Instant Genius - Everything that's wrong with the human body

Episode Date: June 13, 2018

We like to think of ourselves as highly evolved, well-adapted creatures, but our retinas face backwards, we have too many bones in our wrists, and at least half our genome is junk. Biologist Nathan Lents explains what we can learn from our flaws. Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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for their environment. No, it definitely does not do that. Evolution and natural selection really leave us with just good enough to survive, and that's about it. We are not evolved to be healthy, to be happy, to be comfortable, right? We're just evolved enough to make the best use we can of our resources. Get us to reproductive age. You're listening to the Science Focus podcast from the BBC Focus magazine team.

We're the UK's best-selling science and technology monthly, available in print and in several digital formats throughout the world. Find out more at ScienceFocus.com or look out for us in your app store. Hello and welcome to the Science Focus podcast. I'm Alexander McNamara. the editor of ScienceFocus.com. We humans like to think of ourselves as highly evolved creatures, but we're far from perfect.

For example, our genome is half junk, and our sinuses would drain better if we hung upside down. In fact, we seem to have more of these errors than most of the animal kingdom. But as biologist Nathan Lentz is here to tell us, our flaws are interesting and informative. He's outlined our shortcomings and explained why we should appreciate them in his new book, Human Errors, a panorama of our glitches from pointless bones to broken genes.

Here he is speaking to BBC Focus editorial assistant Helen Glennie. The book is about the human body and a little bit about the human mind and why we have examples of suboptimal design. Let's put it that way. In other words, some things in our body and mind just don't work very well, just don't work right, don't work as well as we would expect. And certainly with most of the examples I use, don't work as well as we see other animals working.

because and these have all of these examples of flaws and glitches have really interesting backstories that explain a lot about why we are the way we are and and i often say it this way if you spot something in the human body that just doesn't seem right there's probably a really interesting story there but but my book is in some way a reaction to this this perception that a lot of people have to expect perfection in nature And, you know, creationism has, you know, long been pushed aside in favor of modern biological theory. No one takes creationism seriously anymore. But there's a couple of leftovers from creationism that still permeate, even the scientific community.

One of those is the expectation of perfection to see, wow, you know, evolution, natural selection creates organisms that are perfectly adapted for their environment. No, it definitely does not do that. Evolution and natural selection really leave us with just good enough to survive, and that's about it. We are not evolved to be healthy, to be happy, to be comfortable. We're just evolved enough to make the best use we can of our resources, get us to reproductive age, and that's really about it. So we're not evolved to be perfect. The other thing that's sort of the leftover of creationism that really colors our thought is this idea of human exceptionalism, that humans are the pinnacle of creation, the top of the evolutionary. ladder, all of these weird metaphors that make no sense biologically. And we know that,

you know, if we were to answer like a quiz, we would get the answers right about this, but it's still almost like a subconscious thing where we really think that humans must be the prime example, you know, the exemplar of perfection. But they actually, in many ways, we have a huge brain, all right, more cognitive power than every other species. But really, that's about as far as our exceptionalism goes. And in fact, I argue in the book that we have probably more flaws than most other species do because we were basically able to outsmart our environment in a certain extent. So our body didn't need to be perfect because we had these big brains. We could compensate for weaknesses in the body and still survive.

But also the big brain allowed us to have a social structure which involved what we called division of labor and different ways that people can live and survive. and thrive and contribute. So that means that whatever your imperfection was, you just do something else. So if you don't see very well, well, okay, you can be a homesteader. You know, you can contribute to the success of the group in a different way. So I think we've had the pressure off of our bodies to be optimal for a very long time. It's not just modern sort of civilization that has taken natural selection out of the picture, which it mostly has.

but actually this goes back further than that. And so we're not quite, I think we're the product of what you would expect to see when you don't have a lot of pressure on the body to perform optimally well. So what kind of flaws are we talking about here? Can you give us some examples? So, you know, I talk about the anatomical flaws. Those are, I start the book with those because those are the ones that almost everybody can relate to. The one that seems to be getting the most attention from reader,

right now is a flaw that we have in our sinus cavity. So we have several sets of paired sinus cavities, but the biggest one right here is called the maxillary sinus cavity, really behind your cheekbones. So this has one drain spout in most of us, and it's at the top of the chamber, not at the bottom, the top of the chamber. And what that means is that our cilia,

these little hair-like structures in the chamber, have to work very hard to push, the mucus up, right? So it works against gravity all day, every day, as long as we're standing, and push the, push the mucus upwards in order for it to drain down into the regular drainage route. Well, that's fine and good when you're reasonably healthy and there's not a lot of dust and allergens and things like that. But it does not take much in our mucus before the mucus gets too thick and viscous, and our silo just simply can't keep up. So it cannot propel the mucous upwards when it gets really thick and full of stuff. And what happens? We get a cold,

we get a sinus infection. And you don't have to look very far. Find another species that gets cold symptoms as often as humans. You won't be able to do it. Even livestock, which have these very unsanitary conditions, they don't deal with sinus infections and just the common cold as often as we do. because we have these really, really poorly designed maxillary sinus cavities, and they don't drain properly most of the time. And also, the drainage spots are really, really thin. So it doesn't take much to get them clogged. Now, that by itself is frustrating, of course, anybody who's had a cold.

I mean, you have pets, right? You have dogs and cats. Do you ever see them sniffling and sneezing and dealing with these cold six or eight times a year? Of course not. They don't, they don't, it's really, I've had a dog for seven years. I've never once seen a runny nose. So it has a consequence. But the interesting thing, the story's not it.

That's not the end of the story. If that were it, this book would be, I think, would be kind of boring. But what does that tell us that we have this weird science cavity? Well, what it tells us, and we can look at other mammals for this. So mammals, most mammals, and in fact all ancient mammals have long snouts. So they're a snouted species. That's the sort of the default mammal facial. arrangement. And why do we have long snows, huge nasal cavities? Why? To concentrate all these

olfactory receptors. Because mammals, early mammals anyway, were driven by this sense of smell. That was their key way of navigating the world. And your dog is a perfect example of this. Their smell is so, is millions of times better than ours. It's just incredible. Well, what happened in the evolution of primates and then later the evolution of apes is the snout got smushed in. It got reduced because instead of relying on smell, we started relying on vision. And the eyes came towards the front to give us what's called binocular three-dimensional vision. So most of our visual field we see with both eyes at the same time and we can create a three-dimensional space out of that. So we're much more reliant on vision than we are in smell. And getting the nose out of the way

helped with our vision too. You have this big snout. It's blocking your view. So we reduced the snout, brought the eyes forward. But what happened is all these sinus cavities just got all shmushed up. And other primates and other apes have dealt with that problem in different ways. orangutans simply ditched some of their sinus cavities to make room. Chimpanzees, gorillas, they all dealt with in a different way. Humans are the worst. It's just bad luck that we end up smushing the cavity this way with the drainage pipe up at the top. But think about how poor of an arrangement that is. I mean, what plumber puts the drain pipe at the bottom of a chamber? I mean, at the top of the chamber, right?

You put the drain at the bottom because gravity can help you flow. So, but why didn't we fix it? Because the common cold doesn't kill you. So you don't take this poor arrangement with you in death. Instead, you know, we sniffle our way through life. Now, I also will admit that it probably wasn't near the problem that it is now for most of our evolutionary past, just because we weren't living at really high population densities. So we weren't passing around cold viruses the way we are now.

But we still definitely had symptoms. There's just no way because you can get these symptoms even in a dusty environment. It doesn't have to be an infectious agent that causes this drain problem. And anybody with allergies will know that sometimes it feels like the world's out to get them. But they don't die of it, right? Food allergies may be. And I do cover those two in the book. But environmental allergies and other nasal symptoms, they just don't kill you very often.

So that's kind of in evolution's blind spot. is one way to put it. Most of the human design flaws that you described fall into one of three categories. So can you just explain those three categories? Okay. Well, one is that we are living in a world that's very different than the world that we evolved in. So it kind of like a mismatch, right? Where we probably were well designed for a different kind of life.

Right. So, you know, in the Pleistocene epoch in sub-Saharan Africa, some of these things made great sense, especially around our diet. Our diet might have been a good example of that. You know, we are built to tolerate the kind of food that we were eating at that time, but we don't eat that anymore. So it's a mismatch between what we're designed for and how we're actually living. A second category be what we call compromises. So evolution doesn't work by magic, right? It works by little tweaks and tugs with the body that we already have.

We very rarely invent whole new structures. That's a really rare thing. When it happens, it's usually a whole new kind of animal. So tetrapods, you know, evolving from fish. That's, I mean, a quintessential moment does not happen very often. For the most part, we have to just co-opt the little things that we have and do tweaks and tugs. So flight, we'll say, wings and flight is invented several times. But when it happens, the creatures didn't grow wings out of their back.

So when bats or birds or taradactyl, so let's take those three, all three separately evolved, they lost their forelims. Their four limbs instead of doing this became wings. So that's an enormous compromise because you can't grasp, you can't do all the things that you can normally do with your forelimbs. And that's a great story about how evolution works. It takes the body you have and makes tweets and tugs. So they gained flight, they gained wings, but they lost the ability to do other things with their forelimbs. So that's the second category. Compromises, tradeoffs, sort of design tradeoffs that have to be made when you're balancing multiple factors.

The third category, that's what I call just the flaws. Just nothing gained, no compromise, no, it was better in the past, just an outright. There's no explanation. So we almost have the ability to make vitamin C. for ourselves like most animals do. So vitamin C is called a scorbic acid. The reason it's a vitamin why it has the name vitamin is that we lost our ability to make it. We lost one enzyme that was necessary to make it. So now we need it in our diet. So it's important in our diet. But our liver used to make it in our deep past. And in fact, most animals, like your dog doesn't need vitamin C. You don't have to

feed fruit to your dog. Your dog doesn't need any vitamin C because her liver. makes the vitamin C that she needs, like most animals do, duh, but ours doesn't. Why? Because some ancestor of ours, who was the, turned out to be the founder of the group that we know as primates, mutated their gene called Gulo, El-Gulano lactone oxidase, Gulo, is the name of this gene, got mutated. And so we can't make vitamin C. We can almost make vitamin C because just one enzyme in the synthesis of vitamin C got mutated. We can almost. make it, but we can't. We have the gene, but it's broken. It's a broken down version of the gene. We didn't gain anything from that. It was just a freak mutation, and through the pure

randomness of chance, that individual happened to be the founding member of what would become the most dominant mammal of all, the primates. Why didn't it kill that animal? When you lose such an important thing like vitamin C, that animal should have gotten scurvy and die. Why not? Because they were in Africa. Africa. There's citrus fruit. There's other sources of vitamin C all around. So the body just didn't notice. Here we are now stuck with this as a dietary requirement. And that's why, by the way, primates have not gone to every single climate around the planet. They are stuck to climates where vitamin C is present. And in fact, Europe is the best example. There were no primates

in Europe ever until Neanderthals and then later humans came. And when they came, they suffered from scurvy a lot. Scurvy was a huge public health concern before we figured out how to not get it. And to this day, the only primate that is native to Europe is humans. The one exception, outside of zoos, humans are the only primates. One exception, though, one exception, which I find very interesting, is the Barbary macaques have migrated via boat from Morocco to Gibraltar and through to southern Spain. So there's a very small community of Barbary Macacaques living on the southern border of Spain and in Gibraltar. But they are probably eating dates from human cultivars.

So they're getting access to vitamin C that way. But the problem is so this vitamin C thing, nothing gained. It's just a pure flaw. There's a chapter in the book about junk in the genome and eras in our genes. Can you tell me a little bit about what you saw there? First of all, we have genes that are what are called pseudogenes, sometimes called broken. genes, and that's in the title of the book, which are mutated beyond repair. They have no function. They don't express anything. Some of them express something non-helpful or non-functional, but they're

mutated. It's a junkyard. And we have so many of these. We have tens of thousands of these of completely useless genes that either used to function in important ways, and we've lost that function or they've become duplicated in some way or they're the so back when they were functioning we got duplicated copies and so when you lost one it didn't matter so either way we have a bunch of just junk but we do tofully copy and proofread and do all this work around these non-functional genes so it's it's like a junkyard that someone goes around and waxes the cars in this junkyard i mean why do we do that um the other thing is that we do have sequences that are what we call purely competitive that are self-copying and self-maintaining.

And these are basically parasitic DNA elements that are dedicated only to their own copying and proliferation. They don't do anything, or at least they don't do you anything useful. And in fact, they can actually cause a great deal of harm. And I list a whole bunch of genetic diseases that clearly have their origin from one of these repetitive sequences smashing into the gene and destroying its function. So there's, I mean, many countless millions of people have died because of these jumping DNAs that go around the genome and wreak havoc.

Luckily, over evolutionary time, they tend to quiet down and slowly become dormant. And in fact, there's one thing called the Allu element, A-L-U-A-L-U, that we have over a million copies of this stupid little repetitive sequence, a million copies in your genome, of this purely repetitive parasitic DNA that, fortunately, has finally stopped. But it's been around. I mean, this thing dates back to what a group called the super primate. So this is even before the origin of primate.

So we're talking hundreds of millions of years here. And it took that long to quiet the thing down so it's not hurting us anymore. Although every once in a while you get a happy accident. So sometimes these things do their bit. And I have one story in there where our ability to see the rich colors that we can see. We have a richer palette of colors that we can see than most other. primates, and that's come, I should say primates have it that most non-primates don't, that's come through one of these sort of jumping DNAs. So every once in a while you get lucky,

but the phenomenon itself, you have, like I said, you have tons of these. So I don't know what the percentage of your genome is that is purely non-functional because that number changes, but it's definitely more than half. There's no way it could ever be less than half. most people who really study this would put it around 75% of your genome is not helpful in any way. We would be better off without that 75%. So that's a lot. Yeah, so presumably we still don't understand everything about what our genes do. So how do you tell the difference between segments that are useless junk DNA

and areas that we just haven't discovered a function for yet? That's a fascinating question. And I think even the way we phrase the question tends to change from decade to decade. There was one project that got a lot of press called the Encode Project. It was, God, millions, maybe billions of dollars spent on this. And they defined function as if the gene ever expresses anything. And let me tell you, that's the dumbest way to define function. It really is.

It is really not a smart way to define function because you can accidentally express things. And you can express things like these parasitic DNA that's harmful. And in fact, a guy I know wrote an article called the I Is. immortality of TV sets. And his article basically just really destroys that definition because they found accidental expression and all kinds of crazy places in the genome. And then they called it functional. And by the way, that project is no more.

So there's no one to even respond to these criticisms. But the better definition, I think, of a functional piece of DNA. And Dan Grower at University of Houston has pioneered this definition is something that can be mutated. in other words, something that can't have a loss of function. So if a mutation has some cost, then it's doing something. If a mutation has no cost, then it's not doing something. And I'm over simplifying it a little bit, but basically if it's subject, and the way he would put it is if it's subject to natural selection.

So if it's evolutionary, then it has a function. And he has done some really fancy mathematical work about what's called mutational load to estimate that 25% of the genome is important to function. Where are we headed as a species? Will we ever eliminate these errors? Have we reached a stopping point now where this is what we're stuck with? Well, I don't know that we'll be fixing most of the errors I talk about in the book in a genetic way anytime soon.

It's not even foreseeable. And I'll give you an analogy. I think that genetic fixing, genetic engineering... of humans will proceed first with genetic diseases, simple genetic diseases. We're basically there already. We have the technology. It's just a matter of how do we tool it safely? Because if you take cystic fibrosis or hemophilia or sicklea or single cell anemia,

there's a few diseases, not many, but a few that have what are called simple genetic diseases, where there's one gene that we have to go in and fix, and that's it. Everything else I'm talking about in my book, we don't even know the genes to start with. So the knee, you asked about the ACL. We don't know which genes to fix to create a stronger ACL. We don't have the first beginning. And I guarantee it won't be one. It will be tons of them.

And we don't know what effect it will have to tweak those, what other bad effects will have all over the body. Because most genes don't just do one thing. They do tons of things all over your body. And so our ability to, first of all, we don't even. know the genes for the ACL. We don't know which genes cooperate. It's probably hundreds of them. We don't know what else those genes do. So we are so far from being able to sort of tailor-make our bodies. And I think most people who are worried about the use of this genetic engineering, because CRISPR, the CRISPR-Cast-9 technology has made gene editing very easy, very fast, very easy. But what it can't do

is tell us what to fix. And like I said, there's no substantive. for the slow boat in understanding how a gene actually creates an organism. So if you want to design a better need genetically, genetically, we are, it is nowhere in sight. We have no clue what to do to do that. Now, I think the frontiers of medicine will be to fix things in our bodies that are already wrong. So we accept that we're stuck with the genetics that we have for the most part, but then once we're born, we can start tweaking things with, you know, sort of nanotechnology and stem cells and going in and recreating things that way. But that would have to be redone on every person. I don't think we're going to fix us genetics until we pass any of that stuff on

or so that we have designer babies in the womb or anything like that. I just think that that's most people that that are worried about that aren't geneticists because a geneticist would tell you that no, we don't have any of the knowledge we need. I mean, even something as simple as eye color, we're just really figuring out all the genes. And it is multiple. genes, right? It's not a single gene. But something as simple as eye color is a multigenic trait. It's a polygenic trait. So there's many genes that we would have to fix. And those genes do other things in the body that we might not be prepared to deal with, you know, the sudden problems that that would create. So I just don't think that we're anywhere close to these, you

know, sculpted, all tall, beautiful sculpted bodies with keen minds and all of that. I just don't think we're anywhere close to that. So we wouldn't even know where to begin. Okay, so we've talked a little bit about where we're headed in terms of evolution through technology. What about evolution through natural selection? Is that even taking place anymore in humans? So natural selection in sort of in the classic sense of the word, doesn't really apply to humans for the most part. Very few individuals who are born, don't make it to reproductive age. Very few.

The vast majority of individuals who are born will live to reproductive age. Now, that's only part of the story, though. Natural selection is only one of the evolutionary forces. There are many other evolutionary forces. We're introducing a very interesting evolutionary force, which is choice. We choose whether or not we're going to reproduce or not. And a lot of people, especially in the more economically developed countries, are choosing not to reproduce or to reproduce and have one child, two at the most.

If someone has three kids nowadays in the West, we say, wow, three kids. It's like, oh, but there are countries where 10 and 15 kids are not uncommon. And certainly in our past, I mean, I was the fifth child in my family, and that's almost unheard of now. I have two kids, and I sometimes complain to my mother. I'm like, oh, there's two of them. And my mom's like, do you really think I have sympathy for you? But anyway, the point is that reproduction is not random, right? So certain people, certain groups are reproducing way less than other groups. If you take Japan, Japan has very, very low birth rates.

Italy also has very, very low birth rates. But countries like Afghanistan have sky high birth rates. So they're contributing more to the gene pool of the next generation than the Japanese are in terms of the numbers. So that means the population does change over time. So we are evolving, but just not really through natural selection. So natural selection seems to be off the table right now for most people. So you found a lot of human errors for this book. Can you just tell me about a few of the ones that you found the most fascinating?

Here's an interesting one. So vitamin B12 is an essential vitamin. Cobalman is what it's called. you absolutely need this in your diet. You eventually would suffer and die potentially if you didn't have any of it in your diet. It's essential. Well, we pretty much can only get it from animal sources, right? Meat, fish, milk, have some of it in their eggs.

So if it's essential and we can't live without it, how the hell do all of the herbivore animals do it? So you've got cows and the vast majority of animals are herbivores. They don't need any meat, and yet they don't have any trouble with vitamin B12. What's bad about us that we need this in our diet? So it turns out we have bacteria. All animals have bacteria that make vitamin B12 for us, and they serve it right up to us, right in our intestines. Our intestines have these bugs, these bacteria that makes the B12 for us.

It's a byproduct. I mean, they're not doing it to be nice, but they make it, we use it. Everything's fine, and that's how. all the herbivore animals do it. Why isn't that good enough for us? This just baffles me. The bacteria that make b12 are in our large intestine, but we can only absorb b12 in our small intestine. So it's bad plumbing strikes again. So the place that we absorb it is upstream of the flow of traffic in the place where it actually gets produced for us. So we eliminate. So we actually do make tons of vitamin B12? We don't, but the bacteria do. And instead of absorbing it, we send it to the

toilet. That's where all the vitamin B12 in your gut goes to is to the toilet rather to you. And I just, it doesn't get much more stark than that. And, you know, people who are vegans, well, most vegans are aware that they do have to worry about vitamin B12. That's sort of one of the few things that vegans have to really be careful about is that if they don't get B12, they're going to get anemia, macrosidic anemia. But the, a lot of soy milk, gets supplemented with B12 just for that reason, because soy milk is a staple for vegans and just as a public health measure, they just throw the B12 in. We supplement regular milk with, I should say, cow's milk with vitamin A and D for the same reason.

So, yeah, I mean, that's just one of these things. Like, how could it be? How could it be? Yeah, it comes across us just incredibly tragic. It's not that we don't produce it. It's just producing the wrong place. The wrong place. That's right.

And we don't absorb it. And actually, our vitamins, we have a lot, we have a pretty needy diet overall. You know, and it's when you're navigating a healthy diet, doesn't it seem a little obnoxious? Like, you need a little bit of this, little bit of that, not too much of that. And, you know, other animals, you feed your dog the same staple every day. My dog is a lamb and rice dog food. And lamb and rice is all my dog eats and he's perfectly fine. Humans really are persnickety with our diet, with our dietary needs.

And I look at the koala bears, the other example, who of course is not a bear, but koalas, they eat eucalyptus leaves, and that's all they eat pretty much. Or at least that's all they need to eat. They can be totally healthy eating nothing but eucalyptus leaves. We could never do that. There's not a single food we could eat that we would be okay if we only ate that. And why is that? well, we evolved in basically a salad bowl, is one way to put it. We had a lot of rich and nutritious foods. Now, getting to it isn't always an issue, and we certainly had droughts and famines and meat

came in huge supplies very rarely, but you know, you'd have a big kill and you'd have a lot of meat for a few days, and then you'd have nothing for weeks. But that's the problem. When our body got used to, a little bit of this, a little bit of that, became reliant on. a little bit of this, a little bit of that. So what sounds like a good thing, oh, we're omnivores, we can survive in all different kinds of foods. And it is a good thing.

But the drawback is our body's got used to being fed a lot of different things. So now you need that. You really do need a varied diet in order to be healthy. You can't just eat the same thing all the time. One thing I want to emphasize is that it's not a depressing tale.

The story of our flaws in imperfections is really, it's uplifting. And my point in writing this book is not that our body is terrible. My point is that our body has a past and it has an interesting past. And the more we learn about the past, the more we can live in concert with our own biology. So if we want to explore our biology, we can't concentrate only on the good stuff. We have to concentrate on our weakest parts because that's the area where you can improve things. So if you want to live in harmony with your body, you have to understand its flaws and its past. So

I think it's a fun book to raise, an uplifting book. That was Nathan Lentz talking about our biological imperfections. His book, Human Errors, is available from Orion Books now. Tune in next week, when Jason Goodyear speaks to material scientist, Marks Mier Dovnik, about the growing problem of plastic waste, what we should be doing about it, and why plastic isn't always bad for the planet. Did you enjoy this podcast? If you liked what you heard, then why not subscribe and leave us a review?

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