Instant Genius - The origin and evolution of mammals, with Dr Elsa Panciroli

Episode Date: January 10, 2022

Palaeontologist Dr Elsa Panciroli takes us 300 million years back in time to an age long before the rise of the dinosaurs to chart the evolution of some of our most ancient ancestors.Once you’ve mastered the basics with Instant Genius, dive deeper with Instant Genius Extra, where you’ll find longer, richer discussions about the most exciting ideas in the world of science and technology. Only available on Apple Podcasts.Produced by the team behind BBC Science Focus Magazine. Visit our website: sciencefocus.com Hosted on Acast. See acast.com/privacy for more information. Learn more about your ad choices. Visit podcastchoices.com/adchoices

You said this place was steps from the water. We just haven't found the steps yet. How much did we save? Enough. Enough to get lost. Or you could book a stay with Hilton. Welcome to your oceanfront room. Just steps from the water.

The Hilton sale is on now. Book on Hilton.com or the Hilton app and save up to 20% to get the stay you expected. When you want savings, not surprises. It matters where you stay. Hilton, for the stay. Ambition comes in all shapes and sizes. At First Citizens Bank, we roll with your goals because we're built for what you're building.

Fit for your ambition for Citizens Bank. Peak pollination season, and my business is scaling fast. To keep the nectar flowing, I need a phone plan with top priority data speed. That's why I chose GoogleFi Wireless. My connections stay strong even when the hive is buzzing. Plus, unlimited plans started $35 a month. Now that's a deal that doesn't stay. Explore GoogleFi Wireless plans today.

Plus taxes and government fees. GoogleFi Wireless is not subject to data traffic deprioritization during times of high network usage. This podcast is sponsored by name, audio and focal. Streaming has made music more accessible than ever, but true listening is about more than ease. It's about quality. British audio experts name audio, alongside French acoustic specialist focal, combine handcrafted tradition with cutting edge. innovation and high-end materials, delivering digital precision with analogue warmth. So you can experience

exceptional sound at home. Music just as the artist intended. Visit name audio.com to learn more. And welcome to Instant Genius, a bite-sized masterclass in podcast form. I'm Jason Goody, commissioning editor at BBC Science Focus magazine. In this episode, I talked to Dr. Elsa Panchiroli, a paleontologist and writer, about her book, Beasts before us, the untold story of of mammal origins and evolution. I just finished reading your book. And the first thing I learned from reading it and perhaps the main takeaway that I have from it now

is that something I didn't know before, mammals go way back. So there's a line that you say in the book that mammals ruled the earth when the dinosaurs weren't even a twinkle in the planet's eye, which I really liked. So I thought, let's start this at the beginning and go way back to when there was only one supercontinent,

Pangaea on the Earth. and the very beginning of this thing. So how long ago are we talking about, if we talk about this, and what was the earth like back then? I think this is one of the things about sciences, where you decide to draw a line and draw a boundary. And so, you know, conventionally, when we're thinking of mammals, we do think of them as a much more recent thing

because we're drawing a very recent line under them. But if we trace our ancestry right the way back, we don't share an ancestor, for example, with reptiles. We actually are an independent lineage right the way back. Around about 300 to 320 million years ago is where we can trace our earliest, earliest ancestors too. They do share an ancestor with reptiles, but that ancestor isn't a reptile or a mammal.

It's the thing that came before. It's what we just call a tetrapod, which of course just means that it has four limbs and four feet. And the world would have been quite a different place, we have this single supercontinent, or it's just forming at that point. And as a result, you get very, very different climates and weather systems. So we're looking at, you know, these sort of monsoonal sort of climates coming in off this, off the sea, because the sea, of course, is also one massive sea. So I describe it as a kind of genus world. You've got sea on one half and land on the other.

But you're also looking at a time before lots of the different plants that we know today exist. There are no, for example, flowering plants at all, no flowers, nothing like that. The dominant forests, I'm using air quotes, you can't see me, but I'm using air quotes. Because of course forests today are made up of flowering plants, but they're also made up of conifers. Neither of them were that, well, they didn't exist or they weren't the dominant plants at the time. The forests were made up of things that were more closely related to club mosses and quill warts. plants are today very, very small, but at that time were 30 metres high or more. And it was hot and very humid and swampy.

And there was the highest level of atmospheric oxygen that we've ever known on Earth. So it was quite a sort of volatile kind of a climate because obviously, you know, lots of oxygen equal, lots of fires, forest fires being triggered. So despite the fact that it's swampy, we also see evidence for these forest fires raging through every so often. So a very interesting planet quite different from the one we know today. Yeah, I mean, you set quite a scene in the book with your descriptions. One thing that stood out to me as somebody is a bit squeamish with insects is that there were giant millipedes and giant dragonflies wandering around. And I just thought that was terrifying. Oh, I know.

So that's the other consequence of having a lot of oxygen in the atmosphere. today insects, the biggest ones are about the length of a sort of adult human hand, a big hand. So around about 15 centimetres, something like that is the sort of biggest. And they're limited by how much oxygen they can get into their bodies. Because of course they don't have lungs. They have a sort of passive system of absorbing oxygen. So if you've got more oxygen, you can have much bigger insects. And we did.

I mean, there's evidence foot steps, for example, which you call them like trackways. of millipedes the size of bikes basically. They're huge, huge big things, meters long. So yeah, if you don't like insects, you do not want to go back to this time period. So you mentioned there the tetrapods. That's going to be our sort of ground zero from here. So these themselves emerged from evolved, sorry,

from sort of fish, shall we say, and they came out of the swampy water onto the land. So could you tell me a bit about that? What was going on there? Yeah, so they did. Not only did they evolve from, fish, but if you ask somebody who studies fish, quite a lot of them make the joke that we ourselves are actually just very highly derived fish. We're all fish, all backbone animals on the

planet, really all come from fish. So, yes, we see this sort of fundamental split among fish groups of what we call ray-find fishes, which is most fishes on the planet today, and then the lobe-finned fish. And that's what we are as well, although obviously, we've changed quite a bit, but we do still see lobe fin fishes around. We have things like silicants and lung fishes. And basically the difference, one of the sort of main differences, is they have bones in their sort of front fins, which rayfin fishes don't have. And it's those bones, of course, that are the precursors to a limb. So yes, at this time, right back at the beginning, we do see these first animals probably using these original limbs, probably for pushing vegetables,

pushing vegetation aside while they're still living in the water, rather than for this sort of classic idea that they grew them to walk, which of course, it doesn't... Evolution, as we know, doesn't work like that. But they possibly co-opted them and ended up using them for that purpose. So right back at the beginning, we have this ancestor. It's a tetrapod. It's come from this branch of fishes. And it is basically neither an amphibian, a reptile or a mammal. It's the... prototype of all of those things. It's the starting point. And then we see the branch that leads to, that eventually includes amphibians, branches first. And then we have the branch that we're on along with reptiles. And they're the tetrapods that lay eggs that have a covering, an outer shell. So as you said there, like these early tetrapods with their shared ancestors of all life on earth

with the backbone and four limbs. I mean, that's a pretty astonishing thing to think about, think about really, isn't it? So what would they have looked like? It's a good question. It's always difficult to describe ancient things that no longer exist because we look at them with such a biased perspective. We're always looking backwards. And of course, linear time doesn't work that way. But we look back and we think, you know, if I was going to just pluck a description out of the air, that they kind of superficially look maybe a bit lizardy, you know. They would have a sort of sprawled limbs out to the side. And at first, they were relatively small, maybe the length of your forearm,

with sort of flat, wide heads. And a lot of them have eyes sort of sitting more in the top of their heads rather than at the side, probably, so that they can look up out of the water, perhaps looking for insects, which they might have been eating off the land at the water's edge. So they all kind of looked sort of like that at that point in time. But of course, as I say, I say they look lizard-y,

but obviously I'm looking back in time, lizards kind of look early tetrapoddy. It's the other way round. So as we said, we're going about 300 million years here. That's completely incomprehensible amount of time for a human being. And you've just described to me what these looked like. So how on earth do we know that? That's a very good question. So this is the area, I don't specialize in these annals themselves, but I know a few people who do. And they spend an awful lot of time, of course, reconstructing the skeletons of these creatures and comparing them to the closest living things that we can observe today in terms of how they might have moved and held themselves. Could they actually, for example,

lift themselves up on their legs and walk? Or were they dragging themselves along? This kind of thing. And really, it all comes down to their skeletons. At this point in the fossil record, we don't really have any other evidence to go on. Later on, we do have some soft tissue preservation of some of our ancestors. But at this point, we don't really have many things like that. So it's all based on their skeleton. It's observation of how the skeletons

put together. So yeah, as we said there, these are the shared ancestors of backed-fowned, four-limbed life on Earth. And you mentioned the action of evolution that's led from that point over millions and millions of years

to the point that we're at now. And you mentioned there's no grand plan or guiding hand behind evolution. So how, how? How does that work? How does evolution get us from tetrapods through all of these various different iterations of mammals and then eventually to human beings? That's an enormous question. It would take about five. It would take more than five podcasts for me to answer that.

I mean, I guess the kind of short answer really is. Well, here's the way I see evolution. I see it as a kind of glorious serendipity. And it doesn't have, you know, it does not have a destination. There definitely is not a plan to all this, certainly not in my opinion, although obviously some people have disagreed in the past. But it tends to be in response, of course, to changes that are going on in the environment around any living creature. So changes occur in populations rather than individuals.

So, you know, for example, when it comes to the first animals to walk on land, it wasn't that one pioneering individual, you know, started walking on land and everyone else copied or whatever. It occurs in populations and it tends to be, you know, that really there's a lot of randomness and a lot of variation within any population. And obviously any trait that gives an animal or a population of animals an advantage that basically proliferates in that population. So, you know, in the case of walking on land, there's lots of different theories for how this could have happened. happened, why it might have happened. But certainly one of the possibilities is that with insects having already moved on to land, it could have been that there was a lot of food up there. And so those animals that already had limbs, so they could push their way through these swampy streams

and so on, those that were strong enough to be able to pull themselves out and eat some of those insects would have perhaps done better and would have perhaps had more offspring and therefore passed on this ability to be stronger on land and so on and so on. It multiplies through thousands and millions of generations. So really, it's a tiny, iterative changes like that that just make something survive a bit better. But when you look at the crazy things that end up happening through this process, it's understandable why people can hardly believe it's true, because it's really amazing. But it's all just a matter of time. We're talking about millions of generations and with that kind of time school you can do some pretty bonkers things to any

skeleton or any animal. So you mentioned there at one point the kind of the family tree split between what would end up becoming mammals and us and reptiles. So, you know, what sort of when was that and what was going on? What were the key differences in that split that we can discern between the two branches? So there's quite a lot, there's what we would call a sweet, of differences of characteristics in skeletons of fossils from that time. It's about the same sort of time around 300 million years ago

that we were just talking about. A suite of characters that we can point to and say, this tells us that this belongs to one group or another. But really, when it comes to the difference between the sort of reptile line and the mammal line, one of those differences is the one that most people

focus on. And that's in the skull. And if you feel your own skull, just behind where your eyes are, behind your eye socket, you can feel this little indent in the side of your skull. And that is this single sort of hole that we have in the side of our skull. And that is the characteristic of our lineage, that we have one of these holes. Our one doesn't go right through the skull.

It's basically kind of, as I say, beside the eye and the side of the head. But reptiles, they have two holes on the side of their skull, although some of them have gained or lost holes and that's a very complicated, messy story on their side. But for our lineage, for the mammals, it's one hole in either side of the skull and it has been right from the beginning. And it's the kind of telltale mark

that we can use to look at the fossil record and say, yep, that thing, that's one of our ancient ancestors as opposed to it being on the reptile line. So that is really, yeah, that's really the smoking gun that we look for. there are other things, lots of different little tiny details of the skeleton as well, but that's the number one. Yeah, that's really interesting. So sort of moving forwards from that then, we come to something that you call in your book the first age of mammals.

So this is something that I think, I mean, it's quite often omitted from different textbooks and things. I think a lot of people will be unaware of this. So when was this? What was the period? What was it called? what was happening on the earth during this time? Yeah, so I was a little cheeky with that title because we consider ourselves, of course, to be living in the age of mammals now. But yeah, this is in what is called the Permian. So just over 252 million years ago.

So this is the time period after the one we were just discussing, which was the Carboniferous. And in this time period, we see this first sort of flourishing of that line of animals that we belong to, the ones with one hole in either side of their skull, they're called synapsids. We are also synapsids. And yeah, as you say there, I mean, really we don't hear much about these animals.

One of them you'll probably all be familiar with, and that's an animal called Demetrodon. And you might have seen it hanging out with dinosaurs, which it shouldn't be in any reconstruction. But it looks, well, the way it's been reconstructed in the past has always been that it looks kind of like a giant reptile, like a lizard, with a huge sail on its back, like a sort of Mohican almost, all the way down its back. And as I say, this has traditionally been lumped in with the dinosaurs, but it's not. It's actually one of our ancient ancestors, very much on the mammal line, and lived very much earlier in time in this time period I'm talking about the Permian. And these creatures, basically, you know, we think of it being, certainly the Victorians anyway,

they thought of us having an age of fishes, then an age of reptiles, and then an age of mammals. But in fact, at this time period, before the dinosaurs, it was our line, it was the mammal line, creatures like Demetodon and then the ones that came directly after it, they were the ones that really proliferated. And they grew to very large sizes. We have creatures the size of great big buffalo, you know, big plant eaters. We have specialist carnivores, some of them with the first saber teeth that we see in any animal, you know, very specialised in meat eating. But we also have some little diggers and tree climbers, basically a kind of first flourishing of our ancient ancestors, our lineage. And they're not technically mammals at this point, but they certainly are

on the mammal line. They're part of the same group as us. So it's a really incredible time period, but for some reason, we never really talk about it. It's not on the TV shows, really, you know, apart from Demetodon, which always gets misclassed. And I have no idea why that is, because it's an incredible time period. Yeah, I mean, I found it super interesting. It was something that I knew next to nothing about, but, you know, before reading the book. So just saying that this sort of flourishing of these animals, was there a kind of, how can I say, like a path through, so was it initially we had early success from herbivores and then we had the emergence of carnivores later on, or was it more of a sort of simultaneous thing. It's really a kind of, we talk about the sort of emergence, really,

of a sort of ecosystem that we might recognise. And it's sort of happening altogether. You know, all of these creatures are kind of interconnected. There's lots of different families and they're doing lots of different things. But it is the kind of first time that we start to see on land, this is, mega herbivores, as in very large bodied ones, and mega carnivores. So this is a kind of novel thing. Just looking back in evolutionary time, you just have to be able to be. You just have to be a very haven't seen this until this point. So it's quite a sort of innovative time really for, in terms of evolution in general, that we start to see this. I mean, it's really all happening through the Permian, particularly in the second half of the Permian, you start to get lots

and lots of different groups, including the line that would then lead on to us, which are a little, at this point, a sort of underdog, literally, little underdog called synodons. They emerge at this point as well. world has begun to dry out. It's very arid in the centre of this supercontinent. And really, yeah, they all start to emerge kind of at once, lots and lots of different lineages. But they don't last, of course, because as we all know, we then have the dinosaurs after that point. But what might have happened if they hadn't become extinct is something that certainly I love to sit and think about how different the world might have been. So we mentioned there, this is all occurring during the Permian period. So how long was that? When did it span from and when did it end?

So the Permian starts just when the Carboniferous ends. So around about 299 million years ago and then it finishes 252 million years ago. So it's about 50 million years long, basically. So quite a long period of time. If you think that the time period we live in now began 66 million years ago. So we're looking at a time period similar to the one in which mammals have once again come to be some of the dominant creatures on the planet. So you mentioned there something earlier that I think a lot of people will be interested in. And you said there was the emergence during this time of the mega carnivores such as the perhaps probably the most, I think, iconic extinct mammal, a saber-tooth cat. So what were these animals like? Yeah. So in the book I talk

about sabretooth because I think of all the kind of extinct mammals that people know about, we all know about saber-toothed cats and we all tend to really love them. They're really sort of iconic, aren't they? But saber-toothed cats are really very recent. Only in the last 50, 60 million years have we had those, which to somebody who works in millions of years is very recent, although obviously not on a human time scale. But in this, in the Permian, time period, we do have the first animals related to mammals on our lineage with sabre teeth. Some of the most iconic ones are these creatures called Gorgonopsians, which I think is a fantastic name coming from the Gorgans of Greek myth. And these things, I mean, I guess you've got to

kind of imagine them as, if you imagine, an enormous, hairless tiger with huge saber teeth probably would have had, its legs would have been slightly further out to the size. than a tiger. So of course, modern mammals have their limbs right directly underneath them. This creature would have been a little bit more sprawled, but it still would have been able to move extremely quickly. Certainly, I would have thought, outpacing any human who might have accidentally found themselves back in the Permian, and they would have been feeding on these massive herbivorous creatures that lived alongside them. So it's quite, yeah, they're, I guess, the sort of T-rexes of the ancient mammal world. That's really interesting. There's just something there that I'd like to pick up on that you'd say it's like a hairless animal. So what do we know about when mammals started to get fur and hair and things like this?

So this is a really good question. In the past, people have reconstructed these very ancient mammal ancestors as looking essentially like reptiles. In fact, they thought that they did evolve from reptiles, although we now know that that's not the case and it's two very separate lineages. But we do know. from some fossils that have been found actually in Russia with skin impressions on them that our lineage at this point in time had what we would describe as glandular skin, which is what we've got. So in other words, they weren't scaly. They would have had a sort of smooth or nobly sort of skin,

but not with scales, not like reptiles. And as for hair, well, this is a bit of a sort of enigmatic thing. We, of course, hair is something that does not preserve very well in the fossil record. along with other what we would call soft tissues. So the oldest possible evidence for hair does come from the permeant, though. And it's actually from a fossilised poo. It's a coprolite, as we call them.

And the researchers who found it at a site in Russia, they identified what could be one hair fibre inside this coprolite. And that would mean that whatever carnivore deposited this coprolite had eaten something that had hair. but it's a little bit disputed. It could actually be a strand of fungi or something similar, so we don't know for certain. However, the chances are that hair probably developed

as part of a sensory system, probably initially from whiskers. So if at this point in time in the Permian, we do start to see creatures that are borrowers, on our lineage as well as on the lineage of reptiles, but in our lineage, some of those little borrowers probably started to develop what we now know of as whiskers, and that would help them feel their way in the dark.

And certainly a little bit later on, just after this time period in the Triassic, we start to see other characteristics in the skull that give us clues that probably animals almost certainly had whiskers, and we think if they had whiskers, they probably had started to develop hair in general, because it's very useful. It not only keeps you warm, you know, in chilly temperatures,

but of course it allows you to sense your environment all around you at all times. So one of the main ways in which we've traced back the development of hair in our lineage has been actually through the skull, which is a bit of perhaps it sounds a bit strange, but two lines of evidence. One is that when animals have whiskers, they need to have lots of nerves and blood vessels on their, essentially their lips, in order for them to be able to twitch. those whiskers and to transmit the sensations that they're getting from the whiskers to the brain. So if you have lots of nerves and lots of blood vessels, those have to travel across the

surface of your skull and then through the skull into the brain. So we can look at fossil skulls and we see that the nerves that would transmit those signals, they appear in some of our ancestors around about 200 to 220 million years ago, and that's in the Triassic. And then similarly from studies of the development of actually of mice in the laboratory, there's certain genes that when they turn on and off, they change an animal's ability to produce milk, to look after their hair, so the kind of secretions and things in their skin that maintain their hair. Those are also interrupted. And they're connected to this hole that we have in our skulls called a parietal foramen, which is in the very top of your skull

and in humans and most mammals it's closed. We don't have a hole. We have it when we're babies. Anyone who's had a baby may know that the very top of the skull is very soft because there's a gap there. And that's all that's left of this hole in our skulls which all animals once had.

But in mammals, this closed up. And again, it looks like this happened around about 200 to 250 million years ago in the Triassic. So when we take all those bits of evidence together, that's our kind of time period that we think that the first, not only the first fur appears, but probably also the first milk starts to be produced as well at the same time.

These things are probably related to one another. Continuing to think chronologically, we say we've reached a point in the timeline now that you've said you cheekily called the first age of mammals. So mammals, they're doing great. You know, we've got mega herbivores, mega carnivores. But at some point, something goes wrong, doesn't it? Well, one of the things that I really emphasize in the book is the sort of cyclic nature of evolution,

that there are constant cycles of these amazing new flourishings of creatures, but there's mass extinctions constantly. I mean, they happen all the time from small mass extinctions right up to what happened at the end of the Permian, which was one of the, in fact, it was the biggest mass extinction on Earth of all time. and it was a pretty brutal event. It looks like it was triggered by massive volcanic eruptions in what's now Siberia. And these eruptions, they spewed out. I mean, enough lava to sort of cover an area the size of China, you know, hundreds of meters deep.

You're talking possibly miles deep. This is an absolutely devastating event. So not only would it have, of course, killed the animals within the vicinity, but as we know, you know, things like volcanic eruptions, they release a lot of greenhouse gases, particularly sulphurs and aerosols, and those would have radically altered the climate. First, of course, creating, you know, smothering the planet, creating darkness with all of the sort of ashes and things that would have been in the atmosphere, but then raising the temperature and raising it to the point where some studies indicate that at the equator, if you had dipped your foot,

in the ocean to go for a swim, it would have been as hot as your evening bubble bath. I mean, we're looking at like 40 degrees ocean temperature. That's how hot it was. So this, of course, is devastating and devastating for everything. This is one of the only mass extinctions where we actually see extinctions among insect orders, which doesn't usually happen because insects are quite resilient to mass extinction events. So, yeah, it basically puts an end to this. first flourishing of our lineage of these creatures called synapsids and therapsids. And it resets

the evolutionary scene. You know, it sort of starts the clock again. And this time, rather than it being our ancestors that are the first off the mark, it's the reptiles who get there first and begin to grow large and take a lot of the niche space up in the ecosystem. And so we have the the so-called age of dinosaurs. Thank you for listening to this episode of Instant Genius. That was paleontologist and writer, Dr. Elsa Pancheroli. If you want to know more about the fascinating history of mammals, check out her book, Beasts Before Us,

the untold story of mammal origins and evolution. Or to hear her tell me more about the evolution of mammals, head over to the Instant Genius Extra podcast. The Christmas issue of BBC Science Focus magazine is out now. Pick up a copy in store, or visit sciencefocus.com. This podcast is sponsored by Name, Audio and Focal. The texture and emotional depth of music

can be lost through digital sources or poor signal. Name Audio believes you can have digital precision with analog warmth. Alongside French acoustic specialist focal, name creates high-end audio systems combining innovation with craftsmanship so you can listen to music, just as the artist intended.

Discover more at name audio.com. You can't reason with the sun. Trust us. We've tried. This summer, it's time to put that angry ball of fire on mute. Columbia's Omnyshade technology is engineered to protect you from the sun's harsh rays that can burn and damage your skin. The sun is relentless, but so is our gear. Level up your summer at Columbia.com to spend more time outside

and less time slathering on all loation. You're welcome. Columbia. Engineered for whatever. There's a moment when you start to wonder, what's the right next step? Not about changing who they are, just finding the right kind of support.

At Kingsley Manor, life stays expressive, connected, and full of character, shaped by people who have lived interesting lives and aren't finished yet. So it doesn't feel like a change. It feels like a continuation. Explore your options at canesley manor.org,

a non-profit month-to-month senior community within the Front Porch family.