Let's talk about heredity. Here's our 2018 chat with acclaimed science writer Carl Zimmer about his book “She Has Her Mother's Laugh: The Powers, Perversions, and Potential of Heredity.”
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Welcome to Stuff to Blow your Mind from how Stuff Works dot com. Hey you welcome to Stuff to Blow your Mind. My name is Robert Lamb and I'm Joe McCormick. And boy do we have a treat for you today. That's right, we're we're chatting with Carl Zimmer about his new book, She Has Her Mother's Laugh, The Powers, Perversions and Potential of Heredity. This is a fantastic book. I I was trying to finish it before we talked to him today, and I was up till two am last night and getting to the very last page. But it was worth it. It is a great book. I really highly recommended. It's a brick that's just full of weird, interesting delights and insights about how our views of heredity have changed over the years, all of the good and all of the evil that that knowledge has been used for, and uh and also where it's going in the future. Yeah. Yeah, this it's a fascinating book. I also I got to see him in conversation with the Maria Knakova at World Science Festival this year, in which he talked about the themes in the book as well, so it was a real It's a real delight to have him here on the show. And if you want to check out She Has Her Mother's Laugh. It is available in hardback, digital and as an audio book. So, uh, we hope you enjoy our interview with him, but certainly go check out his book as well for just an in depth, riveting journey through heredity. Now, wait a minute, we should say who he is. I don't think we've done that if you're if you're not familiar with Carl Zimmer and Carl Carl Zimmer is a prolific, excellent science writer. He writes for the New York Times. I think I've also seen these articles in the Atlantic and National Geographic all over the place. Uh. He's written a lot about parasites and uh, some of the most interesting stuff in biology is is Karl's territory. And uh and I really had a good time talking to him today. Yeah. Some of his past books include Parasite, rex Evolution, The Triumph of an Idea, and Microcosm. So, without other ado, here's our conversation with Carl Zimmer. So, Carl, what led you to write a book about heredity? I guess in a way, I've been thinking about heredity for forever. Really. I mean, I when I was a kid, you know, I would uh think back on my ancestors that my parents told me about, and you know, I wonder, like, oh wow, if if you know, Roger Goodspeed had not sailed from England to Massachusetts in the sixteen thirties, would I ever exist? You know, those sorts of things. And then when I became a father, I've got two teenage girls now, and you know that immediately brought to bear just how urgent and mysterious heredity can be. Because now they're these two people walking around who have inherited a lot of my genes, and you know what, what is it that I'm giving them that that suddenly be the very pressing issue? And I guess what really then kind of crystallize it all for me was that in the past few years, I've been doing a lot of reporting from the New York Times and elsewhere about the real revolution happening in biology, allowing scientists to sequenced DNA, to rewrite DNA, and to also look at other kinds of biology that might help, uh create this thing that we call heredity. H And so it just it all kind of came together and I realized that this would be something that I really wanted to spend a couple of years really exploring deeply. So you mentioned the idea of the sort of personal curiosity about our ancestors, and you talk in the book about how we often do family genealogies to sort of learn something about ourselves, as if the seeds of who we are are somehow present in our really distant ancestors. But how many generations back do you have to go before those relationships with our ancestors really don't matter all that much in terms of genetic closeness. You know, you don't have to go back that far. And that just has to do with how parents passed down their DNA to their kids. You know, we each have two copies of each gene for the most part, but uh, you know, parents only passed down one copy of a given gene to each child, And so if you repeat that process generation after generation, there's a sort of a kind of a stochastic, kind of random process that will basically lead to you know, uh, some descendants not having any DNA at all from a particular ancestor. Um. There's only so much room in your genome and you can't pack in all the DNA from all your ancestors basically, and so geneticis have done some back of the envelope calculations and if you go back let's say ten generations, um, that would be like your ancestors in the sixteen hundreds. Uh, maybe only about half of them have a genetic link to you. The rest they're still your ancestors. But you cannot point to any piece of DNA in your genome and say, oh, I got that from from this particular person you know. So um, So I think that actually, like really shows how we have to, um think think bigger when it comes to heredity. It's not just some particular bit of DNA that that gives heredity its meaning. Well, on the other side of that coin, um, could you talk a little bit about what the Yale mathematician Joseph Chang discovered about human ancestry. It seems sort of like the flip side of what you're just talking about. Yeah, I mean, so, you know, so much about heredity is counterintuitive and almost you know, it seems to contradict itself, and that's in a way what makes it so fascinating. So I just told you about how if you go back a certain number of generations, you're gonna encounter their ancestors from whom you've inherited. No DNA at all. Um. But there's an interesting feature of human ancestry, which is that, um, you know, people uh, everybody today, Uh you know, it shares a common ancestor with some people who lived about five thousand years ago, roughly speaking in other words, UM, if you if you, it's just uh you can and you can figure this out as just Chang did, just by looking at genealogy is a mathematical problem. Um, just think of think of our genealogy is a kind of a branching network. Um. The thing is though that uh you know are if you think about your family tree, um, and you think, well, there's me, and then you branch off to your parents, and then they branch off to their parents and so on and so forth. Um. If you just keep branching in that simple way, you're gonna end, you know, a few thousand years back with more ancestors than there are people who have ever lived. You know, we're talking chillions of people. And that's absurd. So so that's actually not a realistic model of your ancestry. The fact is that your aunt all of you know, your parents are cousins now either that you know, in some cases first cousins get married, but in other cases they're very distant cousins. Another what that means is that your parents share an ancestor, a common ancestor somewhere in the past. It could be hundreds of thousands of years ago, but it doesn't matter. They have an ancestor. So what that does is it folds the family tree back in on itself. And what Joseph Chang realized was that that actually does something very interesting to human ancestry. What it means is that you do not have to go back very far to find somebody who is the common ancestor literally everyone on earth. Uh and uh, it's just in the past few thousand years that you could find people like that. Um. Now, of course you know those common ancestors, you know they for each of us that that's one person or a few people out of thousands upon thousands of ancestors. But it's something that ties us all together. And the irony is that you know, people are really uh uh really love to connect themselves to someone famous, you know, like, oh, did you know that I am descended from Lilliam the Conqueror. And the fact is that probably probably everybody of European descent is and is a descendant of William the Conqueror. Probably everybody of European descent is a descendant of Charlemagne Um. And you know, it's possible that everybody on earth is a descendant of you know, maybe Cleopatra. It's like, that's just the nature of human genealogy is that it's we're all descended from kings. That doesn't make anybody special. Well as as long as we're gazing backwards in time, here, can you tell us how ancient thinkers contemplated heredity? The weird thing is that they really didn't, and they at least they didn't think about heredity in the way that we do. Uh. You know that if you go back and you you look at what Hippocrates would say or Aristotle would say, Uh, this, this whole model of how we inherit something you know, microscopic and biological that that determines how we ended up the way we are just would not compute for them. And so you know, you know, someone like Aristotle would say, like, well, you know, the reason that one generation looks like the previous one is just because it's the same chemistry. Um, you know, of course you're going to be the uh, you're going to be the same because you know, it's the same set of processes that produced a person that produced you. So what's the big deal? And you know, the word heredity, you know, it's a very old word, but it only referred to basically inheriting stuff. Um, you know, and I'm talking not talking about jeans, I'm talking about houses. Uh, you know, farmland, things like that. You know, So in the Roman Empire, there are lots of rules about you know, who got to be an heir, and that's what the word meant at that point. And it's really fascinating, Like you have to you have to wait a long time before you start to even see the first glimmers of how we think about heredity today. Um. My favorite example is in the fifteen fifteen, around fifteen eighty, uh, Montana this this famous essays. He writes an essay about his father because Matennia now is is starting to get older and he's developing kidney stones, and it occurs to him that his father had kidney stones and around the same age and He basically writes Sussi saying, well, what is up with that? Now? Did I get these kids stones from my father? And like, if so, how because you know, when I was born, my father was young and he didn't have kidney stones, So what exactly went from him to me? Um? And you want to just you know, shout at the page like it's it's Janes, it's Jeans. But you know he can't hear you, you know, like he his question went fundamentally unanswered for centuries. Um And so yeah, so so uh, it's really need to look back and and see how. You know, the way we think is not how everyone always thought. You know, the way we think about heredity is is a product of really the modern age. So did the selective breeding of animals and plants inform classical and medieval thinkers at all about the possible nature of heredity, because it seems it's I mean, it's kind of seems like people such as Aristotle or Albertus Magnus would have would have looked at how we bred flowers, crops and farm animals more were, at least in addition to the influence of geography or experience, you would think, so I would I would have thought so. But I think that's because we are in the century and we look back and say, well, everyone must have thought the way we did. But there are actually, you know, whole books written, uh you know by Roman writers about farming for example, UM, and you can search them as I mean, I have sat down and look through these books for anything resembling what you're talking about, and it's just not there. They do not talk about, oh, well, there's some you know quality in this particular variety of olives that you know, if you if you if you bread it, it will pass it down to two future generations of olive trees. That this isn't there. Instead, they'll say like, well, make sure that you know you're you're growing it on good soil, make sure your your farm gets a good supply rain. It's all about the environment. And it isn't really until I would argue, it's not really until the seventeen hundreds that uh, you start to see these farmers, these livestock breeders really take interest in this, UM. And part of it is that these European countries are all um looking for ways to use science to uh make their countries wealthier. And you know, they're thinking, well, if we can, we can, if we can produce new varieties of animals implants, um, then we we will enrich ourselves. Uh. And there's this one breeder named Robert Bakewell who produces an entirely new breed of sheep just by starting to think about heredity, to think about which individuals those sheep is he gonna mate together? Is he gonna just only mate within his flock? Is he gonna go pick out other ones from other flocks to mate? Um? And lo and behold he produces this this very successful new breed. And you know, people like Charles Darwin look at that and say, what just happened? How did they do that? Um? And in Germany and in Central Europe there's a big push to do the same thing with sheep, to do that with crops as well, and uh and to try to understand what are these rules. And one of those people who's trying to understand those rules is none other than Gregor mendel Um. So his his breeding experiments, you know, the foundation of genetics comes out of this new push to try to use heredity to enrich nations. All Right, we're gonna take a quick break and then we're gonna jump right back into the interview and we're back. So at what point does the modern idea of heredity really emerge. Well, I'd say in the late eighteen hundreds, UM, people start to talk about heredity as a scientific question. And Charles Darwin is really important in all of this because, you know, he he comes up with the theory of evolution and it depends on heredity. In other words, Um, you know, the only way for natural selection to work is so if parents can pass down traits to their offspring to give them some advantage and surviving and reproducing. And so it's very obvious to Darwin that, you know that that heredity is this huge glaring question in the middle of his theory, and he and he works really hard to try to find out for himself how heredity works. And he's he's very aware of a lot of the research that's going on at the time, looking to the discovery of cells and the discovery that there are little things inside of cells, but no one's quite sure what they are. UM. And so he develops a theory that there are particles in the cells throughout our body that they somehow stream into the eggs and sperm and uh then become something like we the way we think of genes um. That doesn't pan out. You know, his cousin, Francis Galton, tries to test it by injecting blood from uh, you know, black rabbits into white rabbits, you know, different colored rabbits, and seeing if that changes the color of their offspring. Doesn't happen. Uh and uh So it's not really until after Darwin is dead that scientists start to really understand chromosomes and then rediscover mental and it all clicks together, and the science that they that they call genetics is born in nine uh and and you know, the it's really you can see how exciting it is for the scientists at the time. William Bateson, who coined the term genetics. He he writes at the time that you know, the science of heredity has been red illuctionized. You know that finally they feel like they can they can understand heredity um in its fundamental basis. So so how do we go from this point of of of just excitement and discovery and just fall so steeply into eugenics and then ultimately the horrors of the third Reich well, if you look back, the roots of eugenics UM go back pretty far. UM. You know. So Uh. On the one hand, uh, so our modern conception of race uh starts to develop as early as really the fifteen hundreds are the fourteen hundreds, even where in Spain, UH, Jews are are being considered a separate race of people, and and and noble families have to do have to draw out genealogies to prove that they don't have any Jews in their in their ancestry. Um. Other wise they you know, they won't be able to get that good job in government or so on. And so that starts to develop this idea that that groups of people are fundamentally different in some way that is carried on from one generation to the next. Um. Then uh, in the in the eighteen hundreds, you start to see, you know, a real concern about UM poverty and crime and and a lot of people start to to make claims that these are being carried down in certain families. You know, there are these bad families and why is it that one generation is just as bad as the previous one. And you know, people talk about some sort of hereditary curse that they must have and and then you know, how do we keep that curse from being propagated. And so then when genetics gets discovered, UM, a lot of actual genesis themselves and uh and other and others say well, aha, like here's here's the basis for what we've been talking about for decades now. UM. And you know, the word eugenics had actually been coined in eighteen eighties by Francis Coulton, Uh, Darwin's cousin, and he just thought, well, you know, if intelligence is inherited, then why don't we just essentially breed people away we breed sheep, So you just pick out the individuals who seemed to have you know, the most genius he would call it, and then encourage them to have lots of kids. And and he had these dreams that to produced what he called the galaxy of genius in the future. UM. But by the time that eugenics arrives in the United States and genetics emerges, it takes on a much darker cast because people say, well, what we really need to focus on is these people who have who we believe have genes that we don't like, and we want to prevent them from reproducing, because that's going to drag down our country, and so what are we to keep them from reproducing? And um that leads to sterilization and much worse. So in reading your chapter about Henry Goddard and the origins of the American eugenics movement, I'm struck that this is a potential example of the dangers of bad research, Like you draw a really disturbing picture of how but like sloppy or fraudulent work that became the basis of Henry Goddard's published writings on heredity can be viewed in some ways is contributing directly to real world consequences, like the horrors of for sterilization in the United States or mass murder in Europe. Do you ever think, when you see bad science or pseudoscience being being publicized today that it could ever lead to such nightmares that even its authors might not have imagined? Uh, you know, I don't. I think that we can't rule out those kinds of possibilities. I mean, it might be very, very unlikely, But if you look at history, you can see how bad science combined with existing prejudices lead to really horrific outcomes. And it wasn't that the science was somehow appropriated by the pseudo scientists or something. Uh. Eugenics was embraced by most of the leading um biologists of the time. UH and Uh, there were different forms of eugenics, you know. So some people were very much sort of concerned, were quite racist and you know, concerned about uh, you know, the white quote unquote race being you know, polluted by other races. Um. But then there were progressives who thought that this was going to be part of their grand plan for making society a better, fairer place. Um. And I think it's really important to look at these episodes in history to see how things go bad. Um. And I think it's I think it's arrogant for any of us to say, well, things like this could never happen again, you know, and somehow we're vaccinated from from these sorts of things. But we can draw lessons from the past, and we can see how, um, how humble we need to be in the face of complexity in in our own biology. You know. We you know, I think we're in like in another revolution, the way we were hundred years ago. You know, a hundred years ago, genetics itself was profoundly new, that gene was a new thing. Uh. Now we're at the point where we're looking at genomes, in other words, all the genes in our in our selves, and we can we can see them down to the atomic detail. Um, but there's still a vast amount we do not understand about it, and UM, you know, we we cannot let that be an opportunity to you. Uh you know, card out our old biases and prejudices and say, oh, I see now science backs up what I was saying all along about those other people. UM, we can't. We just we cannot let that happen. Again. I think that's a really good point. And I also think you can even look at it as there's a flip side to it where modern discoveries of genomics really complicated or in some sense is undermine what many people have traditionally understood as the concept of race within humans. Right. Yeah, So the scientific concept of race uh developed in the in the seventeen hundreds, and it was really um, very much spurred on by, uh by what Europe was doing at the time. So Europe was in the midst of building up huge colonies um and enslaving many many people. There was a need for serve legal and moral justifications for doing this, and a lot of it, uh was based on these concepts of race, so that for example, you know, Africans were were claimed to be a completely separate race uh that you know, had inherent uh inferiority to the white race. And so therefore slavery is okay. And you can see this again and again in in lots of lots of writing at the time. Uh. Now, even in the early nineteen hundreds, Um, there were there were indications that this kind that genetics was not aligning with these these uh old ideas about race, and they just weren't fitting neatly. Um. You it was very it was it was becoming harder and harder to draw any particularly bright line between groups of people. I mean, obviously people are different, uh. You know, there are lots of differences and people in terms of skin color and height and shapes of faces and culture and all the rest of it. But the genes were not supporting these old ideas about race. And by the midnighteteen hundreds of people, a lot of anthropologists and geneticisis were saying, you know, the word race is so burdened with so much that's terrible and immoral and has so little connection with the way we're starting to understand populations. Let's just get abandoned it. Um, that really hasn't that really didn't happen. But nevertheless, like now where we can look at the whole genomes. Um. Yeah, the whole thing with race now is is it just is it's a bit one. The way one genete has put it to me is like, well, you know, like talking for us, like talking about race is like the way Greeks talked about the you know, the four elements air, fire, water, earth, like you know it. You know, Aristotle could explain all sorts of things uh that way, and they seemed good to him. But you know, we know that there's things are much more complex than the four elements, and if you forced physicists to go back to the four elements, they'd be very unhappy. So Jenets they're saying like, please don't make us go back to you know, the genetic equivalent of the four elements. You know, we're you know, they're very interested in ancestry and how populations mixed together, how they become isolated, and all the rest of it. But these old ideas about race and on all the connotations of race they don't map onto it at all, so they just don't want to use it now. Of course, in addition to just the passing on of genetic information, UH, we also have epigenetics. And even as you explore the effects of the microbiome, can can you talk about how these have changed our definition of heredity? So in the eight hundreds, heredity becomes a scientific question. You know, what is it that makes one generation connected to the past? Why is it that generations resemble their forerunners? Um? What what are these connections? And Uh, genetics provided a huge part of that answer, which is that well, genes get copied and then transmitted through eggs and sperm and uh. And so that was a huge revolution and understanding. But that doesn't mean that that is all that heredity can be. I mean there's still the at least the logical possibility that there are other ways that each generation be can be connected to the to the previous ones. And so in my book I talk about different forms of heredity that scientists are exploring. UM and so you know, one one very exciting possibility is what you referred to as epigenetics. And epigenetics is kind of a broad term, but roughly speaking, what it refers to is the molecules inside our cells that control our genes. That that allows some genes to be switched on and to produce proteins and others that are kept silent um. And you know, it's it's very clear that this is incredibly important to our existence. You know, it's what makes your skin cells be skin cells, and you're you know, brain cells be brain cells, like they are using different genes in the same genome. And when these cells divide um the you know, a skin cell does not normally instantly become a neuron or or you know it doesn't you don't grow a tooth on your back of your hand um. And that has to do with epigenetics um. And so what does this have to do with heredity. Well, you know, when those cells divide, they are basically inheriting the genes and the epigenetics of their mother cell. But you know that the possibility arises, well, what if you pass those down to the next general ation altogether, you know, through eggs and sperm um. And there's some evidence that that that can happen. And what makes it especially exciting is that you know, through our lives, experiences can change the epigenetic makeup of ourselves. You know, so if you if you get sick, if you smoke, if you experience stress, those all seem to have an influence. And so the open question is, well, how much can those experiences we have in our lives then influence future generations? UM. I think that the jury is still very much out when it comes to people. UM, But in other species, especially plants, there's lots of evidence that that really is something that happens. You know, a plant goes through a drought and generations later there's still an epigenetic mark on its descendants. So yeah, epigenetics is in a really exciting area. So you just alluded to some of the controversy about epigenetics, and I guess there are other forms of ideas of non genetic inheritance, but epigenetics in some ways still remains controversial, especially in humans. Like you're talking about, if you're comfortable speculating and if you had to guess, how would you imagine our picture of non genetic inheritance might change over the next fifty years or so, what's your sense? You know, I think that it is actually possible that we'll just find that UM. Human epigenetics is just not really that important. I mean, I'm actually I think there's reason to be kind of pessimistic. Um that you know, there are these very cantalizing studies, but they're small and they could just be the result of noise and so on, and and yet you know, we really want epigenetics to be real. Um. I mean, epigenetics has totally taken hold of the popular consciousness. And you know, I was astonished to learn not long ago that you can take classes and epigenetic yoga, which not kidding, you can google it. And the thinking is, the claim is that you know that by doing this yoga you change the epigenetic profile of yourselves and I and you know there are psych psychiatrists who will offer you epigenetic analysis to basically undo the trauma that you inherited from past generations. Um. It really speaks to us in a very profound way. But I actually don't think that science is going to really hold up very well. Um, because are but I don't think it looks like our biology just doesn't really allow that to make much of a difference. But you know, the flip side is that culture, um is actually I I would argue an incredibly important form of fredity, especially for our species. We we pass down not just our genes to the next generation, but all of our knowledge and and beliefs and customs and so on, and those those get pell down through the generations UM in a very hereditary way and UM, and that's actually very different from other species. And I would and you know, in the book, I talked about how you could argue that civilization itself is the product of our very special form of cultural inheritance. So in talking about non genetic inheritance, you've got potentially epigenetics, though the juries out on that, You've got, you've got culture. But we should talk a little bit about microbiology. Can you tell the story of how you found out that your belly button contained bacteria only known to exist in the Mariana Trench? Absolutely? Yeah. So I've been incredibly fascinated by the microbiome, you know, all the bacteria that live on us and in us for quite some time and and I have been doing some reporting on it as scientists have found new ways to to explore our microbiome. And it used to be that you just have to scrape, you know some you know a little bit of skin, or take a stool sample and taken into a lab and try to grow bacteria. And the fact is that very few of the bacteria that live on us uh or in US enjoy being in a petri dish on their own. It just it makes them miserable and they don't grow. So we had a very impoverished view of this inner world until scientists were able to just say, Okay, we're going to grow into this sample and just grab out all the DNA and we're gonna sequence all the DNA and from that we're going to figure out what is in there. And that totally revolution. I studied the microbiome because now you didn't have to grow these critters. You could just fish out their DNA and look at that. So it turns out we have hundreds, maybe thousands of species in our guts and on our skin and so on and um and so you know, one day at a meeting, UM I was walking past a scientist who was holding out a qute tip and he said, I'm doing a study on people's belly buttons. Would you mind giving me some of your belly button lint? Belly button lint, and I want to see what's in there, you know, and for someone like me, you don't have to ask me twice. I'm like, give me that cute tip. So you know, I go off into the bathroom and I you know, fiddle around and don't get in a little tube that they gave me and handed it back, and then they went off and they looked at all the DNA there was on that cute tip, and you know, a lot of it was my own skin cells, but then a whole lot of it was not um. And actually they identified fifty three species as I recall of bacteria just in my belly button, and uh, it was amazing to to look at, uh, the information about each of those species. And so one of them it's had only there's only no own from a sample at the bottom of the ocean. They marry on a trench um. And there's another one that I have that's only been found in soil in Japan. I've never been to Japan, so um. But you know, this was entirely unsurprising to this scientist, because you know, he was looking at lots of people and was finding people with you know, over a hundred species just in their belly button alone, and from all sorts of different places. Um. So what does this have to do with heredity? Well, you know, I I did not inherit that marry on a trench bacteria from my parents. UM. It's just you know, we have all of this, these these bacteria in the environment um, and some of them have become very well adapted to living on our bodies. Um, and we just picked them up um through our life. But it does seem like that the microbiome UM, that there is some heredity to it. UM. The best examples come from certain animals like that passed down bacteria to their offspring. Then these bacteria can only live inside these animals, and without those bacteria, these animals die. The cockroaches are actually a great example of this. So you know, one reason that cockroaches are so successful is because they harbor one species of bacteria in a special little organ um where it breaks down some of their food and gives them nutrients. Um. And these bacteria never live outside of the cockroaches, and actually they're they're sitting inside of cockroach cells. And then in the female cockroaches, those cells crawl over to an egg and rip open, and then the bacteria infect the eggs so that cockroaches are born completely infected with these bacteria. That's that to me just seems that's heredity. I mean, these bacteria are being passed down from millions of years from parents to offspring. Um so the US and now as well. Are is that true for humans? Um? Maybe not, uh, you know, in that particular way, but um, you know, it is possible that there are a lot of species that are very much adapted to us. You know, maybe mothers are passing down certain kinds of bacteria in the birth canal or during breastfeeding. Um. And maybe the most dramatic example of all is that in all of ourselves we generate fuel with these little blobs called mitochondria, which have their own DNA in them. And the reason they have their own DNA is because they started out as bacteria and about two billion years ago and our single celled ancestors, those bacteria infected our ancestors and then took up permanent residence in there and we cannot live without them today. So um so, so MicroB is gonna have a very powerful part in heredity. Do you think our expanding consciousness about the full scope of heredity from like generation into symbiance or even to camerism should force us to re examine our ideas about what it means to be an individual, an individual animal, and what the biological and categorical boundaries of the self really are. Absolutely, uh, you know, I think that uh, you know, heredity does not actually follow a lot of the simple rules that we assume. It does, uh, and it and it does bring into question what it means to be an individual because you know, we think of he started out with some original genome in a fertilized egg, so we inherited half of that genome for me to our parents. It came together in this new combination and that's us. But you know that is not actually us um, and in lots of different ways. So in one way, I mean, if you actually follow the cells that divide in an embryo, those cells can mutate and then utate again and mutate again, so that if you were to look at, say, any two neurons in your brain, they would be different from each other because they have acquired different mutations as we developed. UM. So there is no one genome in our body because we are what scientists say call us our mosaics. UM. But then that's not the not the end of it. UM. So you know, we think of heredity is going down through the generations, but heredity can also come back up in reverse. Uh. And so one example of this is um when women become pregnant, UH, cells from their fetus will circulate around in their blood. You can actually you can actually draw blood from a pre new woman and sequence the genome of the fetus. Uh we that is done on a regular basis. Now uh after pregnancy, uh, those fetal cells may go away because of the mother's immune system is clearing them out. But surprisingly often uh those cells can establish themselves in a mother's liver, syroid, gland, even her brain. And scientists refer to uh such people as chimeras. Um it's after the you know, the beast of Greek mythology. And you can get chimeras also from twins in the womb who are sharing DNA sharing cells uh. And so you can literally like have um. You know that one of the first discoveries of this was a woman who gave blood in the nineteen fifties and totally baffled uh the blood bank because she was giving two types of blood at the same time. And he said, this is not possible, you know, there must be some contamination somewhere. But it turned out that her blood was made up from two individuals, herself and a twin who had died when he was in infancy. Uh. And so you know, and this is not something that's rare. Timerism is probably quite common among humans, and it really challenges these these ideas that we we tell ourselves about heredity and individuality. One of the weirdest and most interesting types of heredity you discussed in the book is that, I think you said of it's eight or so lines of contagious cancer found in nature so far. Can you talk a little bit about contagious cancer and does it make sense to think of this cancer as an independent animal or organism of its own type, or as sort of an infection from an original animals genome. Yeah, this is where heredity gets really weird because us, you know, when when cancer arises in our bodies, it's a it's another one of these cases of mosaicism. In other words, Uh, these cancer cells are gaining mutations that the rest of the body doesn't have, and those mutations allows them to reproduce quickly and to be very aggressive and destructive. Now, Um, cancer usually uh, you know, either is wiped out by the body or is lethal. In either case, you don't have cancer surviving beyond the life of its host. We we think of that as being weird, but it turns out that in fact cancer can endure um And this was really first discovered um in in a uh in a case with dogs where dogs would be uh developing um these these tumors uh. And it was very odd that they the cancer seemed to spread like an infectious disease, and so people scratching their head over this, and then they realized that actually what had happened was that the cancer cells themselves were spreading from one dog to another to another UM and so that the cancer cells were not in fact related to the dogs that they were in. And if you look at the DNA of this cancer, it goes back to some dog that lived maybe ten thousand years ago, and it has just been spreading from dog to dog ever since, and it's been mutating along the way. And it's and so it's the thing that you know, it's it's what do you call it? I mean, I don't know what we could call it, but you know, some have argued that it should be just given its own species name because it's it's this, it's this lineage of animal cells that has its own genome UM, and has its own way of getting around in the world. It's it's doing just fine. UM. So surely it deserves the name UM. And then it turns out that in a few other cases scientists have found another species, so Tasmanian devils in Tasmania, they get a facial tumor because they bite each other when they're fighting, and they spread this cancer to each other. UM. And this this cancer has actually arisen a couple of times in Tasmania just in recent decades, so it isn't something that only happened once a long time ago. And what's most mind blowing is that some scientists stumbles across this yet again, just in the past few years uh in clams, in shellfish UH, and have discovered that there there's contagious cancer in the ocean. UM. So you're swimming. As you're swimming in the ocean, you're swimming around cancer cells that are moving from host to host. An infectious cancer as its own type of organism. What kingdom of life would that be? Would it be an animal? I? Yes, it would be an animal simply because it's descended from animals. Yeah, I mean I would say they would have to be given, you know, a place in the animal kingdom. But and you know, maybe you should just still call it like a species of you know, maybe the dog cancer should be a species of dog. Maybe you know, cana is cancer or something. I don't know. I don't know, um, but you know it's and you know, when when and when you talk about or what makes up an animal, you know, like, uh, what makes up up us? You know, like we think of cancer cells as being part of ourselves. They they originate from our own selves. But um, imagine if your body was actually made up of your own cells and then cells that came from someone ten thousand years ago, that that would be weird. Yeah, alright, time for a quick break. Then we will be right back for more of our versation with Carl zimmer Than. All right, we're back now. We can't talk about the future of heredity without touching on Crisper. How is this technology affecting the future of human redity? Well, you know, we're going to have to wait and see exactly what happens, but certainly the potential is profound um. Crisper is just a few years old, and it's this is this technology essentially to zero in on any particular bit of DNA, cut it out, and if you want, insert a different little stretch of DNA in there. So um, this raises the possibility of being able to cure hereditary diseases by rewriting uh, the DNA in cells, you know, to repair a faulty gene. But what some scientists have been already exploring is, well, what if you take human embryonic cells. What if you take you know, human embryos are just a tiny little cluster just you know, seven or eight cells, and you use Crisper to rewrite their DNA. UM, let's say you fix a hereditary disease in just this handful of just as few cells. Well that if if you if that if a person were to develop from those cells, they they would have Crisper altered genes throughout their whole body, and if they were to have children, they would pass on those Crisper altered genes as well. And so you know that that that these experiments have already begun on on these tiny little human embryos, and so really, you know what what needs to happen now is for us to have a really a kind of global conversation about whether we want to use this or not, whether it's safe, whether it's ethical. UM, how do we feel about who should have access to this? UM? Do we have the right to alter future generations? Um? And you know we and maybe we'll feel comfortable with, say, you know, eradicating Huntings disease. But what if somebody says, well, yeah, but I want I'm using IVF and I want to just give my kids, Uh, this mutation that we know reduces your odds of getting Alzheimer's? Could I do that as well? And then you know what if you add on other things? What if you add on things that are not don't have to do with immediately treating some ready to disorder, but you know, change a trait, change, hair color, change, height, change, all these things are are people are going to be comfortable with that? UM? And this all you know this science fiction writers have had a monopoly on this conversation until now, but I think that everybody else needs to be talking about it too. Now. As far as crisper altered genes go, given like a near future scenario, would they be detectable. What would somebody be able to say to to look at individual's genome and say, oh, well you've had there's gene altering evidence here. Or would a future civilization be able to look back at our genetic information and say, oh, well look here in this particular family line, we see evidence of of of of crisper alteration. That's an interesting question. Um, I think you would. I think that it would be possible if the people doing the crisper changing um left behind, you know, a mark of what they were doing, you know, a little water mark. Think of it that way. You know, some distinctive sequence of non coding DNA nearby that basically says hello, you know, this is this, this crisper alteration has brought to you courtesy of such and such hospital. You know, Um, you could totally code a message in DNA people. You know, people have enquoted entire books in DNA. Now, so you could do that. Um, But if you if somebody decided not to leave a water mark, then no, Actually, I think it might be very difficult to UM to say, oh, well, this person descends from a crispered ancestor knowing knowing tech companies I know we'd end up with like thirty page ELA agreements in there. Sure, absolutely, But you know the problem is that you know that over the generations they would get that agreement would mutate, and uh, you know, the legal language would would change into things that the lawyers didn't have in mind. So, given the great power that Crisper has to to allow us to alter our genes, what what do you think are the best ideas you've heard about how to guide it in a way that's that's fair, that's going to have good outcomes and not bad it. Uh, you know, the people have access to in in equitable ways. I mean, have you encountered anybody who has done the best what you would consider the best thinking so far on the ethics of gene alteration? You know, I I in the United States, the government is really just being very uh emphatic and not wanting to really talk about these issues at all. So uh, you know, not only is it not allowed to do germ line modification, but you can't do any research that might lead to that, and so um, we're not really having a meaningful conversation in the United States yet, I think, um, and uh, Unfortunately, what that means is that people are going to want to go to other countries where there is no particular regulation one or the other and do that in you know, in um, in you know clinic sort of on that are hidden from view. UM. And in my book I talk about one case where actually this has already happened. UM. A couple went to Mexico and an American doctor joined them there to uh to basically replace the mitochondria in this woman's eggs with with healthy, healthy ones. UM. So you know there are some genetically modified people alive today. UM. There there are a few, UM, but they're they're already here. UM. But they I think that it's a better, better way to deal with this is what England is doing. So in England this treatment called mitochondrial replacement therapy. UM. There was there was a lot of research that was done on it, UM and using animals, using using you know eggs, human eggs and so on and then UM and then Parliament actually had a big full debate about it and you know, the advantages and the possible risks and the ethics and so on, and then they decided, well we're going to allow this to happen, but it's going to happen under these rules. So you know, you can't just like walk into any doctor's office and get this therapy like that. You know, we're gonna really make really uh take We're gonna take real care to make sure that this has done safely and responsibly and under the right circumstances. And so now there is a university that has actually you know, gotten permission to basically open their doors for business. UM. And I think that's the way to go UM, because then you can you can have these discussions and say, like, you know what, as a society, we don't want uh people to be trying to make their kids more intelligent by altering their genes. We think that's a that's bad for individuals and bad for society. We're not going to allow it. UM, And that will actually happen rather than sending people to other countries to have you know, possibly dangerous treatments. UM. That's the way I think UH things should go. UM. And you can see an example of it in England, And it would be great if if the United States could follow suit. You know, on this show a lot we talked about how often like science fiction is sort of the playground for people working out these problems before they're dealt with in the real world. Have you encountered any any science fiction or fiction in general that you thought did a good job of dealing with you know, raised the interesting questions, had intelligent things to say about the implications of genetic engineering and humans. Oh yeah, I think that there's a long tradition of genetic engineering in science fiction. Um and uh and even before people really knew what genetic engineering was. You know, Brave New World is a fascinating book even now. I mean, and it's amazing think when you think how um, how much uh uh was just only discovered after the publication of the book. Um and I it's I find that one quite quite prophetic. I think the problem with science fiction comes when people think that anything can happen. That when people think that biology allows anything you can imagine to be a possibility. Um and the fact is that biology doesn't work that way. And so you know, when when we're actually talking, you know, today about well, what are the real possibilities that Crisper could create, I think we need to sort of I think we need to make sure that we're not um, just letting our fantasies run wild. You know, some people have said like, oh, well, you'll just be able to um Cristoper your kid and turn them into a genius. Um, and that it's not what science indicates. I mean, you know, intelligence is this incredibly complex phenomenon that is, you know, influenced by genes, it's influenced by the environment. It's partly a social thing, you know, in terms of like you know, intelligence really sort of gaining its meaning in you know, in a society. UM. And you can't just zoom in on a on a few genes and make a tweak here and there and say ah ha, like now my child is going to you know, get into the very best colleges. It just does not work that way. Um. And and I think that if people just go ahead with it anyway, UM, those children are going to be born, um, not just with these odd little changes to their genes, but with a whole huge set of expectations um from their parents. You know, I spent a hundred thousand dollar. There's a change your genes to make you a genius? And why are you getting these grades and math? What's what's wrong with you? I just see a That's where I see the real dystopia emerging is just expecting heredity to do much more than it can possibly do, uh to to alter ourselves. That's really interesting and it raises another question that definitely comes up in the book, which is that even when we're talking about traits that are to some large extent heritable, what are some of the reasons that it can create misunderstandings for us to talk about there being quote a gene for a certain trait. Yeah, we really have come to look at genes as being all powerful and and that is a real mistake and it's but it's hard to really, um get your head around the paradox of heredity in this regard um. And one of the examples I like to talk about is height. You know how it seems like it's simple, like it's just just a number that you get off a tape measure, Like how hard could that be to understand? But you know, in in fact, um, you know, heredity is this very weird mix of genes in the environment. Um, you know gene so height is is very what scientists say are very heritable, meaning that if you look at the variation among people in a particular population, why are they tall? Why they're short. Uh. You can explain a lot of that because of the genes that they inherited from their parents. So tall parents tend to have tall children. Short parents tend to have short children. And it's so that means it's very heritable. UM. But that does not mean that, you know, height is somehow um locked in and fixed that. It does not mean that you can actually, you know, finally predict um the you know, how tall it could will be just based on their gene. In fact, we didn't even know about any of these genes until the past decade or so. Uh. And now scientists are discovering literally thousands of genes that influence height, each one in a tiny little bit. You know, I got my genome sequence and discovered you know that I had very interested to find that at one particular gene was the first gene that was ever linked to height in population. And I'm I'm about an eighth of an inch taller than it would be otherwise because of the variant that I have. So you know, it's it's almost invisible. UM. But you know, the genetic influence just is the sum of all of these different variants. Um. And yet on top of all of that. UM. You know, you can have, you know, all the tall genes you want, but if you're not getting a good diet when you're a kid, and if you're facing dysentery on a regular basis, you're just not going to grow that tall because your body is going to be basically channeling all those resources to fighting disease and to you know, fight defend against starvation. And you know, on top of that, even more amazing to me is that in the whole world has actually gotten several inches taller over the past century because life overall is better. You know, there's more people have a better nutrition, better medicine. UM education probably plays a role in this. Uh. And so it's not that people inherited you know, quote unquote tall genes, it's that they inherited a world that favors greater height. So I've got one last question that might be kind of weird, but we'll see what you think of it. I often hear hear people talking about UM their relationship with their own genome, UM with their own genes in two basic ways. One is self identification. You know, it's like my genes are why I am like X. And so there there's a sort of I identify with my genes and lady. And then there's a kind of antagonistic kind of thing people think about with their genes, like the genes are this other disembodied force that made them and it's almost like another person that they have to negotiate with in some way. To what extent do you, given all of the research you've done and after having written this book, to what extent do you feel you are your genes or that your genes are this separate other force from you as a person. That's interesting. I yeah, I've heard that kind of language too, you know. And people will get their DNA sequenced and they'll discover they have a particular variant linked to some trade and say, ah, well that's why I do X Y Z or or they'll discover they have ancestry from a particular place and say, ah, well, that's why that's why I like to tell stories, or that's why I like to run, or what have you. Um And you know, you see ads on TV for these companies like ancestry dot Com that play on that exact attitude towards our genes that somehow, you know, what we do in our lives is encapsulated in these genes that we inherit from our ancestors. Um. And then yeah, then there are people who just want to fight against it, um, you know, and part of that sometimes feels like, you know, it's it's sort of a displaced fight they're having with their parents, you know, Like I'm not gonna be like you were, you know, and I don't care if I inherited genes from you. I'm going to be my own person, um, I would say, in my own experience. UM. You know, I got my genome sequence and part of the research for this book, and I really looked at it very deeply. It's been a fascinating experience. But I can't find anything in there that is quote unquote me. I think that it's just not there, you know. I I was able to look at the genes that I inherited from neandertals, you know, tens of thousands of years ago, and you know, which is fascinating. But then I say to these scientists, Okay, you've given me this catalog, got the indertal genes, let's talk about them, Like, what what does it mean that I inherit this particult? Like, here's one gene tell me about it and the sciences to be like, well, it looks like no one actually knows what this gene does at all, you know, and then that you're just sort of left there. But with the state of the science, you know, maybe I found that I have in the andertal gene that UM is linked to an increased risk of nose bleeds. I don't know. I don't know what to do with that, you know, And I it also makes me wonder why the inertals might have nosebleeds. But that's a whole separate issue. But you know, I I I don't I. I can't say that anything I've done looking at my own d d n A has given me some deep insight about my inner self as a person, you know, as it's much more relevant to me to think about, you know, how my parents raised me and what my experiences were as a kid, and what it has been lie you know, being married and and and being a father, like, the lived experience matters much more to me than UM than the details of the genome I inherited from my parents. UM. And that's that's kind of where where it stands for me now, all right, Yeah, well, well thank you so much, Carl. It's been a real pleasure talking to you today and we appreciate you taking time to speak with us. My pleasure, my pleasure. I really enjoyed the conversation and I'm glad you enjoyed the book. So there you have it. Thanks once again to Carl Zimmer for coming on the show and having this wonderful chat with us about his new book, She Has Her Mother's Laugh, The Powers, Perversions and Potential of Heredity Again. That's available in hardback, as a digital and as an audio book right now, and you can check out Carl's website Carl Zimmer dot com for even more about him and his projects. That's right, go to that website, and hey, be sure to check out our website as well. It's Stuff to Blow your Mind dot com. That's who you'll find all of our episodes. You'll also find links out to our various social media account so you can check those out as well. I want to remind everybody if you want to support the show, one of the best things you can do is rate and review us wherever you get your podcasts. Big thanks as always to our wonderful audio producers Alex Williams and Torry Harrison. 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