:28but then that idea I got more complicated when did you intersect with this story summer of 1970 and the TNA Revolution he was involved in what he described as like the precursor to the Human Genome Project what would become Human Genome Project working with the group of senior scientist who work envisioning maps of the human genome exceptional human individuals who had not been understood previously
00:13:28like most men women usually have a pair of exits and they're also looking at men appear to be those two Google of a female x x + 4 Page and other scientist they're like oh there must be something more Happening Here than just like the chromosome there must be something deeper going on here the trail now of the secret scientist across the world start looking at these people's chromosomes do females wear actually missing a little bit of the Y chromosome wasn't there females were missing was the same bit that was present in the XX males a little bit
00:14:28excess of these XX males clear that this must be the bit that matters
00:14:37and around 1999 to say they've made a major Discovery scientists in Britain announced Aid found this one gene on the y-chromosome the genetic trigger on the Y chromosome that determines whether a baby will be a boy or a girl what they found is that of the 200 genes on the Y chromosome there was this one single Gene that acted as the switch the master switch the grand master switch. X & Y as a whole it's one tiny piece
00:15:22so back in the first episode there were those primordial germ cells and they had to go on that super long journey to get to the gonad Cathedral and on the journey when I got to the cathedral they were full of potential I think of the anything in the mail they coming female that could be whatever your version of anything is and then when they get there there's a moment where like we said fate stepped in and just like swept all their possibility away and said you are one thing and this is the thing you will be missed Gene is fate this Gene the scientist discovered if it shows up then you shoot off down the path that is sperm testis mail and if it doesn't show up you shoot down the path of egg over easy female and the scientists gave this thing and a name sry
00:16:22it is like sorry
00:16:27like your man song
00:16:31so it sounds like we've gone from like crazy ideas about what makes a boy or a girl to chromosomes to now like
00:16:38this little Jean yeah but the the sry gene that you just mentioned is different than the gene that I just heard about from free anything's are cover his brothers are cover yes it is I think there's a difference. The same gene or is it dmrt1 is it different Gene and sry but this this is what's so crazy about the MRT want okay primordial germ cells there in the embryo there waiting to become something
00:17:07and then sorry shows up but just comes on for about a day and then it goes away but once it turns on it then starts this like Cascade of Gina Regina after Gene that all sort of say your mail your mail your mail and what all of these genes do is they create chemicals that send out signals that start forming and shaping the testis and as soon as the test is begins to develop
00:17:38on turns 4th gdm-41 zarkovich Gene is important for finishing the job of making a testis but it doesn't go away at that point it stays active
00:17:57in the womb when the testis is just growing and then when you're bored and through you know childhood your teenage years adulthood like until you die dmrt1 is on and if you take it away like Sark overdid the cell will actually change sex which leads you to believe that damn RT one is actually preventing a cell from switching Sexes that's right so I called Glen Capel who is a geneticist from our first episode and she explained that what all this means is that that other past the past it you did not take in the gonad Cathedral it never went away it's actually still there you you carry it with you always it's just that that Gene has been shaking it yeah way timer pressing the other path way my whole life like I think we think so yeah really yeah there's like a parallel universe male Molly
00:18:57yes I think there is there's a parallel universe male ball I just wait when you say this Gene has been shutting the other Molly was that even mean okay so you can think of it like this the code for that other Molly who I'll call Daniel that code is still in my cells and dark over says it what does Gene does is it sort of one of the things change as a sort of patrols and make sure that Daniel jeans don't turn on jeans been doing it turns out as playing whack-a-mole and it does maybe every day it's like an election that's always being kind of challenged that's where why cast the deciding vote and mail happened but there's a recount every now and then and if you Marcie one's not there to say nope still mail then you can go the other way so now I understand why you're so obsessed with Daniel because
00:19:57he's like trying to get out and it does go both ways like like if you know there's sry and there's dmrt1 but they have found these key genes in ovaries that you can turn on and off and have some more results why would our bodies be set up this way like you think once a decision gets made
00:20:18that you just make that decision and be done with it why would there always be the possibility of fun making the decision that is a good question and I will answer that after break
00:20:30but first i'm going to call my sisters
00:21:22this is Kayla Caldwell calling from Sunny Austin Texas Radiolab presents gonads gonads is supported in part by science sandbox assignments Foundation initiative dedicated to engaging everyone with the process of science additional support for Radiolab is provided by the Alfred P Sloan Foundation hi I'm Tracy and I'm a reporter here at Radiolab I wanted to take a quick second to tell you about something that I think is pretty cool that we make here at the show besides the show we have a newsletter and I can already hear you say big deal everybody has a newsletter but ours is really really good and worth your time and probably more worth your time than other people's newsletters so here it is first of all it lets you know when a release a new app
00:22:13and secondly this is whole other section of our staff picks and that's a list of things that the radio Latina come across that we're just really excited about and it could be something like it out Rachel keeps a car producer you know she just worked on gonads and she found out about this really cool Frozen zoo and then there's our other piece right and she kind of told everybody to Google Hearts mustaches and it is definitely worth your time to Google that so go do that right now or it'll be me talking about you know the joys are rewatching like my favorite TV show Living Single so I hope you'll sign up it takes about 30 seconds and it's free so go to backslash newsletter or you can text or L news as in a Radiolab news to 70101 that's RL news to 70101 and thanks
00:23:10hi I'm Robert krulwich Radiolab is supported by ZipRecruiter hiring used to be hard multiple job side stacks of resumes but today hiring can be easy with ZipRecruiter ZipRecruiter scams thousands of resumes to find people with the right experience invites them to apply to your job it's so affective that 80% of employers who post on ZipRecruiter get a quality candidate through the site would in the first day right now listings can try ZipRecruiter for free at this exclusive web address and zip radio app that's radio app
00:23:53all right back to gonads I'm Ali Webster everyone say their name or hello I'm Grace and these are my sisters Judy Chrissy and Peggy okay so so I'm going to tell you guys the thing that big of a deal but it's just sort of funny you're pregnant I'm not pregnant I'm not no no I just want to tell you about some reporting that I've been doing and then a funny thing that Mom and Dad told me that's all we ever know
00:24:33it's Chrissy this is ridiculous is basically about how we all carry in us like the opposite self that we never became so so I called Mom cuz I was like what would male Molly have been like like that you guys have like a name for male Molly and they were like oh we would have called you Daniel please reveal it's not Daniel Webster
00:25:15Jesus Mali man are you surprised that your name would have been Daniel Webster that you would have been a Daniel Hall no I didn't know that I don't feel like my inner Daniel Webster would have that much of a different life than I have but I think you guys honestly this conversation but I think you guys walked out because I was the one that was raised with the Hoops that there was like some Daniel lingering in me isn't Daniel Webster like I took a picture of a statue of him once and send it to dad because I was supposed to be the annual who is Daniel Webster and was the under Secretary of State under three presidents will someone Googled fast or regular like old white lawyer dude
00:26:15Thor ages for douchebag it's all been worth it all right that's all that's all I got I love you guys goodbye
00:26:38you're amazing I'm sorry about your bed bugs bite
00:26:46okay so to catch everybody up we have learned that we are all carrying around with us another path we all have our own inner Daniel Webster's constantly stretching it for them whatever so my question for zark over was like why would I carry this path with me if I'm always turnt like if if I'm just turning it off do you have any answer I wish I had the answer so we don't really have an answer it could be as boring as well it doesn't really matter because normally no like a Genesis comes in Hacksaw Jim Archie one or turns on Fox L2 or whatever I'm so why solve a problem you haven't created that that's
00:27:29quite possible but boring the more interesting answer is that this is an evolutionary holdover from from a common ancestor with fish
00:27:42okay so this ancestor would be our great-grandparents 16 times removed which means 400 million years ago a fish swim out of the depths of the ocean crawled onto land and took like squelching steps forward and boredom boredom boredom poured through millions of years luck and chance and stayed until finally getting to
00:28:10you and me
00:28:12and boo hello hello can you hear me yes can you hear me so sure can my name is Bob Warner I'm research Professor studies Evolution and Marine Biology UC Santa Barbara what's your traction to the ocean the whole idea that there is a different world under there
00:28:35well I'm just going to happen brother out of this so down in the waters around the Florida Keys there swims a remarkable fish it is a very common coral reef fish this is Marshall Phillips graduate student at North Carolina State University like Bob said he's blue heads yes anyways down and the keys are some Primo spot nice patches of reef blue head
00:29:07in that group there will be a single large brightly colored male with a blue head and a shiny blue green body and it has white and black stripes right behind its head that go black white black that we very technically called the Oreo and if he's got a big Oreo well that's a sexy male
00:29:32and then the rest of the group is essentially a harem of Lady Fish in the group are little and yellow pretty and kind of swim a little slower watching out for thing where the mail is flashing 13 all around much more aggressive and said this one male and a female entire lives on this one patch of where they make everyday female with that one male and Tails is the male and the female will Dartmouth in the water column together and then at the same time he'll release his sperm and Show release exponente dark right back down and then a different female same mail go up eggs sperm and dirt back down and then again different female same mail they go up then this is what they do every day over and over sounds like a call to the 1960s but say something happens to this mail will say a predator comes along
00:30:32any Trump's that mail so the alpha male dead gone
00:30:39now the question is what happens to the ladies you think it would be chaos because their whole systems been thrown out of whack but within minutes to hours life finds a way
00:30:55somehow the ladies pick who will be the next mail but somehow they figured out until Wednesday stablished who the largest email is she starts to change her behavior she gets a little more friendly towards the other females just went up to them do this little weekly dance started waving her pectoral fin at the ladies which isn't really something they do as a female ever and then as time goes on her body starts to change she will get a little bit bigger
00:31:40how do you just suddenly get bigger testosterone or brain start sending signals to produce tons of testosterone testosterone is is taking over and a she starts to grow a little bit of blue start Superior right adornos her scale start to change color then sort of spread backwards right at her chin and spread out words until her head is entirely blue and then these darkstripe start to form those will eventually become that black white black Oreo and the other thing that starts to happen is her ovaries start to disintegrate
00:32:17these are the most valuable cells in the body and now suddenly they're being destroyed that start producing sperm really rapidly it it's not it's absolutely incredible
00:32:35and then
00:32:37sex called is back new dominant male at the top of the heat but at first he's not very good at being a male like he doesn't quite know when to Dart up and went to spawn it's just like a teenager who doesn't know how to talk to girls but eventually you'll get the hang of it and then produce baby blue heads and the cycle of Life continues is it good Adam bro thank you as crazy that they just disintegrate their insides and then rebuild but the funny thing is if you ask Bob about this stuff in fact about how these little lady fish completely transform he's like how many
00:33:25fishes change sex
00:33:29it turns out it's a lot of fishes nearly all the Russ's you blue had your fairies or flashers parrotfishes the tiny gobies damselfishes everyone asked about clown fish Finding Nemo yes they change sex but made it a little differently there go from male to female jockey dealing with like hundreds
00:34:00here's a really crazy thing
00:34:04it's not just fishes some shrimps worms alligators if you include all of the animals in which their sex goes a different way than you would think laws Lobster's bananas lizards or Birds muscle snails slugs chickens chickens eat frogs it's just amazing and wait till we get to Turtles
00:34:23it's a whole zoo in this conversation so why would fish like why would why would any animal change Sexes exchange increases your Fitness you have more young either eggs you produce or exit you fertilize then you would as a as a single-sex your genetic material like a beer the fishes on the reef and the mail disappears near stuck and there's no there's your DNA goes nowhere but if you can become a male you can make sure that your DNA go somewhere and then like all the other fishes in your little kingdom go somewhere else for the next obvious question you've told me that we come from the fish they've got this flexi sexy thing and the we have it to some degree Daniel lurks within you and is being actively suppressed every single day
00:35:20so can we be like the fish yeah it does make you think of that zarco verse says that ever since he did those mouth experiments he gets his question a lot of this could be something to be helpful but we can't do it at 3 technically can't possible to take that Gene away and even if we could removing a gene just won't physically reorganize Us in the way the fish do and he says that most you might be able to produce your own natural sex hormones of the type that's more aligned with your gender identity to do that but the reason we can't actually do the full on switch is because humans are male and female humans have developed internal reproductive Plumbing that is so different from each other it would be impossible to drop of a hat
00:36:20to switch was it then then this this makes me confused well is this to use blank to the word from a few episodes ago as is by potentiality that still is there latent being suppressed is that a legacy thing that it's just fading away or is there is it there for a reason it's there for reason in the fish is it there for a reason and does it serve a purpose and therefore will be that with us always always a good answer for that
00:36:58but it do you think anyone does or it's just like a
00:37:05no I don't think anyone does I think we're all trying to figure out why it would be the case and most people ask the same question you asked me why would this be true and I don't know why would be true even if we don't know why just knowing that that other path is there just below the surface you know wanting to express itself does make you think a different way about how rigidly we Define ourselves
00:37:38I think we like to bend people as male or female and we both always put people into piles but I think there's a tremendous amount of Middle Ground
00:37:49even when you're just talking about you know things like the level of testosterone you're making or the level of estrogen you're making or the shape of your genitalia or many other features that we we we been as male or female I think there is a lot of there's a lot of variation between the two piles
00:38:11and maybe we just haven't appreciated the variation that exist naturally in our population
00:39:13how are you Kevin
00:39:58this episode is reported by me Miley Webster and produced by Matt kilty with additional production helped by Rachel Cusick that Walters was our editor scoring mixing an original music by Alex overington and that kill the gonads theme and The Ballad of Daniel Webster were written performed and produced by Major Connery and Alex overing 10 special things for this episode go to Erica Todd Anderson Claire Robin level badge and Sarah Richardson thank you to composer Erik friedlander for allowing us to use his work Freya was a breeze part 2 and musician Sam prekop who's work a geometric from his album The Republic is out on thrill jockey I think you should sign up for the Radiolab newsletter you might think his newsletter what's the big deal everyone's got one but in our newsletter you're going to get a bunch of Staff picks telling you about super cool things we discovered while reporting this Siri sign up at newsletter or text gonads 2701 - 0
00:40:57Radiolab presents gonads is Rachel Cusick Pat Walters Jad album Rod and me Miley Webster see you next time
00:41:06hi it's not you. Calling from Newcastle California Radiolab was created by Jad album Rod and is produced by swine wheeler Dylan Keith is our director of sound design Ram at Sr Padilla is are managing director our staff includes I'm an Adler Mighty bartolomeo Back of wrestler Rachel kusick David Gibble Bethel have tea Tracy hunt Matt kiltie Robert krulwich any McEwen Latif Nasser Melissa O'Donnell Aryan whack Pat Walters and Molly Webster without from Shima or Lele pons and Lisa Yeager are fact Checker is Michelle O'Hara

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