Something You Should Know - How Your Family Affects Who You Are & How DNA Affects Your Health

Episode Date: June 12, 2025

A lot of things impact an employer’s decision to hire you or not. But one thing you may not have considered is where you fall in the order of interviewees. Listen as I explain why you want to be the fourth person interviewed. ⁠https://finance.yahoo.com/news/why-always-fourth-during-round-191931348.html⁠ Why did you turn out the way you did? Was it because of your parents, your siblings, your environment or all the above? What about birth order - does that really influence the direction your life takes? What do parents of successful kids tend to do more than other parents? All these questions and more are answered in my discussion with Susan Dominus. She has looked at the research on this and found that a lot of what we believe about how kids turn out is wrong. Susan is a writer for the New York Times and author of a book called ⁠The Family Dynamic: A Journey into the Mystery of Sibling Success (https://amzn.to/3ZgfK6z).⁠ Did you know that compared to many other species, humans have a high rate of genetic diseases. Wouldn’t you think by now that evolution and "survival of the fittest" would’ve weeded those out? What science has recently discovered, about DNA and genetics is astonishing and is helping us understand how genetics work, how diseases are passed on, how genes can mutate and make us sick, why we have such a high rate of genetic diseases and how we may soon be able to fix or prevent some of it. Joining me to discuss this is Lawrence Hurst. He is a professor of evolutionary genetics at the Milner Centre for Evolution at the University of Bath and author of the book, ⁠T⁠he Evolution of Imperfection: The Science of Why We Aren’t and Can’t Be Perfect (https://amzn.to/3ZgOjJS)⁠⁠ There are things in your kitchen you need to get rid of. Over time we bring things into the kitchen that we never need, never use that take up a lot of valuable space. Listen as I offer some suggestions on what you can get rid of right now with no regret whatsoever. ⁠⁠https://www.delish.com/food/a63527523/6-things-you-should-never-keep-on-your-kitchen-counter-according-to-organizational-experts/⁠ PLEASE SUPPORT OUR SPONSORS!!! MINT MOBILE: Get your summer savings and shop premium wireless plans at ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://MintMobile.com/something⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ ! FACTOR: Factor meals arrive fresh and ready to eat, perfect for your summer lifestyle! Get 50% off at ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://FactorMeals.com/something50off⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ ROCKET MONEY: Cancel your unwanted subscriptions and reach your financial goals faster! Go to ⁠⁠⁠⁠⁠⁠⁠https://RocketMoney.com/SOMETHING⁠⁠⁠⁠⁠⁠⁠ QUINCE: Stick to the staples that last, with elevated essentials from Quince! Go to ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://Quince.com/sysk⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ for free shipping on your order and 365 day returns! INDEED: Get a $75 sponsored job credit to get your jobs more visibility at ⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠https://Indeed.com/SOMETHING⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠⁠ right now! DELL: Introducing the new Dell AI PC . It’s not just an AI computer, it’s a computer built for AI to help do your busywork for you! Get a new Dell AI PC at⁠⁠⁠ https://Dell.com/ai-pc⁠⁠⁠ Learn more about your ad choices. Visit megaphone.fm/adchoices

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and cemetery providers owned and operated by affiliates of Service Corporation International. Today on Something You Should Know, when you get interviewed for a job can have a big impact on if you get the job. Then, how did you turn out the way you did? Was it because of your parents, your environment, your siblings? The way I often talk about it is parenting effects are probably overestimated by the general population and sibling effects are probably underestimated because there's just shockingly little research about how siblings affect each other.

Also, why trying to appear younger than you are usually fails, and how your DNA works and the amazing advances in that field. So when the human genome was first sequenced, all that DNA, it cost $3 billion, it took about 15 years. We can now do exactly the same for around $100 and it takes an afternoon. This is a revolution in medicine. All this today on Something You Should Know. What does it take to lead like a superhero?

Well, find out on the Superhero Leadership Podcast, hosted by Marvel's former CEO and legendary turnaround expert, Peter Cunio. Each week, Peter is joined by top performers from business, media, and beyond, leaders who have mastered the art of impact, resilience, and vision. Together, they explore Peter's 32 leadership essentials, revealing what it really takes to rise, inspire, and lead with purpose. If you want to level up your leadership, this is your blueprint.

Search for Superhero Leadership, available wherever you get your podcasts. Something you should know. Fascinating intel. The world's top experts and practical advice you can use in your life. Today, Something You Should Know with Mike Carruthers. If you're looking for a job, or the next time you are looking for a job, I have some information that you might find very useful. Hi and welcome to this episode of Something You Should Know. When a company is interviewing people for a job on any given day, the fourth person

interviewed that day is more likely to get the job. Researchers from Old Dominion University in Virginia analyzed more than 630-minute job interviews at a university career center. They found that the fourth person being interviewed got the most attention from hiring managers. While it's become popular belief that employers often make snap judgments about a potential candidate within the first few seconds of the interview,

this study found that decision-makers take closer to five minutes for the first interviewee and reaches closer to eight minutes by the fourth applicant. After this, however, the time hiring managers take to reach a decision begins to decrease with each additional interview. And that is something you should know. Have you ever sat back and thought to yourself, how did I turn out the way I did? Or how did my kids turn out the way they did? Often people lean on the idea that you turn out the way you do because of how you were

parented or because of the family you grew up in. And then you hear things about birth order, that you are more likely to be a certain way if you're the oldest, or if you're the youngest, or if you're somewhere in the middle. What about all of this? And what about that idea, and we've all noticed this, that multiple kids grow up in the same house with the same parents, yet they all turn out so differently. Well Susan Dominus has looked at the research on this and uncovered a lot of really interesting findings.

Susan is a writer who has been with the New York Times for several years and she is author of a book called The Family Dynamic, A Journey into the Mystery of Sibling Success. Hey, Susan, hi, welcome to Something You Should Know. Thank you so much, Mike. It's a pleasure to be here. So what about all these theories about how people turn out the way they do, how kids turn out the way they do? You'll often hear people say, well,

oh, that's because he's the oldest, or oh, he's a middle child, so that's why that happened. There are a lot of misconceptions about why kids turn out the way that they do. So that's why that happened. There are a lot of misconceptions about why kids turn out the way that they do. And some of those misconceptions are about parenting effects. Some of those are about birth order effects. Families are really messy and complicated things.

And it's almost a mythology or an astrology that we impose on our own families to explain why things happen the way that they do when there are many other factors involved that people I think underestimate. Well so we hear things like for example you know first borns are likely to do this and younger siblings are likely to do that and is that science or is that just not? Yeah so it's true. You often hear people saying things like as if it was just a given fact. They'll say, oh well she's you know the spoiled one because she's the youngest or she is the most conscientious because she's an

oldest sibling. What turns out to be true is probably not that. The best research that has been done on birth order, the biggest studies, the best constructed studies, basically find surprisingly little correlation or no correlation between birth order and personality. So for example, we tend to think of the oldest child as being the most conscientious in the family. What we underestimate is the role of developmental psychology and why it feels that way. So let's say there's a 17 year old in the family, that 17 year old may well be the most conscientious person in the family. But the 14 year old little sister, when she gets to be 17 years old, might even be more conscientious than the 17 year old.

Even you're older, you're gonna be more responsible. It's just a kind of developmental quality. So the other thing is that the person who's the most conscientious in their own family might not even be that conscientious relative to the general population. So does birth order determine anything? Or is that just one of those pop psychology things

that seems like birth order should matter and it doesn't? Or does it tell us anything? There's one finding about birth order that is remarkably consistent. The oldest child in a family tends to have a cognitive edge. It's this is on average, you know, I am the youngest of three, so I need to point out that this is on average, and these effects are not huge, but it's really consistent. And the reasons for that are pretty interesting and maybe even a little bit intuitive. And when you say they have a cognitive advantage, you mean what? They're smarter or that they do better in school or academically?

Has a little bit of an academic advantage. Okay, so go ahead with tell me about the cognitive edge that an oldest child has. The first child is the only child in a family of siblings, whoever gets to be the sole focus of their parents attention. And they get that sole focus at a time that's really developmentally crucial. So they're getting all of the enrichment, all of the attention, all of the eye contact at a time when their synapses are firing like crazy

and forming like crazy. And so parents might love all their children equally, but the second child is always gonna have less of their parents' attention than the older child did during that time when that child was an only child. So that's one reason why researchers think that oldest children have this cognitive edge. And by the way, they see this cognitive edge even when that child is only a year old. They do better on tests that

you know they give to babies than their younger siblings do when they reach the age of one. So it's really remarkable and it starts really early. However, it increases over time this this gap. And the thinking is that when kids get older, older siblings do a lot of instructing of younger siblings and that there's something that is consolidating of knowledge or is instructive or salient and healthy somehow for cognition in just doing a little bit of that teaching. So when we talk about, as we started talking about,

how a kid turns out, how a person becomes who they are, what can you attribute to that? What does affect how a kid turns out? When researchers look at twins, let's say they look at fraternal twins, and they try to figure out, okay, well, how much does having a shared environment, being raised in the same home, make them more similar than two people

who were raised in different homes? The answer generally is not that much. And as the mother of fraternal twins, I can speak to that. My fraternal twins came out incredibly different. They remained incredibly different. What does matter about being raised in the same home is whether or not you're gonna go to college. That's something that kids raised in the same family

tend to have in common. And that's hugely consequential for your income and your income affects so much of who you're likely to be and how you're likely to fare. But in terms of whether you're going to be equally conscientious, whether your kids are going to be equally creative, you know, parents can expose their kids to those things. But whatever they do in the household seems to have much less of effect of an effect than then parents really imagine.

Well, what about things like morality? I mean, that is something that seems to get passed from parent to child. The values you grow up with seem to stick. Yeah, I think that values certainly can be passed down from parents. I think that's what's a little harder to measure are things like personality traits.

Like, how much does parenting make somebody outgoing or introverted? These are the kinds of things that we associate, for example, with success, like conscientiousness. Can parents, quote unquote, make their kids more conscientious? It's unclear. And many researchers would say, probably not. You know, that's not to say that kids come into the world

and how conscientious they're going to be is 100% determined by like their genetics. No, how you're going to be, you know, how you're going to turn out is a combination of the sort of genetic nudges that you get from the get go and the environmental effects that are part of your life. Now when we talk about nature and nurture, we think about nature, genetics, and nurture, parenting. But really it's genes and environment that we're talking about. And parenting is just a small part

of the whole picture of the environment. The environment is the school you go to. It's the neighborhood that you grow up in. It's the you know, who is your best friend? It's what nature documentary did you watch when you were in fourth grade? It's did you break your leg when you were in second grade? Was your bedroom sunnier than your brother's? The environment is vast.

It involves huge amounts of chance. And it's sort of like you come into the world a certain way, you interact with the environment and all of the random haphazard things that happen to you. That changes you a little bit. Now there's a new version of you interacting with every other random element that you come across. Parenting is part of that for sure. It's just a smaller part of it than most people appreciate. What about major traumatic events that happen to a child? Do those have a disproportionately large influence on a child's development?

So there's something known as an adverse childhood event. Those are things like abuse or exposure to violence at a very young age or trauma. And we do know that that actually does really change the brain. So if you want to talk about parenting effects, it's probably most profound at the extremes. So like, you know, sort of what people call good enough parenting, you know, parenting that's basically healthy, insane, that's not going to have a huge impact one way or the other on whether your kid is super conscientious or not.

If parents are abusive, they can really do serious damage to their children and then they can really affect their children's lives. At the other end, I'm not saying that the opposite of abusive is overly involved with your kids extracurriculars, but if you look at somebody like Richard Williams, right? Like Richard Williams, the father of Serena and Venus Williams, is kind of the other end of

the extreme. Like it's not that he's the world's best parent, but in terms of, you know, getting achievement out of his kids, he was a very unusual parent. He devoted his entire life to making tennis stars out of them. They were very talented to begin with, and if they hadn't been, he wouldn't have been able to do what he did. But most kids, there are probably tons of other young women out there who have the talent that Venus and Serena had, but their parents weren't like these extremes. Their parents weren't willing to chuck everything

and devote their lives to tennis around the clock. Well, I bet a lot of parents who just heard you say about what you said about good enough parenting is like a big relief. It's like, oh, God, thank God, you know, because you always think you could have done better. And but you're saying that that's not having as big an influence on your kid as you think it is. I think if there's one takeaway, it's that you are it's that most parents are not having as big of an influence as they think they are. We agonize over these decisions.

Should we have a chore chart? Should we co-sleep? Should we let them cry it out? Should we be strict? And it's at the end of the day. It's not as make or break as we think it is. Now, what does matter, I would argue, is how your kid feels in the day to day moment in your home, you know, do they feel that you care about them? Do they feel that

you are setting appropriate limits? Do they feel safe? Do they feel that you're consistent? You know, so it's not that like the parenting decisions that you make are inconsequential for your child's life. Of course they are. It's just that you don't have to feel responsible for whether your kid is valedictorian or not. I would say relieve yourself of a little bit of that pressure. We're talking about how kids, how people turn out the way they do.

Susan Dominus is my guest. She's author of the book book The Family Dynamic, a journey into the mystery of sibling success. Hi, I'm Adam Gitwitz, host of Grim, Grimmer, Grimist. On every episode, we tell a grim fairy tale. Not the cute, sweet versions of the fairy tales that your children have heard so many times. No, we tell the real Grim fairy tales. They're funny, they're weird. Sometimes they're a little bit scary.

But don't worry, we rate every episode grim, grimmer, or grimist. So you, your child, your family can choose the episode that's the right level of scary for you. Tune in to Grim, Grimmer, Grimist, and our new season, available now. I'm Amy Nicholson, the film critic for the LA Times. Grimmer, Grimmest, and a case you missed them. We're talking Parasite the Home Alone. From Grease to the Dark Knight. So if you love movies like we do,

come along on our cinematic adventure. Listen to Unspooled wherever you get your podcasts. And don't forget to hit the follow button. So Susan, I'm curious about the effect siblings have on each other, and I'm sure it depends a lot on how close they are. And a lot of siblings are far apart in age or don't get along well. So maybe they don't have.

So there's probably a lot of variability. But I'm curious, because I suspect siblings can have quite an impact. The way I often talk about it is to say that parenting effects are probably overestimated by the general population, because we think it's the be all and end all. And sibling effects are probably overestimated by the general population because we think it's the be all and end all. And sibling effects are probably underestimated

because there's just really not that much. There's just shockingly little research about how siblings affect each other in general. Now part of that is that siblings are hard to study. There's half siblings, there's step siblings, there's different age gaps among them, there's different gender configurations. So it can be, it has been very challenging to study it effectively, but researchers are starting

to find interesting ways to figure out, you know, how much do siblings affect each other, and how much is just, you know, to the extent that they are similar, how much of that is because of maybe a genetic overlap, or because they are being parented the same way. And so there's this one study that I find really fascinating because it gets around those confounds. What this researcher did was look at school start dates. We know that kids who go to school a little bit old for their grade,

just by virtue of when their birthday falls, those kids, especially I should say in disadvantaged communities, do better academically than kids who are younger. It's just if you're older for your grade, you're gonna be a little bit more developmentally advanced. That means you're a little bit easier in the classroom. The teacher likes you a little bit better.

Things just go a little bit better for you, and then you have a positive feeling about school. You're more cognitively mature. So it's, we know that kids who are old for their grade do better, and that's kind of a random element, right? Like did you happen to be born at the right time for that to be possible? When you look at the younger siblings of those kids,

they also do better than would necessarily be anticipated. And that's true regardless of when their birthday is. So that's how you know that it's having a sibling who had this lucky break that makes the difference for the other sibling who is just, you know, not necessarily old for the grade. It's a true sibling spillover effect. It's not parenting that's making it happen

and it's not the genetics. It's just this one random element of, did you happen to have a birthday that made the older sibling a little bit older than his or her peers in the classroom? Is there any research that would show that siblings who are close influence each other more than siblings who are less close? Is the relationship of siblings

impactful? So what I would say we know is that in disadvantaged families the sibling effects tend to be stronger and one reason for that it doesn't necessarily speak to whether the siblings are more emotionally close, but they tend to spend more time together because maybe their parents are working long hours, or they don't invest as much in extracurricular. So it's not like one kid is out, you know, rock climbing, you know, all afternoon while the other one is practicing oboe, you know, the kids are kind of hanging around the house a little bit more when there are fewer resources to spend on extracurriculars. So those kids do have more of a sibling spillover effect. I think when siblings are close and they collaborate, they can have this incredible network effect that allows them all to

do better than they would if they were operating independently. But I will also say that sometimes you can see siblings in whom there is this rivalry. And people think that everyone's trying to please their parents. It might have nothing to do with the parents. Sometimes having a sibling who you want to best, perhaps because there is tension there,

can be extremely motivating. I mean, this is anecdotal. But in my book, I do write about tension there, can be extremely motivating. I mean, this is anecdotal, but in my book, I do write about this family, the Groffs, and Lauren Groff is this tremendous novelist, bestselling, award-winning. She has an older brother who she felt always patronized her a little bit, and it created this fury in her to show her worth

and show him up, I think, basically. And she told me at one point, and by this, and she was by then like a mother and a very accomplished author. And she said that 90% of what motivated her was this sort of feeling she had towards her brother. I mean, quite an extraordinary thing to say. So I think sibling dynamics are complicated.

They are messy. They can work in all kinds of different directions. And we're just trying to understand what some of the consistent patterns are. You've talked about how the oldest child often has a cognitive advantage, an academic advantage over the other children, but is there any research that shows that younger children have an advantage somewhere else? There's good research that finds that younger siblings are overrepresented in elite sports and that they also, if you look at all the entering freshmen in a class who played varsity

sports in high school, more of those kids are younger siblings as well. And the idea is that the oldest kid does well academically and the younger kid says, all right, I'm going to pick a different lane. I know I can excel in this. does well academically and the younger kid says, all right, I'm going to pick a different lane. I know I can excel in this. Where does the only child fit in this discussion? I'm not aware of any research to suggest that it's like damaging to be an only child. You know, it's true that they lack the kind of network effects that strong sibling groups

have with each other, but they have something else, which is they have all of the, if you think about the oldest child having this academic edge because their parents poured all this enrichment to them, even just for a couple of years, think about how much that's gonna do for an only child over the course of an entire life, right? Like, and it's not just that they have all the parents'

attention and enrichment efforts being focused on them, course of an entire life, right? And it's not just that they have all the parents' attention and enrichment efforts being focused on them. They also have all of the parents' financial resources. And so much of what affects our quality of life, frankly, is what economic opportunities do we have. After looking at all this research, what other conclusions can you come to? I mean, I think that consistently I found that when parents know their kids well and they treat them like individuals, you're going to get better results.

So it's about setting expectations for your child that are consistent with who your child is. You can't just say, I had one mother say to me, I don't understand. I set really high expectations for both of my children and only one lived up to them. Maybe your second child, you know, is not destined to be the valedictorian in the class.

Not everybody is. And so when parents set expectations that are inappropriately high for a given child, not only can it be demotivating for that kid, but we also know that it can be linked to high rates of anxiety and depression. What about the idea that parents today are just too involved with their kids and that's not doing them any good? When I look at these high achieving families, I do see the parents really encouraging their kids to believe that they're tough, to believe they can do it. They let them take risks, even when it was

scary. I mean, Marilyn Holofield, who went on to become the first black female partner at a law firm, a major law firm in Florida, she ran an influential boycott. She's just this extraordinary woman. She was the one who told her parents when she was 15 that she wanted to be one of the first kids to desegregate a high school in in Tallahassee. And I'm sure her parents knew it would be awful, but she was hell bent on doing it because it was the best high school in Tallahassee and she wanted access to the best high school. And they let her do it. And they never tried to twist her arm into quitting, even when things got really, really tough.

I think there's language that a cognitive psychologist once used with my family when we were helping one of our kids who was struggling with something. And she said that we just needed to say to him when he didn't want to do something because it made him anxious, hey, you're tougher than you think, you can handle this. And, you know, you're tougher than you think is very much an implied message that I saw in a lot of the families. And that really became extremely

useful language for us. I love that. You're tougher than you think. You're tougher than you think, yes. And you say it in a very Mary Poppins-like, cheerful and assertive tone without overdoing it. And kids are tougher than they think. Lisa D'Amour is a really well-respected child psychologist who's written several best-selling books. She believes that parents are too afraid of their children's anxiety and that makes the kids afraid of anxiety. Nervousness, anxiousness, these are normal healthy responses before you head into a game with a team

that you know is gonna kick your butt. It is normal to go into a solo at a concert feeling nervous, that's okay. It's not something that means you have to then avoid altogether so that you don't have that uncomfortable feeling. No, that's a healthy feeling and you're gonna survive it. And you know what, if you screw up the solo,

you're gonna survive that too. It's okay, you're tougher than you think. Well, this is a topic that I think everyone thinks about, either about themselves, how did I turn out the way I did or my kids or my siblings, how did we come to be who we are? It's great to get some insight into it. I've been speaking with Susan Dominus. She is a writer who's been at the New York Times for several years, and she is author of a book called

The Family Dynamic, a Journey into the Mystery of Sibling Success. There's a link to her book at Amazon in the show notes. Susan, thank you for being here. Mike, thank you so much. I've really enjoyed talking to you. From the podcast that brought you to each of the last lesbian bars in the country

and back in time through the sapphic history that shaped them comes a brand new season of Cruising Beyond the Bars. This is your host, Sarah Gabrielli, and I've spent the past year interviewing history-making lesbians and queer folks about all kinds of queer spaces, from bookstores to farms to line dancing and much more. You can listen to Cruising on Apple Podcasts, Spotify, or wherever you get your podcasts.

New episodes air every other Tuesday starting February 4th. Humans are not perfect. I'm not talking about not perfect in the sense that we make mistakes or make bad choices. I'm talking about biology. So humans have been around for a long time. So one might think that by now, over that time, evolution, survival of the fittest and all that would have weeded out the flaws, the diseases, the genetic imperfections by now.

But we have a fairly high rate of genetic diseases compared to other species. So why aren't we closer to genetic perfection than we are? And will we ever get there? That's what Lawrence Hurst is here to talk about. Lawrence is a professor of evolutionary genetics in the Milner Center for Evolution at the University of Bath. He's author of the book, The Evolution of Imperfection, the Science of Why We Aren't

and Can't Be Perfect. Hi, Lawrence. Welcome. Glad to have you on something you should know. Lovely to be here. So let's begin with an example of what you mean by we're not perfect genetically. One of the things that has been discovered over the last few years, for example, is that about half of all fertilized eggs, so the very earliest embryos, half of those will

die. In humans? In humans. But if we do exactly the same experiment in fish, for example, the answer is none. They're all fine. So, it's a funny human thing. And again, if we look at human pregnancy, about 5% of human pregnancies will end in a condition called preeclampsia, where the mother's blood pressure goes sky high.

And this can kill the mother and the baby. So, it turns out it's one of the great kill the mother and the baby. So it turns out is one of the great killers of mothers and babies globally and the odd thing about this particular condition is it's only seen in humans. So it's a human specific but lethal condition of pregnancy and there are many other sort of similar genetical issues where they just leave you scratching your head going why are we so bad? Did you know for example that we've got one of the highest mutation rates? So when parents get together to make kids usually the kids DNA is a simply a copy

of the parents DNA but they we all have new mutations so a little error somewhere in the DNA and we've got one of the highest rates of all species in these errors. And one of the consequences of this is that we have a very high rate of so-called genetic diseases, or rare genetic diseases. So a rare genetic disease is one that affects less than one in two thousand of us, but about five percent of us have a rare genetic disease. They're not that rare and that's because humans are odd. We've got a very high mutation rate. What are some examples of these rare diseases you talk about?

Oh, there's loads of them. Some of the haemophilias, for example, these bleeding conditions, these are quite commonly due to a new mutation in part of the system that makes sure that when you cut yourself you don't bleed for example. Hemophilia A, hemophilia B would be some of the more common ones. So that's the sort of thing that we're talking about. They're not common, but you may well have heard of some of them, but they are particularly common in humans. So when you say mutations mutations you mean that when two people get together and have a baby they create this baby and rather than the baby being just a

copy of the genetics from the parents something changes? Yep absolutely you can think of it as a bit like you've got a data file on your computer and you're transferring it over to, I don't know, you're making a copy of it and you're transferring it over to a USB stick. This is a bit like parents copying their DNA, giving it to the kids. What's happening in the process is occasionally mistakes are made. So just as occasionally that file can end up having not quite the right instructions or rather not the original instructions you

might say, so too when mum and dad make copies of their DNA to give to their kids there are differences made because of that copying process. So we're all born with about 50 or so of these new mutations, changes to the DNA. More if your father is old, less if your father is young. Do we know why that happens in humans and why it happens less in other species? Well, we do indeed. And so this is one of the themes of a body of theory that I think is not particularly well known. It's called the nearly neutral theory. What it says is that this classical process of natural

selection, the survival of the fittest, that is not so efficient when populations are small. Typically what we think natural selection should do is keep the mutation rate really low. Now, why is that? Well, it's because organisms are actually well-functioning things. And if I were to give you my lovely watch, for example, and you were just a tinker with it,

you're more likely to break my watch and get me very angry. Likewise, if you go to a really well-functioning engine of a car and you just randomly change something, then you're more likely to break the engine of the car. And the same is true of DNA and mutations. So mutations are like random tinkering of the engine or the Swiss watch, you're more likely to break it. So then the question is, why do we have a greater mutation that's three orders of magnitude higher than some other things? And that's where this other theory comes in.

It says actually that selection to keep the mutation rate down is inefficient if populations are small. So our problem in having a high mutation rate is because we evolved when we didn't have a very large number of us. We think there were about eight to 10,000 of us. And evolutionarily speaking, that that's very very small population. Are there a lot of mutations that get passed down that are fairly benign and what I mean by that is as I understand it some time ago there was a mutation and somebody for the very

first time was born with blue eyes. And then that person had children who had children who had children who also had blue eyes. But blue eyes, although it's something that's very obvious, you see it, but it doesn't really have much effect. In other words, being born with blue eyes doesn't change your life a whole lot, doesn't ruin your life, doesn't change your life a whole lot, doesn't ruin your life, doesn't kill you. It's a mutation, but with no real consequence. So there are some sort of, yeah, obvious ones that may well be largely irrelevant in terms

of your ability to survive and reproduce and leave kids and so on and so forth. But the great majority of mutations probably have absolutely no effect whatsoever, or almost no effect whatsoever. They almost all will have some tiny, tiny, tiny effect, but not one that you can physically see. So that's because most of our DNA appears to be relatively pointless. There's this sort of magical 10%, which is not pointless,

that if you have an effect in there, you will see some deleterious effect probably most of it yeah you change it and it has no effect. Do the mutations so when my parents had me and there were there were mutations? Yep about between 10 and 100 or so yep you are unique we're all unique. Okay so when have children, is it possible for those mutations to stop with me or will I automatically pass them on to my children? You will not necessarily pass them on. So there's two processes we have to think about here.

One is what we call purifying selection. So imagine there was a mutation and it kills you. Yes. Before you got to reproduce. That is good old, what we call purifying selection. That mutation came into the population, it killed you, it's gone out again. You will not be transmitting to any kids

because you will not have any kids. So that's selection. There's another process, which is just simply chance. So you got two copies of your DNA, but the mutation will only have been in one of them. Typically the DNA two copies of your DNA, but the mutation will only have been in one of them. Typically the DNA you get from your dad, we get many more mutations from dad than we do from mum. But it's quite possible that when you transmit your DNA to your kids, they got your version that you got from your mum and not the version that

you got from your dad. So there you are giving on the unmutated version, just simply the version that you got from mum, not the mutated version that you got from dad. You do get a few mutations from mum, just not as many. So yes, it is possible that you have mutations, you simply don't transmit them, not because they're bad mutations, but simply because in effect they're unlucky mutations. Your kids only have half your DNA and so you flip a coin as it were and half the time you flip the coin and they don't get mutation half the time they will get the mutation. Is what you said about large populations and small populations the reason why other animals you know know, flies, mosquitoes, whatever, you know, where there's zillions of them, is that why they don't have these problems?

Absolutely. That's why we think this is the case. In the last 10 or so years, we've been able to work out what the mutation rate is for lots and lots of different organisms. And we can do this because we can basically work out the DNA of mum, we can work out the DNA of dad, we can work out the DNA of the kids. And then it's a spot the difference competition. Yeah. So you go, where are the kids DNA different from mum or dad's DNA? And we go, okay, you must have got a new mutation. And so we can work out what's the rate at which that's going on. And the answer is that if you're in a population

of mosquitoes, the rate at which that is going on per unit of DNA is about an order of magnitude lower than the rate at which it's going on in us. But yeah, they've got a lower rate. And it turns out that the mutation rate very nicely scales that we can now know with how many individuals are there in a population. Lots of individuals in the population and the mutation rate is low, few individuals

in the population and the mutation rate is high. Well what's a lot? I mean we have several billion people on the planet. We have several billion now. We did not have several billion when we evolved. So as I said, if we go back to before the modern expansion of humans, which is 20,000 years ago or so, we estimate that there were about 8,000 or so of us, which isn't many.

And that's pretty normal for a primate of our sort of body size. So the other predictor of this is just how big is your body. So whales have a low rate like us. They got very big bodies and very small population sizes likewise elephants and so on and so forth So yeah, the things with large ish bodies evolutionary speaking comparing cross-organisms. We've got a large body So there are they were historically very relatively few of us And the consequence of that is that when we were evolving we were much more prone to chance events. So help me understand this something I

I've never been clear on. If I got cancer it might be or people would say, it could be hereditary, but it could also be a mutation. And a mutation doesn't necessarily bring the disease with it, it creates the disease when it mutates. Is that correct? Cancer is complex and in many regards what you said is absolutely spot on. So if you look at something like breast cancer, for example, about 5% of breast cancers are highly heritable. So if your mother had breast cancer and her mother had breast cancer, we can now sequencing up your DNA and go,

okay, you've got a mutation and then you can do what Angela Jolieela Joly did, for example, go, I likely will get breast cancer. And so there you have a key mutation that is really tilting the balance towards you getting cancer. Many other cancers are not like that. There may be weaker genetic predispositions,

but many cancers rely simply on bad luck. That in your body, the cells are dividing all the time, they're mutating all the time, and you could just get unlucky. You may have no predisposition genetic-wise towards cancer, but because those cells are dividing all the time, they're mutating all the time, you could just be simply unlucky and develop cancer within your body. And at the moment, because people are living quite long, we estimate that about one in two people will get cancer sometime in their lifetime. It isn't necessarily because they inherited genes for cancer. They could have inherited some weaker disposition

or they could inherit, as with these 5% of breast cancers, very strong predispositions. Those very strong predispositions are such that you only really need one other mutation and you will get cancer. For the others, you need a handful of mutations, a lucky combination, and you will get cancer. But yes, you can inherit predispositions to getting cancer, but a lot of cancer is simply bad luck. So, how close are we to being able to find mutations and go in there and tinker and fix them? Great question. So this is really the most exciting age in many regards because what we can now do is sequence DNA.

So every one of us has about three billion base pairs of DNA. That's quite a lot in every one of our cells, actually two copies of DNA. There's quite a lot in every one of ourselves, actually two copies of that, and we can now work out exactly what that looks like for each each and every one of us. And in principle we can then go and go, okay you've got this condition, whatever that condition may be, and go, oh we found what the problem is. You've got this mutation in this gene here. And we can do that now ultra fast and ultra cheap. So let me give you some really, I think, interesting and fantastic figures. So when the human genome

was first sequenced, all that DNA from one individual was sequenced, it cost three billion dollars. It took about 15 years. We can now do exactly the same for around $100 and it takes an afternoon. So because of this you can now go to your doctor and the doctor goes I think you've got a genetic condition. Sequence up the DNA, now look at it and go right there we think is the problem. So there are cases now where for example example, a kid goes into hospitals screaming their heads head off, awful headache, very young kid. And in this case, the doctors decided the kid almost certainly had a genetic disease, sequenced the DNA, worked out what the problem is, worked out what the cure was, and that

was two and a half days. So this is a revolution in medicine. In that particular case it turns out it was a problem with importing a particular vitamin into the cells. It was a B vitamin that couldn't go into the cells so a diet could fix it. What's particularly exciting at the moment is there's a different sort of fix to these genetic problems and that different sort of fix is called gene therapy. So for example with hemophilias but also with sickle cell anemia which is very common in for example the African American community in America at the moment. But with hemophilias for example we know what the

mutation is. So you've got a gene it's making a protein that's not working right, and so your blood isn't clotting properly. You bang your head, you will probably die. Currently the best we can do is give you synthetic versions or give you blood transfusions. So the idea behind gene therapy is to say, no, those are all just sticking plasters. What you really need is the right version of the gene to make the right version of the RNA to make the right version of the protein. And so we can give you the gene. And that in a very profound sense is a cure. But this is a gene that goes into your body to make, allow you to make the missing protein that allows you to clot your blood properly. It doesn't go to your offspring because it's only going to affect the cells of your body but not the cells of sperm or

eggs. And likewise with something like sickle cell anemia we can take out your bone marrow, engineer the bone marrow genetically by giving it the right gene, putting it back again and you now can be effectively cured of sickle cell disease. It is a cure, you're taking a mutated gene and you're giving the better version of the gene, the one that most other people would have, and that then is working absolutely fine. But there are all sorts of problems with it. It's not a pleasant process to have this done and there is mortality along the route. So the first gene therapy trials had to be stopped, for example, because it turned out

that the intervention itself was causing down-staining problems, it was actually causing cancer. Some of the next ones had to be stopped because the way of delivering the gene, it turned out caused a massive immune response in the poor individual concerned and they died. So it's been a very slow birth but we think we're overcoming a lot of these technical hurdles and most particularly safety hurdles and so I suspect it's something that we will hear a lot more about in the not too distant future. Well I suspect everyone has wondered you know why do we have cancer and other genetic illnesses and why can't we get rid of them and I

appreciate the explanation and it sounds like anyway that there is promising future in medicine that will address this whole issue. I've been speaking with Lawrence Hurst. He is a professor of evolutionary genetics and author of the book The Evolution of Imperfection, The Science of Why We Aren't and Can't Be Perfect and there's a link to his book in the show notes. Thank you, Professor. I appreciate the explanation. Thank you very much. It's been a real pleasure. Your kitchen has a way of attracting clutter that you probably don't even notice. So the editors at delish.com have some advice

to get rid of the clutter, starting with a really easy one, the real estate agent and pizza delivery magnets on the fridge. They can go. Then there's your plastic container collection. Empty food storage containers take up a lot of space in the kitchen. The recommendation is to limit yourself to two sizes of reusable containers, five to six pieces

in each size, and that way you're not fighting to find the right lid for each bowl. Coffee mugs. They just seem to multiply and pile up. Most people don't need more than six coffee mugs. The rest can go. Anything that came for free with your dinner. Spare chopsticks, soy sauce packets, kids meal toys. You're always going to get more the next time you order, so there is no point in stockpiling. Barely used cookbooks.

If you've owned a cookbook for over a year and haven't made a single thing from it It's probably time to consider selling it unless it's a family heirloom in which case you could just move it to the living room Pots pans or skillets. There's a pretty good chance if you look where you keep your pots and pans and skillets and things There's a few in there that you never use. I can't remember the last time you used it. So why do you keep it? Those recipes you're saving for some day. If you print it out or tore out of a magazine a recipe more than a month ago and you haven't made it yet, you're not gonna make it. So you might as well just get rid of them and that's okay. And that is something you should know.

A great way to show your support for this podcast is to leave a rating and review on whatever platform you listen on. Apple Podcasts, Spotify, most all of them have a way to leave a rating and review and they help us and we appreciate it. I'm Mike Carruthers. Thanks for listening today to Something You Should Know.