Rowan: really, it goes deep. Once you start pulling at the threads of this tapestry, takes you into all different places.

Rebecca Nesbit: Hello and welcome to Cat Among the Penguins. I'm Rebecca Nesbitt.

Jenny: and I'm Jenny Hickman. Today we're going to be discussing the question of does it matter that we're part Neanderthal? So for those of you who have been keeping up with the series, you may have seen Becky get very excited about the idea back in episode three. were having very existential conversations about why we're protecting nature. And it was an idea that Becky got really, really excited about and wanted to do a full episode on. So here we are. So modern humans interbred with Neanderthals, meaning genes from an extinct species live on in us. We found this a very humbling thought and we think it can help reframe the way that we think about both ourselves and nature conservation.

Rebecca Nesbit: And following on from our existential thoughts on episode three, again, this is more of a conceptual episode and it's based on our discussions, but we do have some clips from other people, including a very special guest. I interviewed new scientists Ron Hooper for an upcoming episode about malaria extinction, and it just so happened that he had really relevant things to say.

Jenny: I'm excited. I'm looking forward to it.

Rebecca Nesbit: You'll be even more excited when you hear what he has to say. But I'm pleased to say this is also connected to our last episode where we talked about genetic purity and free living honeybees. We heard from Dr. John Ellis then, and he likewise saw connections with this episode, so I've got some clips from him for you as well.

Jenny: Amazing. So we've got a lot to talk about this episode and we're pretty excited to do it. But just before we we've made it now to our sixth episode. So we wanted to say a really, really big thank you to everyone who has listened and supported us so far. It's been really, really great. Please, if you haven't already, please click like, subscribe, on whatever platform you are listening to us or watching us on. We really, really appreciate the support and it's really helping us to grow the podcast. So huge thanks to everyone that supported us so far.

Rebecca Nesbit: We really appreciate it. Whatever level of Neanderthal you have in your genes.

Jenny: Okay, so let's start with some of the basics. some of the stuff that I needed clarifying for this episode is let's talk a little bit first of all about who were the Neanderthals? So Neanderthals are our closest relative. Neanderthals and modern humans evolved from a common ancestor somewhere between 700 and 300,000 years ago. they're generally stockier than modern humans. They had shorter limbs and broader joints. and their faces were very, very distinctive. So they had very thick brow ridges, unlike our much kind of flatter faces. They never had a big population, but they did have a very wide distribution in Southern Europe and Western Asia. And they went extinct around about 40,000 years ago.

Rebecca Nesbit: for much of Neanderthal's history, Homo sapiens were living in Africa. So the two species weren't encountering each other. But humans left Africa, moved into Europe and Asia, and that's when the two species started to overlap in their range. So from a About fifty-four thousand years ago, humans and Neanderthals were interbreeding. So how much Neanderthal DNA you have in you depends on where you come from. For people whose recent origin is outside Africa, an average of one to four percent of their genome is inherited from Neanderthal ancestors, and the highest levels are found in people of East Asian origin.

Jenny: super weird to think that there's a person in my family tree that was half Neanderthal.

Rebecca Nesbit: Yeah, and there is a a Neanderthal in your family tree. And interestingly, this it is

Jenny: Yeah, that's weird.

Rebecca Nesbit: weird, and interestingly, this could have been happening really quite regularly. Some analysis of genomes of three early humans found in Bulgaria showed that they all had Neanderthal ancestors just a few generations back. And likewise, genome sequencing from a fossilized jawbone of an early human in Romania. showed that between eight to eleven percent of their DNA was Neanderthal. And to put that into context, everyone on average shares 12.5% of their DNA with each of their great grandparents. And I remember two of my great grandparents. It can't have been very many generations back that these specimens had Neanderthal ancestors, which I think is interesting because it it breaks certain taboos in our culture. I don't know whether this is partly because Western culture has a very Judeo-Christian outlook of species being neat categories and humans being separate from nature, superior to other life forms. So the idea, particularly that humans are interbreeding with another species. I think is quite weird for us.

Jenny: And think definitely one of the big reasons why we kind of wanted to do this episode right. goes back to episode three when we looked at intrinsic value and where that lies and we talked about what is a species and what defines a species. Species are not neat categories and if humans are certainly not a neat category species or we wouldn't have interbred with other species.

Rebecca Nesbit: And this wasn't an isolated incident. It wasn't even just Neanderthals that we were interbreeding with. The genomes of present-day people with ancestry in Oceania and eastern parts of Asia also contained genetic sequences from Denisovans. This is another hominin group named after the cave in Siberia where the first skeleton was found. Denisovans are cousins of the Neanderthals, and the two split. Sometime around four hundred to five hundred thousand years ago.

Jenny: Yes, so it's thought that Neanderthals, archaic homo sapiens and Denisovans evolved from a common ancestor, I'm going to try and get this right, called Homo heidelbergensis. Hopefully my pronunciation's right there.

Rebecca Nesbit: Sounded good to me.

Jenny: I'm sure we'll get told if it's not. And those three species all came together in modern homo sapiens. And so this kind of gradual splitting of one... common ancestor into three species shows how we wouldn't expect species to be in E categories. They didn't suddenly evolve from Homo heidelbergensis into the next species in a single generation.

Rebecca Nesbit: there's also variations within a species. So in the Denisovans, for example, there were multiple groups. So it's not just that Denisovan was one smooth species, there were different groups within that.

Jenny: So yeah, to get back to the question of does it even matter that we're partly anaphyl, part of that is whether or how it's impacted human evolution. So was there benefits to us breeding with these other species?

Rebecca Nesbit: Well, fortunately for us, John from episode five is an evolutionary biologist and this is what he had to say.

Jonathan: a genetic ancestry test online and found that I have more Neanderthal variants than the average person. And, you know, the fact that those variants have persisted in the human population for so long shows that you can get what you call adaptive introgression. So the variants that were introduced from Neanderthals into humans have persisted. been maintained by selection.

Rebecca Nesbit: Anyone watching on YouTube will notice that John has quite red hair. And interestingly, it seems that we've got Neanderthal DNA that's related to blue eyes and blonde or red hair. And in fact, a stretch of Neanderthal DNA related to skin pigmentation and freckling is found in about 70 % of Europeans. So having some Neanderthal genetics could have facilitated human adaptation to new environments when humans spread into Europe and Asia. They will have encountered different climatic conditions, different UV exposure levels, and new pathogens. And interbreeding with Neanderthals could have helped them adapt. And it's still relevant today, if we take the example of a gene inherited from Denisovans, this helps regulate the body's response to low oxygen levels, giving Tibetans a physiological advantage in the high altitudes of the Tibetan Plateau.

Jenny: super interesting it's a really really cool story and I just wanted to clarify that John mentions in his clip that these genes were maintained by selection which is kind of the process in which specific traits are favoured that will provide some kind of survival advantage rather than just kind of random genetic changes over time. But how can we know how can we be sure that this Neanderthal DNA has been maintained by selection because it was beneficial and not just by random chance?

Rebecca Nesbit: It's a good question, but one piece of evidence is that Neanderthal DNA isn't spread evenly across the genome, There's actually some parts of the genome where Neanderthal DNA has been lost, suggesting that it's been selected against in those locations. One example is that Neanderthal DNA is pretty absent from an area on chromosome 7, which encompasses the forkhead box protein P2. And that's a gene involved in speech and language. And interestingly, the areas of the genome that have less Denisovan DNA from people in Oceania overlap with the areas lacking Neanderthal DNA in the genomes of Europeans. So that's further evidence for selection causing some of these genes from other species to be lost and others retained.

Jenny: Yeah, and of course what that actually looks like in the real world in practical terms is that offspring will have had to die for those genes to have been lost along the way. Nature's pretty harsh, right?

Rebecca Nesbit: Yeah, nature is very, very harsh. it does also show the power of evolution that change isn't always a bad thing. In this situation, change was good. It allowed the humans to thrive.

Jenny: Yeah, for sure. And I think we can sometimes there's a bit of a tendency to be really resistant of change in conservation, whereas actually, you know, changing genetics allows species to adapt to new environments, new climates. So it's actually really important in times like changing climates and climate change.

Rebecca Nesbit: And that very much connects with what our guests, John and Ollie said about changing honeybee genetics in the free flying bee episode, because the Western honeybee is a very genetically diverse species. So I'm going to play you another clip from John, but just to give you a bit of context that again, another species defying the idea of species neat categories, Western honeybee. comes in lots of separate subspecies. So these can very easily interbreed, but they are genetically different. And because scientists weren't satisfied with defining them in terms of species and then subspecies, they also had an intermediate category of lineages. So these are groups of subspecies that are more genetically similar. So in Europe, we have both lineage and C lineage bees, and these lineages can interbreed. here's what John had to say.

Jonathan: the case that when there's introgression from different honeybee lineages, let's say C into some of those variants are adapted for the population and will be maintained by selection into the future. And some level of mixing of genetic backgrounds by gene flow and then maintenance or elimination of those variants by natural selection would be part of what goes on naturally in populations, but it's the massive extent gene flow that's the issue really I think today with the scale of imports is so enormous.

Jenny: Essentially what John is saying here is that gene flow between different groups and subspecies is natural and very important for adaptations. in the past, these lineages would have been a lot more isolated and a lot more separate. But now due to how much we're moving bees around, there's a much bigger amount of gene flow than would have naturally been happening. And that can be both good and bad. So I think we often focus on these kind of ideological ideas of genetic purity, but actually what's important here is the kind of practicalities of what impact gene flow has.

Rebecca Nesbit: Exactly. So John isn't talking about any ideology, but about what it means for the bees, good and bad. And I think this very much brings us back to episode three, where we talked about what is the intrinsic value of nature? Where does that intrinsic value lie? because to make practical decisions about when interbreeding between species and populations is good, when it's bad. We need to know what our ultimate goal is.

Jenny: And often at the moment, our goal is to adapt to a very changeable environment. So genetics are never optimal and as environments change, our genomes may actually be maladaptive. So what does this mean for our original questions? In practical terms, does it matter to us that we're part Neanderthal?

Rebecca Nesbit: Well, it seems that it does in that some Neanderthal genetics are not good for us now. One example is a Neanderthal variant that increases blood coagulation. It could have helped our ancestors cope with new pathogens that they encountered as they moved into Europe and Asia by sealing wounds more quickly and preventing pathogens from entering the body. But in modern environments, this variant has become detrimental because this hypercoagulation increases the risk for diseases such as stroke and can increase pregnancy complications. Also, a genomic segment inherited from Neanderthals seems to be a genetic risk factor for severe symptoms after COVID infection and hospitalization. and a specific bit of Neanderthal DNA significantly increases the risk of nicotine addiction and a number of Neanderthal variants influence the risk for depression, some positively and some negatively.

Jenny: Yeah, and I suppose that it just kind of really shows us that human evolution can't keep up with such a changing environment. So we're sort of maladapted almost to the modern world, which is really to be expected because in evolutionary terms, the andesles went extinct 40,000 years ago, which is actually the blink of an eye for a species like humans who have fairly long generation time. So if looking at the average reproductive age of 27 in humans, There's only actually been around 1500 generations of humans since Neanderthals went extinct. So if you compare that to how quickly our environment can change just in our lifetime, how quickly our environment has changed, then it makes complete sense that genetics that were beneficial back then might actually very quickly become redundant and possibly even harmful in a new environment.

Rebecca Nesbit: yeah, absolutely. Evolution is definitely not perfect in any context, let alone when the environments that we're exposed to have just changed so rapidly. But at the same time, the evolution that was happening on the plains of Africa, and when we were interbreeding with other species in Eurasia, has set us up for modern life in some amazing ways. For example, we're so adaptable to all sorts of situations and tasks. We didn't evolve to be able to set up a microphone and make a podcast, the environments we were exposed to and our skills to adapt allowed us also to adapt to this totally different and amazing new world.

Jenny: Yeah, and also as far as I understand it, also, have a lot of other species to thank for this as well. So it's not just Neanderthals and Denisovans, but we also, I believe we have viral DNA in us. Apparently it's 8 % of our genome comes from viral DNA.

Rebecca Nesbit: which is just mad, isn't it? It's not exactly that our ancestors were breeding with viruses, these are retroviruses like HIV. So they insert DNA into the host's genome. And most of the time, like HIV, this can't be passed down between generations, but a few viruses have infected germline cells. So these are the sperm and the egg that allow... the DNA from the virus to become inherited. And this was happening far off in our evolutionary past, and a lot of this DNA has gradually mutated over time. So some are genes making proteins, but most of this is in what we used to call junk DNA because we didn't know what it did. Now we know that just because it doesn't code for genes doesn't mean it isn't fundamental. And this is what's turning genes on and off. So I've got exactly the same DNA in the skin of my finger as in the neurons of my brain. The difference between them is caused by which genes are turned on and which genes are turned off. And so it's this extra DNA that is allowing that to be possible. And we've got viruses to thank for some of that.

Jenny: It's so fascinating, so fascinating. it's also not unique to humans. So viral DNA dates back millions of years, way before homo sapiens, when species we evolved from were infected with viruses. So it's also present in other animals. And it's actually this viral DNA has played a really, really crucial role in evolution. So one gene derived from a virus plays an important role in the formation of placenta. and pregnancy in mammals is dependent on this virus derived DNA. And even, not even just mammals, but also some reptiles. Mibua lizard in the Andes mountains of Columbia gives birth to live young. And this is possible because they have advanced placentas just like ours. And again, this is thanks to viruses entering their genomes.

Rebecca Nesbit: viral DNA is also involved in our immune responses against disease. But of course, like Neanderthal DNA, it's not all good. there's still a lot we don't understand about this, but when DNA sequences originating from viruses are expressed in the brain, This seems to contribute to susceptibility for some psychiatric disorders such as schizophrenia, bipolar disorder, and depression. So there's still people studying the connection between viral genetic sequences and disease. There's a lot we don't know, but there seems to be very interesting connections there. And I'm sure over the coming years, we'll start to unpick more of that.

Jenny: Yeah, it's amazing to think of that. And of all the things that you think are going to be kind of impacting your mood, you don't expect it to be virus DNA. I think there's also some really important lessons here to talk about our interconnectedness. So you said earlier that there's been this very long standing idea of humans as this kind of superior species. So very different from and separate to the rest of nature. But this just shows us that this is not the case at all. Everything about us has kind of been shaped by this sort of mosaic of influences from species that live around us and with us and alongside us and right down to our genetics. But it doesn't. it doesn't stop at our genetics. Our health and moods aren't just affected by DNA we inherited from extinct species, but also by species that live around us today. We're actually still a part of this ecosystem.

Rebecca Nesbit: We really are and sometimes this is in very obvious ways and it really affects my mood on a short time scale. This week I've been watching all the bumblebees, the moths on my lavender and it does boost your mood. Plus of course my health depends on so many species that make my food, the worms that impact the soil fertility, insect pollinators, fruit trees. And in my case, the yeast that makes my Marmite is very important.

Jenny: and inside us as well. So there's a whole ecosystem inside us. The microbes inside us affect our moods in ways that we don't notice or appreciate. So we ourselves are also an ecosystem. Our bodies can't function without our microbiome and the microorganisms that live on us, inside us, around us. All of it is symbiosis.

Rebecca Nesbit: Yeah, such an incredible symbiosis. And I think when I was researching for my book, Tickets for the Ark, that connection between our moods and microbes was one of the most mind blowing things. I actually spoke to new scientist Rowan Hooper about this, and he had recently published a book togetherness with the tagline, Symbiosis and the hidden story of life's greatest collaborations. And this is what he had to say.

Rowan: one thing that really struck me during writing the book is that we all know about serotonin, that sort of mood chemical that is produced in our bodies that makes us feel good. But 95 % of that is made by the bacteria in our bodies, not by human cells, it's made by bacterial cells. So our moods... our very mood is impacted, is not just impacted, created by our microbiome. So, you know, it's not just how we digest food, it's how we feel, how we think. So, we're so tightly integrated with other species. And yet that's not been acknowledged at all, like on a personal level, but also on a much broader conservation level, as you say.

Jenny: That's so incredible. There's definitely a reason that the gut is referred to as the second brain. So I think we drastically underestimate the importance of the gut microbiome. And an unhealthy gut is now thought to be connected not only to very obvious issues such as obesity or gut and bowel issues, but even mental health conditions such as anxiety and depression and potentially even things like asthma. So keeping these little guys happy is about so much more than we realize.

Rebecca Nesbit: I mean, is there any better conservation scheme than caring for the bacteria that live on you and in you? But this is just so different to a lot of the narratives we hear. And actually, if we think back to Darwin and the version of evolution we learnt at school, it's all about competition and survival of the fittest. But actually natural selection has created a natural world that's full of connectedness and symbiosis. this is very much what Rowan explores in Togetherness, he explores how the natural world has been forged and sustained by small miracles of cooperation, which I think is a beautiful way of putting it.

Jenny: a really beautiful way putting it. I love that so much. And he's right, symbiosis was one of the big driving forces of evolution. So it was only when single cells started cooperating through endosymbiosis, where a big cell literally would engulf a little cell, not to digest it, but to work together in a partnership. And that was actually how complex life forms evolved. So symbiosis is fundamental. to all ecosystems, but we completely ignore it.

Rebecca Nesbit: Yeah, certainly Rowan worries that by neglecting symbiosis, we inadvertently damage that symbiosis and we've started to undermine ecosystem function all around the world. So he had some really important points to share about our place in these ecosystems.

Rowan: But the message of togetherness is about understanding that ecosystems are these complex, living networks, but crucially that we are part of them, that we don't exist, you know, like a sort of Attenborough show that we just see on TV and we go, look, isn't that beautiful? Look, there's nature over there. everyone loves watching those shows, but what we've got to understand is we don't just look at nature as something over there. It's here, it's part of us all. And what we think of as us being individuals, we've got to start to understand that we're not, we are not just individuals. We can't go out and exploit nature like we have been doing for hundreds of years, and it's been getting worse and worse in recent decades to the point that many ecosystems have got to the point of to collapse. So it's about really, really redressing the balance, the idea of understanding that we are absolutely part of nature and it's not in some hippy-dippy way, it's in a very critical way to the way the whole of our planet functions. And so the book is really at its basis is trying to get that point over that we are really part of nature and we've got to turn this around as fast as we can.

Rebecca Nesbit: What Rowan says there really resonates with me. We are part of nature. And the fact that humans interbred with Neanderthals is just a reminder of how true that is. I think this has a lot of implications for conservation. We evolved as part of nature. It's not somehow unnatural for us to change other parts of nature, change the ecosystem that we are part of. conservation often has ideas of wanting to return to a baseline when somehow nature was superior because it hadn't been touched by human hands. Humans hadn't altered it And this viewpoint can have some very dangerous implications. I chatted to Rowan about this and he gave an example.

Rowan: The whole environmental movement's really interesting and know, in the US when the national parks were made, the great national at first sight you think, well, they're all wonderful things. But the philosophy behind them was to get rid of people, get rid of Native Americans that were living in the lands around Yellowstone and Yosemite. because the people who set up those national parks thought of wilderness, of this idea of something without humans in it, where nature could thrive without humans. But humans did live there. And it was wrong to get rid of them. So again, we are all part of this and we've got to acknowledge that and work all together with it. And that's why it's called togetherness.

Jenny: Yeah, this is a super, super important point. And it's only actually really recently that certain societies have started kind of viewing humans as separate from nature. And it's that view that has led to complete abuses of human rights in the name of environmental protection. It's a really, really important topic. And I know that both of us are really keen to return to this in a future episode. So my next question. We've been looking at this from the perspective of does it matter to us that we're part Neanderthal? But I kind of want to flip it a little bit. So did it matter to Neanderthals that we bred with them? Did homo sapiens actually cause Neanderthals to go extinct?

Rebecca Nesbit: I like your flip and you'll probably be pleased to know we didn't. Probably lots of factors contributed to Neanderthal extinction. Their population was always small, making them vulnerable to extinction, particularly because they lived in smaller groups than humans did. Humans lived in groups of up to 150, whereas Neanderthals were living in groups of about 15. So those smaller groups themselves were very much at risk of extinction. Also, the climate was changing rapidly and that had implications for the food supply. Humans were adaptable here because we were omnivores, we could change to more different food sources, whereas Neanderthals were more carnivorous, so they weren't able to adapt when animal populations changed. So not only did we not make them extinct, but we saved their genome. There has never been more Neanderthal DNA on earth than there is now. We might only have very small amounts in us, but there's so many of us compared to the size of the Neanderthal population that there's never been so much. Neanderthal DNA is thriving.

Jenny: That's a really cool perspective actually, that's an interesting way of looking at it. Because essentially through interbreeding species it's likely that we've actually saved this particular Neanderthal DNA. And what's funny about that is that is something that is very, very rarely valued in conservation. If a species were looking likely to go extinct, we could potentially save their DNA by interbreeding them with a similar species. but we actually actively resist this. We kind of fight against this. So for example, we don't try and breed domestic cats with wild cats in order to keep the wild cat gene pool alive, even if wild cats went extinct.

Rebecca Nesbit: This brings us back to exactly where we started with this conversation about humans interbreeding with Neanderthals, because in episode three, we were talking about it when we were discussing whether biodiversity has intrinsic value. So that's value in its own right simply because it exists. And biodiversity includes diversity at the genetic level. So if biodiversity has intrinsic value, then genetic sequences would have intrinsic value. so that would make it a legitimate conservation strategy to save wildcat DNA by breeding them with domestic cats. We'd have saved the genes, saved the genetic sequences, but I don't think that is gonna catch on as a conservation scheme. And that is another nail in the coffin for biodiversity having intrinsic value. Obviously I could discuss this forever, but I'm not going to. So if you're interested. head to episode three. And if you want to be part of this discussion, please leave us your comments on CashAmongThePenguins.com. We'd love to hear your perspectives.

Jenny: very sensible not to get us spiralling into another intrinsic value debate.

Rebecca Nesbit: yes.

Jenny: Good sidestep. So we have covered a lot of ground this episode. It's a really complex topic and there are a million more threads that we could pull out. But for now, I'm gonna conclude that I think it does matter that we're part Neanderthal. I think it matters both on a practical level. it... does seem that it's shaped human evolution and it still actually plays a role in shaping our health today. But it also kind of matters on a philosophical level. So it reminds us that we are actually a part of nature. We're not completely separate and completely removed in the way that we sort of tend to see ourselves as. We're actually really connected and a part of this ecosystem.

Rebecca Nesbit: think if we start to understand that, then it could have benefits for us as individuals, for our sense of belonging and for our mental health. And it could also benefit us on a societal level, if it helps us value and protect the ecosystems that are sustaining us. And conservation has a lot to learn if we understand that it's not automatically bad for humans to change the rest of nature. So we can then embrace the fact that change can be positive and in the current conditions necessary.

Jenny: for sure. Change is not only inevitable, it is, as they say, the only constant in nature. So we just have to work out how we can harness and potentially steer that change in a positive way, which ensures that we are protecting the ecosystems that we rely on.

Rebecca Nesbit: that we really need to protect the ecosystems we're part of, otherwise we risk going the way of Neanderthal extinct. It's quite a thought to end on, but it's all we've got time for today. Thank you very much for listening and see you next time on Cat Among the Penguins.

Jenny: See you next time.

Rebecca Nesbit: Thank you very much for listening to Catamom and the Penguins. We'd love to hear your take on the issues we've discussed today. Head over to our website, catamomandthepenguins.com, to see the show notes and leave us your comments. We'll be discussing these comments in the final episode of our series. To make sure you don't miss it, please click like and subscribe on your podcast platform or follow us on Instagram. Your support is greatly appreciated. Thank you. See you next week.