Instant Genius - The genetic evolution and future of humankind

Episode Date: November 8, 2024

Understanding who we are and where we came from is one of the most fascinating questions in science. But it’s also one of the most difficult to answer. Putting all of the pieces together requires research across several different disciplines such as genetics, anthropology and medicine. In this episode, we catch up with Professor of Human Genetics and Evolution at College de France in Paris Lluis Quintana-Murci to talk about his latest book Human Peoples: On the Genetic Traces of Human Evolution Migration and Adaptation. He tells us how the characteristics of different human populations have been shaped by the environments they live in, how our genes can protect us against disease and what we learn can from all of this about our future health and wellbeing. Learn more about your ad choices. Visit podcastchoices.com/adchoices

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world-leading scientists and experts talking about the most fascinating ideas, in science and technology today. I'm Jason Goodyear, commissioning editor at BBC Science Focus. Understanding who we are and where we came from is one of the most fascinating questions in all of science. But it's also one of the most difficult to answer. Putting all of the pieces together requires research

across several different disciplines, such as genetics, anthropology, and medicine. In this episode, we catch up with Professor of Human Genetics and Evolution at College de France in Paris, Luis Kintana Mercy, to talk about his latest book, Human Peoples, on the genetic traces of human evolution, migration and adaptation. He tells us how the characteristics of different human populations have been shaped by the environments they live in,

how our genes can protect us against disease, and what we can learn from all this about our future health and well-being. Welcome to the podcast. Thanks very much for joining us. Thank you. Happy to be here. So today we're talking about your new book. Human peoples on the genetic traces of human evolution, migration and adaptation. So as a first question, what's the premise of the book? Well, the premise of the book basically, okay, let me tell you what's the book not about.

The book is not only about the use of DNA to understand our origins. The book is not only about the use of DNA to understand migrations. adaptations to the environment. What's novel of this book is that it put all this together and the premise could be less understand and dissect our past to better understand who we are today in the present and eventually better envisage the future. So in the book you say the sort of general framework of our knowledge about all of this is Darwin. So let's get everyone up to speed. You know, what is that and why is it such a powerful idea? Charles Darwin proposed the theory of natural selection. Basically, to make it very graphic

and very understandable, if a giraffe have a longer neck, the giraffe will be advantage towards other that have shorter necks to eat the leaves of a given tree. So if this could, trade that is to have a longer neck is heritable, then after some generations there will be many giraff with longer necks. This is the theory of natural selection. And the strength of that is that today we can dissect through the study of our genomes, which are the genes and which are the mutations that have participated in making us what we are today, you and me, the descendants of those who survive in the past. So you've mentioned there a few terms, DNA, genetics, genomes, etc.

So let's get those out of the way first then. So what's the difference between a gene, a genome, and then you also talk about population genomics. So can we explain those terms, please? Yeah. So basically a gene is a fragment in our DNA that encodes for a protein. For example, we have a gene that is a piece of DNA, and this gene, after some processing that I'm not going to get into details, will be translated into an enzyme, which is a molecule that will allow us to digest milk, for example. This is a gene. A genome is the collection of all these genes in our DNA. Our genome, our genome,

is made of 3 billion letters, GATC. That's the genome. So how about population genetics then? Where does that come in? Population genetics is an old discipline based on mathematics, on statistics and on biology, and basically is the study of the distribution of genetic diversity between, between populations. And through the study of the genetic diversity of different populations and why this given mutation is at higher frequency in population A and at lower frequency in population B, we can study migration patterns at mixture that is the mixing between two populations, but also natural selection. So let's rewind a little bit then. So we humans,

are scientifically known as Homo sapiens, but there were many other human-like species that we've discovered that lived and are related to us in the past. So how do we make those distinctions? Well, these distinctions can be made based on anthropology by comparing, for example, the skulls of Homo sapiens and Neanderthals, but also can be made on the basis of genetics. Why?

because we can sequence the genome of a human, a homo sapiens, and thanks to the advancements in the sequencing of ancient DNA from fossil remains, which is a revolution over the last 10 years, we can also sequence the DNA, the genome, of a neanderthal. We can then compare the two genomes and using some sophisticated population genetics, what we call in jargon the molecular clock, we can know how long ago these two sequences diverge. And in this case, when this was done in the community, they saw that Neanderthal

and Homocipian's genomes diverge around 600,000 years ago. So how similar are those two genomes? Well, they're super similar. Like 99. something percent, they're all similar. But because we diverge from an evolutionary point of view recently. Consider that in evolution, 600,000 years ago, is yesterday. No one goes to Hank's first spreadsheets. They go for a darn good pizza. Lately, though, the shop's been quiet.

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Visit focal powered by name.com for more information. So in the book, you often talk about this idea of admixtures. So what do you mean by that? Admixture is the term we use in population genetics to refer when two populations interbreed, mix with each other. We are all at mixed to different extent. You have entire continents, like from Mexico's south. Almost all populations are at mixed between the Native American, autotoxinous genetic background, who, for unfortunate reasons, that is colonialism, admixed

with the European background that came in the last 400 years, and for even more unfortunate reasons that admixed with the African ancestry that came during transatlantic slave trade. These are kind of extremes of a mixture, but even in Europe. that we look so similar to each other. Just Europeans, including British people and Irish, we are the result of four different genetic components that had mixed it with one another. The first hunter-gatherers that came from Africa

around 50,000 years ago, who had mixed it with Neanderthals. We'll come back to that, probably. But then these populations in Europe admixed 10,000 years ago with farmers that came from Anatolia, present-day Turkey, and brought farming to Europe. And these populations admixt it again around 4,000 years ago with another group of people that they were called the Yamaya culture that came from the eastern steps, and most likely, brought to Europe, Indo-European language, that most of us we speak today. So let's talk about other migrations then. So you mentioned there it's quite a short amount of time that this has happened. So what effect has that had on the migrant's physiology?

Well, this is a great question that is the essence of my book. Because as humans, in just since our ancestors left Africa, around 60,000 years ago, we have spread everywhere in the world and we have been able to live in very diverse and extreme climatic conditions in hospital lands of the Arctic Pole in regions of extreme hot and humidity like the rainforest. Humans can even live in conditions of hypoxia, meaning low oxygen concentrations, like people living in Tibet, at 3,000 meters above the sea level, the levels of oxygen are 40% less. So there's humans everywhere. So your question is, how have we succeed in being able to live everywhere? So, obviously, leaving apart cultural adaptations, like the invention of clothing to protect

ourselves from cold, or the introduction of antibiotics and vaccines in the beginning of the 20th century to fight infectious diseases, genomics, that is the study of the genomes of different populations, has provided remarkable examples of how, during this, journey around the globe, our ancestors were able to biologically adapt to very different climates, to very different nutritional resources and to even different pathogens. Yeah, so you mentioned there people that live at high altitudes. So you mentioned Tibet, but there's some places in the Americas that are the same. Is there any correspondence between those two? Yes and no, which is beautiful.

It's a beautiful why, because the adaptation to high-altitude, low oxygen in Tibet and in South America in Diandes, has been achieved through mutations in different genes and different pathways, which is a beautiful example of convergent evolution, meaning through different evolutionary trajectories we are reaching the same final objective, being able to live in extreme conditions of low oxygen concentration. So how about, so I'm very, very pale, and quite clearly northern European. So how have I evolved, or my ancestors, you know, why do I look like this? So you look like this, a bit like me. I might be slightly more tan than you because I'm from southern Europe. But our ancestors lost pigmentation.

For a long time, people thought that our ancestors lost their pigmentation just because they could allow to do so. In other words, because not living in Africa in such conditions of UV light, some mutations appear that made our ancestor to lose some pigmentation, and that was tolerated. because UV light was not so strong, so we didn't have to be so much protected. But again, genomics and population genetics in particular has showed that this was not an incident. This was something that was strongly advantages, was positive selection.

Losing skin pigmentation in northern latitudes like Europe was something that our ancestors went through because in regions of low UV light, you need to lose pigmentation in order to keep on synthesizing enough levels of vitamin D that is photosynthesized in the skin thanks to UV light. So you mentioned earlier things like the immune system and drugs. And in the book, you talk about our relationship with microbes and other organisms. So what role has that played?

Don't forget that 99% of our history as humans, we have been constantly dying of infection. Microbes like viruses like bacteria, viruses like flu, bacteria like mycobacterium tuberculosis, which causes tuberculosis, or parasites like plasmodium, which causes malaria, have been with us since. ever. Let me give you an example of how massively strong has been the pressure imposed by pathogens on our survival. In the UK, in the end of the 19th century, in Liverpool in particular, just 38% of the population reached the age of 40. Today in the UK, 98% of the population reached the age of 40. So this is thanks to all what happened in the end of the 19th century and the beginning of the 20th century that this improved hygiene, antibiotics and vaccines. But this long story to tell you that during most of our history we have been dying of infection, reason by which the genes in our genomes that are today involved in immune responses to pathogens show among,

the strongest signatures of adaptation, of natural selection. Yeah, so sort of sticking with migration, it's often said that when the conquistadors went over to the new world, they took with the infections that the population weren't accustomed to, and that just spread rapidly through the population. So one, is that true? And two, how did that happen? Well, one is that true? Yes, most likely. This is a true. This is what has been documented on the basis of history, which I'm not an expert of. I'm an expert in genetics,

and I can tell you that there is ongoing studies using ancient DNA, meaning DNA extracted from fossil remains, comparing Native American populations pre-contact and post-contact, and showing how this has altered the genetic diversity of their immune genes, which supports from a genetic, point of view that the arrival of Europeans to the Americas was not only an intended genocide in some cases because of war, but also an unintended, with lots of brackets, genocide in terms of the pathogens Europeans brought to the Americas, to which Native Americans were not adapted

to. Yeah, so sort of moving on from that slightly, so you talk about something called the polygenetic risk score. So what is that and what can it tell us? Polygenic risk scores are that the cases which I mention extensively in the book of a mutation allowing you and me and 40 to 60% of Europeans to digest milk in adulthood. A mutation in another gene that has participated in our ancestor and losing skin pigmentation. Or, mutations associated with adaptation to low-oxygen concentration are the exception rather than the rule. In most cases, our phenotypic variation, meaning being taller or shorter, this is in health, but also in disease, meaning being more or less resistant to COVID-19. this is in most cases due to many genes with different mutations

and each mutation having a tiny effect in you and me being taller or shorter. But the hundreds of mutations together in a additive way will make that you are taller than me, for example. Polygenic risk scores are scores that will predict on the basis of genetics, your risk to develop crown disease, Alzheimer disease, or SARS-Co-2 infection. So in the book, you talk about this massive treasure trove, I suppose, of information called the biobank. So what is that? And why is it so important? Well, biobanks in the UK, you have the beautiful example of the UK Biobank that was pioneer in the world in doing that.

Biobanks are, what are they? Biobanks are simply a collection of biological material for hundreds or thousands of individuals. The idea is that you take thousands of individuals from the UK and then you extract, for example, from their saliva or their blood, their DNA, but also you have medical records for each of them, which allowed them to correlate, to associate how genetic variation affect disease risk. But I want to say something important here. We are not the box of genes. We are not just the product of our genome.

And what's very important, and in the UK Biobank, there's many studies showing that, is that, of course, our genomes and our specific genetic makeup of each of us can make us more susceptible to develop breast cancer or to have obesity, for example. But, of course, there's other differences that participate in that. Being a biological male or a biological female, being younger or being older, eating very unhealthy, or eating trash food. So in the very end, all this together is what will make you more or less susceptible to a given disease. And this is the final

objective of biobanks. And the final, final, final objective of biobanks is to put the basis of precision medicine, personalized medicine. What does it mean this? Means if we accumulate information of thousands or even hundreds of thousands of individuals, from whom we have their genomes sequence, they are males, they are females, they are younger, they are older. We have very precise medical questioners, lifestyle patterns if they smoke, how much they drink alcohol, their nutritional habits. And we put all this together. Eventually, we will be able to predict which are the factors that make that you are more or less susceptible to a given disease. And I would say even more importantly, if we put all this information together, we can train models based in

AI, for example, in order to predict how you are going to react to this particular drug. So what I want to emphasize, and I think this is the strong premise of my book, It's again, let's dissect using population genetics our past migrations at mixture patterns and adaptation to understand who we are today. We are the descendants of the survivors. And let's use all this genetic information, we are the products of our past, together with lifestyle parameters, to train models and that all this genetic and non-genetic information can be useful for health, for the society and to predict our reaction to some therapeutic treatments. Yeah, so of course, this is what you call admixture is an ongoing process.

You know, so what can we say about that? Listen, when two populations meet, there's three different scenarios. One scenario is that they keep on being neighbors, but they don't admit mixed. Basically, they do not make love and they do not have children, right? Just to be clear. Second scenario is that one population replaced the other, usually as a result of a conflict. The third scenario is that the two populations are mixed. Genetics research for the last 15 years

show that the rule is that when two populations meet each other, often they mix. So I think we have to stop seeing different populations in the world, like hermetic boxes, and we have to start to integrate what we really are as a species. we are a meta population made of different populations that exchange culturally,

move spascially and mixed biologically. Thank you for listening to this episode of Instant Genius, brought to you from the team behind BBC Science Focus. That was Professor Luis Scintana Mercy. To find out more about the topics we've just discussed, check out his latest book, Human Peoples, on the Genetic Traceous, of human evolution, migration and adaptation.

If you liked what you just heard, then please do consider subscribing to InstaGenius on your preferred podcast platform. The current issue of BBC Science Focus magazine is out now. Pick up a copy wherever you buy your favourite magazines or downloaders on your app store of choice. You can also find us online at sciencefocus.com. This podcast is sponsored by name, audio and focal.

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