371 | Kyle Harper on How Humans Have Shaped Life on Earth

History, Science, and Human Impact

0:00Hello, everyone. Welcome to the Mindscape Podcast. I'm your host, Sean Carroll. You may have heard that species of lifeforms here on Earth are dying out at an unusually high rate. Sometimes this is called the sixth extinction, or the Holocene extinction, or the Anthropocene extinction, just compared to the rate at which species go extinct, which of course always happens, right? There's never any moment where no species go extinct for an extended period, because life is dynamic and things happen. But the rate can change over time. There have been a series of catastrophic extinctions in past history millions of years ago. But right now, species are dying out at a greater than usual rate, noticeably. And we know why. It's because of us, because of human beings changing the planets in different ways.

0:52But the precise extent to which what's going on right now is best described as a new massive extinction event is slightly controversial. And long-time Mindscape listeners will not be surprised to learn the situation is somewhat complicated in various ways. So it's not that species are not going extinct. That's absolutely true. But is that the right way to think about what is happening? In general, human beings are causing all sorts of changes to the Earth, to the biosphere, to the ecosystem.

1:27And species going extinct is part of that. But is it the most important part? Is it the special part? What else is going on? And what can we possibly do about it if we think that there is a cause to stop what is going on right now? So today's guest, Kyle Harper, is actually a historian. But he's a historian who has long felt that science, natural history, the understanding the physics and biology of the Earth on which human beings live, should be an important part of history.

2:04And the way that the environment shapes human history has been well studied. And what climate change is right now doing to the environment has been well studied. But the whole sort of history of how human beings have affected their environments and the world in which we live is a little bit less studied. So Kyle's new book is called The Last Animal, Human History and the Fate of Life on Earth from the Ice Age to the Sixth Extinction. And he takes a historian's view and he starts from when human beings were first starting agriculture and domestication of other species and so forth, how that changed the different kinds of species that are around.

2:48And it's not just the number of species that are dying, but it's which ones and how that affects not just the numerical quantity of species, but the complex web with which they interact with each other. And he takes it right up to the present day where, indeed, climate change and other things are having an important impact. So we tried at the end of the podcast to end on an optimistic note, because that's what we like to do here at Mindscape. But, you know, to be optimistic means to first be realistic, to look at the world and what's happening, get your facts straight, understand what is going on.

3:26And that's what this particular episode is all about. What we as a species choose to do about it, that's going to be up to us. So let's go.

3:36Kyle Harper, welcome to the Mindscape podcast.

From Roman History to Ancient DNA

3:53Hi, Sean. I'm a big fan of the show. Thanks for having me. Oh, very good. We love those kinds of guests. I know that we're talking about there's very big issues that came up in your new book about humanity and extinctions and the bio. And the biosphere and things like that. But I'm a little bit curious about the trajectory. You know, you started writing books about ancient Rome. And that's what historians are supposed to do. We understand that. That's history, ancient Rome. And then somehow now you're talking about biodiversity and things like that.

4:27Tell us a little bit about how you get from A to B. Right. Well, I'm a historian who would love to see a world where that doesn't seem quite as weird or unusual as it might. And to tell it in personal terms, I, as a student, as an undergraduate, loved both the humanities and the sciences. And when you go to graduate school, you have to you have to pick for for good reasons, but also with some some negative consequences. But I was very fortunate to go to a Ph.D. program in history where I was really encouraged to to cultivate my my interest in the natural sciences.

5:06And it also turned out to be good timing because people who work in history right now benefit from all kinds of different ways that what you might, you know, would consider natural science fields are helping us understand the human past. And that includes things like paleoclimatology. Obviously, there's a very urgent need to understand how the climate system works. But that inevitably means you have to understand how it's worked in the past and under different conditions. And so there's been a lot of great research and a lot of funding for research in paleoclimatology, reconstructing the past dynamics and states of the Earth system.

5:40And so for those of us who are, say, in Roman history, you know, this wasn't funded with the goal or intention to benefit us. But it does benefit us if all of a sudden we now have high resolution paleoclimate proxy records that tell us what the climate was doing in the human past. We can then start to ask new questions and we have new data. So as a historian, I've really not only just have a kind of natural inclination for the sciences, but have benefited from the fact that there's all kinds of cool new data.

6:12And DNA is probably the big one, just the advances, leaps and bounds in the ability to sequence DNA, both DNA taken from recent samples, living people, but also from ancient DNA, archaeological DNA taken from dead people that tell us about the evolution of humanity, but also the evolution of animals, the evolution of microbes. And so as a historian, that was sort of my pathway into environmental history, a kind of history that tries to understand our place in the natural world, that, you know, it's partly humanistic, but it's partly scientific.

6:52I think you have mistakenly piqued my interest here. How much ancient DNA do we have? Like how many ancient Romans have we sequenced their DNA? Yeah, so I can tell you 10 years ago, that number was zero.

7:07And today, the number of published complete human genomes sequenced from the Roman period would be on the order of a couple of thousand. So it's still new, still new. There've been, you know, maybe five papers on populations from Italy. Then I was part of a team that published 150-something genomes from the Roman Danube, Serbia. We've got a paper that's about to come out on Roman Spain. So, you know, the number is quickly, quickly growing.

7:40And that means, you know, more samples doesn't just sort of like expand the picture. It lets you ask deeper and deeper questions. You have higher power. You can ask all sorts of crazy questions that, you know, the challenge now is almost inventing the questions fast enough to keep up with the amazing data. Is there anything in particular that we've learned that has surprised you a little bit? Oh, there have been tons of, I mean, really like true surprises where, in some cases, ancient DNA can answer questions that you just didn't have the ability to answer before.

8:11I mean, one of the big ones is sort of like what pathogen caused the Black Death, where we thought we knew, but there were lots of questions. What pathogen caused the Plague of Justinian? So sometimes it answers questions that you know you should be asking. And then sometimes it, like, causes you to answer questions you didn't know you should be asking. So like the paper I mentioned from Roman Serbia, which is a really important region for the Roman Empire. All the late Roman emperors come from here, like Constantine, Diocletian. This is a really important province that we think of as deeply, deeply Romanized.

8:43It becomes a Latin-speaking province. And we have, in the historical, like, written sources, all kinds of evidence that the Roman legions come and they, you know, are colonizing, building cities. And so we assume that there's, like, a huge number of people from Italy flowing in and taking over this region. And, of course, like, you know, the picture will continue to evolve as we get more and more genomes. But, like, 150 is a pretty good starting sample from highly Romanized context of this Danubian provincial capital.

9:14There's nobody from Italy. Like, we can't find traces of the genomes, you know, even in subsequent generations. You'd expect, like, because a lot of these people are from second, third, fourth century. So surely they had kids and grandkids and great-grandkids. And so at least in this region, it starts to make you ask, wait, what did colonization mean if it didn't actually mean the movement of people into colonies? This is a kind of Romanization without Romans. That's just one example. There are so many people from the East Mediterranean in the Roman Empire everywhere, in Italy, in Serbia, in Spain.

9:51And, like, we don't understand this now. The slave system is probably capturing people. We know the Romans have lots of slaves. But, like, we don't actually really have a good understanding right now of how so many people from Anatolia and Syria end up everywhere in the Roman Empire. And so that's kind of a hot question that really we weren't asking before. So, yeah, there's lots of cool new knowledge that we're grappling with. Well, it gets into another question I wanted to ask, because, like, already in your early work on Rome, you were also talking about the natural world, you know, with plagues and things like that, right?

10:31But then there's this whole separate thread of ideas and how they affect history. And you talk about the early effect of Christianity and how, like, it really did change people in some ways. And are you saying that in the Serbian Romans the colonization was more in the mind than in the body? Well, yeah. And, of course, like I say, we'll find out with more genomes, too. But I think that absolutely has to be a big part of the answer. And really, like, I'll go back to the point I made that it's hard to explain.

11:04And, like, all of the people who ruled the Roman Empire for the last three centuries all come from a tiny area about the size of Scotland that's right there on the Danube in Serbia today. They all come from there, all of these Roman emperors. And they claim to restore the Roman Empire. And they're sort of, like, more Roman than the Romans. And now we have to think of this story as one where, like, it's a cultural, ideological change. But it's deep enough that they change their language.

11:35You know, they worship the Roman gods. It's a deep, deep transformation. And I guess there's probably some temptation if you're a professional historian to—I'm going to be unfair here so you can put the nuance in where it belongs. But people have, like, a lens, a point of view, right? I mean, some people are going to think that the ideas are the most important thing. Other people are going to think that government and military is the most important thing. Some people might think that geography and ecology are the most important thing. But they're all there, and you have to balance them somehow.

12:07Well, the good news is that's going to keep historians employed for the foreseeable future. Human societies are complex. And, you know, we all have our pet theories. And it usually goes back to whatever you wrote your dissertation on. Yep. But that's the good thing about human societies is they are the most complex thing we know of and so many important dimensions from geography to the gods that they worship that are actually important for questions that you might really want to ask.

12:39And so what is it that particularly made you think, you know, I have to understand how humans are affecting the biosphere? Yeah, I mean, it was, I think, in part, like, it's just pure presentism, like people sometimes get anxious about this. And obviously, we don't want to judge the past by our standards. We don't want to distort the past to, you know, make it fit into our view of the world. But historians are, you know, normal people.

13:09And we're interested in the problems and challenges we face in our lives collectively and individually. And you bring that with you when you go and you read a text. And so, you know, it's no accident that it was historians in the 70s who started taking gender seriously. They lived in a world of the, you know, second wave feminism, sexual revolution. And so they went and they read the same text. And all of a sudden, they were seeing different things. And so partly, we live in a world where some of the most profound challenges we face are our relationship with the natural world, environment, climate change, biodiversity.

13:43And so when you read an ancient text, you're sort of sensitized to see things that maybe weren't as, you know, leaping off the page in the same way for previous generations. Partly, it's that, as I said before, we're learning new things. And as a historian, you know, you always kind of want to make the biggest contribution that you can. And sometimes that comes from writing the thousandth dissertation on Tacitus or whatever.

14:13But then when you know we're getting DNA sequence that tells you truly surprising new information, that's just sort of irresistible. It's kind of magnetic. You're drawn to it.

Shifting Baselines and the Pleistocene

14:27And, okay, so the effect, I mean, there's been a bunch written about how the environment or geography or whatever affects human history. And in some sense, we're now sort of flipping it on its head and saying how have we affected the environment and the world around us. Everyone knows we're doing that now. But part of your new book is we've been doing that for a very long time. Right. And we've been doing it for a very, very long time. And, you know, it was marine ecologists who came up with the term shifting baseline syndrome, which is the kind of natural, both human and scientific tendency.

15:08You want to measure something. So you need something that you can measure. And we live and therefore tend to think on human timescales. And so when we measure something like how humans have changed ecosystems, there are a lot of inbuilt sort of prejudices towards trying to establish a baseline that we can lay down, make firm, measure since that time. But if you want to ask, you know, where does human impact on the biosphere start or even, you know, this isn't my this is I don't want to get us off too much on this, but like it's actually a really interesting question and an open question.

15:50When do humans start to influence the climate system? Yeah, because there are serious arguments in the field that in some ways the origins of agriculture, deforestation, rice farming contribute to human alteration of the global planetary climate dynamics very, very early, thousands of years ago, eight, 10,000 years ago. So that's that's that's sort of still contested in the field. But I think the human impact on biodiversity is is actually less ambiguous.

16:22I mean, we have been influencing the the nature and diversity of the world around us for really for hundreds of thousands of years, but particularly for tens of thousands of years in really, really dramatic ways. And so, you know, the shifting baseline is a is a really hard problem because you want to be able to grab onto something and start counting things. But we always have to be sort of critical and aware that that's a that's liable to be a kind of arbitrary decision or to leave out things that might be interesting.

16:54And so the story of how we've impacted biodiversity goes back easily to the Pleistocene. Well, let me ask one of those questions that sounds super simple to ask, but is endlessly complicated to answer. When did humanity begin? Forget about humanity's effect on the environment. But, you know, when did when do you say, OK, it's humans doing this work now? Yeah, I mean, it's a it's a great question. And my colleagues in anthropology will probably fact check me. But there's a there's a an analogy that that Richard Wrangham uses in his book Catching Fire is the Harvard primatologist anthropologist that I use with my students when I'm teaching kind of a big history course or sort of like moving through the first few million years of human history.

17:39That in some sense, australopithecines are apes that we would sort of think of as not human, but members of the genus homo are human in a way that's somehow like very profound and sort of difficult to put your finger on. But the analogy he uses is australopithecines you would probably put in a zoo and say they're amazing the way that chimps are and members of the genus homo. You would probably invite to dinner and try and have a conversation and you would give legal rights without without too much question.

18:13And so, you know, that means that we're looking at, you know, two point six million years or something. Or if you want to say, you know, that really somewhere along along the evolutionary path of our lineage, homo erectus, maybe is making tools, controls fire, has symbolic language. And really, you would feel like this is a human. And so sometimes anthropologists will talk about archaic humans to refer to these species that are us, but not fully us, not homo sapiens, but are like human.

18:44You would use the word human and you would say that that's a very defensible thing. They have symbolic language. They're probably fairly altruistic, cooperative, creative beings. And the more we learn about our sort of sister species and later so-called archaic humans like Neanderthals, the more like us they seem. So the human history is probably more than two million years old. And, you know, homo sapiens, our species, looks to be more like 300,000 years old.

19:17So, yeah, when we say human, it's less easy and less transparent than we might automatically expect.

Foragers, Megafauna, and Social Predators

19:25But my impression is that, and my impression is completely ill-educated here, so tell me the truth, there weren't that many humans, like, you know, by comparison to some other animal species for a long time. Is that accurate? Yeah, I mean, yes, in fundamental terms, that's accurate. And, of course, it's hard because, you know, as somebody who's spent a little bit of time worrying about, you know, how many humans were there in the Roman Empire, which is like yesterday, we still, like, debate about that really fundamentally.

20:01And people disagree about it when you go back before there are, you know, census records and things. It gets harder and harder. But geneticists have methods to try and estimate the size of a population that's reproducing. That gives us some insights. And, of course, archaeologically, you can sort of trace how many human settlements there are and what that says about the likely population. But, I mean, we estimate that, you know, people debate about how many humans there are at the Pleistocene-Holocene transition a little over 11,000 years ago.

20:33But it's probably on the order of 5 to 10 million Homo sapiens. By that time, there's only us. We've – or the Neanderthals have gone away. Whether or not, we're to blame. But we're the only humans still in the game. And there's probably only 5 to 10 million of us. So, you know, that's barely more than the population of my beloved Oklahoma across the whole globe. So, we know that all humans until 10,000 years ago are fundamentally foragers.

21:03They hunt and gather. So, they're dependent on wild sources of food. And that keeps their numbers low. And so, there aren't ever a huge number of humans until the last 5 to 10,000 years. And your book opens more or less with the interactions between some of those humans circa 10,000 years ago and the megafauna that were – I don't know if common is the right word, but certainly there were plenty of them bouncing around here on Earth.

21:35Right. I mean, I do open this – well, actually, I go back to the origins of life and try and put sort of our evolution in the very deep perspective of the long history of biodiversity. And then move forward to the Pleistocene. I mean, we emerge in this highly variable ice age of a climate epoch. And we spread out of Africa fairly early, at least by, you know, 100,000 years, people are immigrating and exploring.

22:08And then over the last phases of the Pleistocene, we spread and we multiply. We colonize new environments. We're all still hunter-gatherers and our populations grow. So when humans move out into the world, they are moving into a world where terrestrial biomes – so we're, you know, on land – the ecosystems are dominated by big animals. And that's not just sort of like an aesthetic point.

22:38You know, it's not like, you know, cool, it's a safari. Like, these are systems, so they're food webs where there's energy flowing through them. And critical to their structure and function is the fact that animals, mostly mammals, have attained enormous sizes. And it's very easy for us to kind of forget that. I mean, we probably have seen, you know, mammoths and mastodons at the museum. But it was really – in a way, it was their world. But they – it's not like one or two species here and there.

23:13The whole landed environment where there's life is dominated by large mammals, both herbivores and the predators who chase them. And so our ancestors move out into this very, very different – it's very unfamiliar to us. Because even in the parts of the world, like parts of Africa, where you do still have significant number of surviving big animals, megafauna, you only get like a little glimpse, really, of what a world – what a different world it is. And it's easy for us to forget that.

23:43But the Pleistocene is dominated by ecosystems where big animals rule. And one of – you sort of touched on it there, but one of the big things I got from your book, like the important take-home lessons, is when there is an extinction, when a species goes away, I don't want to say – I don't want to be unfair, but not all species are created equal. You know, you shouldn't sort of think about the impact that we have by counting species. Like these megafauna really were key, even though there actually weren't that many species that have gone away.

24:19Yeah. And I think it's important to like try and get – come to grips with that from a few different perspectives. Because in one sense, I think the point you're making is – it kind of makes us reflect about how we measure human impact. Extinction is one of the really important ways we can measure human impact. And I think it's sort of been amplified by the attention that's given to the question of the sixth extinction, which is a really interesting idea. Maybe we can talk a little bit about it.

24:51But it sort of captures the imagination scientifically, popularly. And it focuses on human impact measured in terms of extinctions. But it's absolutely the case that not all extinctions have the same kind of effect on an ecosystem. That's not like a value judgment. It's just kind of an observation about the role that certain organisms play in ecosystems. And we do tend to underestimate the sheer like systematic nature of the extinction of megafauna.

25:27Again, it's not just one or two species. It's dozens of species in every continent that have dominated for millions of years that disappear in an evolutionary instant. And these are – so it's not a huge number of species relative to the total number of mammals or even total number of animals that exist. In fact, it's a rounding error in terms of the number of animal species on the planet.

25:59But it's of huge significance because of the roles that these organisms play in their ecosystems. And we – even then, it's hard for us to kind of measure because of the depth and breadth of our impact. But, you know, we can say – think about the role that bison play in prairies. They're not just sort of like a species on the landscape. They are the integral cog in the ecosystem.

26:29They provide habitat and shelter and food. They move nutrients around. This is one of the most important and underrated sort of roles that big animals play. They move nutrients that limit life around. And so that's true of whales that are, you know, eating lots of food and then pooping it out. It's true of elephants that are massively important in things like moving around seeds. Bison eat nutrient-rich grasses in sort of river valleys and so on.

27:05And then move those nutrients around the dry and nutrient-starved prairie. So when you take out big animals, it sort of affects everything else. And we systematically took out the biggest animals virtually everywhere on the planet. Tell me more about the specifics of that mechanism. Is it simply a matter that we hunted them to death or are there more complicated stories? Yeah, it's complicated. And there's a huge – I mean, there's a debate that's been going on for hundreds of years.

27:35I mean, in my book, I quote sort of the father of geology, Charles Lyle, who comes to America – actually, he visits America a couple of times. And on his second tour, he visits this place in Georgia where they'd been digging a canal. And they'd turned up this huge fossil bed of late Pleistocene animals, you know, giant bison and mammoths. And even then, like he's visiting in the 1830s, and he's talking about how, you know, remarkable it is that so many enormous animals lived so recently.

28:15And he really, as a geologist, grasped how recent this was. And he says, we really wonder but can't say, was this climate change or human hunting? And we've been – people have been arguing about it. Wow, yeah. For almost 200 years. And it's still – sometimes it's a quite bitter and sharp debate. And, you know, not to be sort of boring about it, but it is obviously it's some of both.

28:45I mean, every organism faces environmental challenges when the environment changes, vegetation bands shift, the food source shifts. So climate change is inevitably part of the story. But the thing that is new in the late Pleistocene is the spread of bands of humans who rely on hunting for food and who are very, very weird predators. Humans are very strange predators from a natural perspective because, one, we're social predators, which we're not the only ones.

29:21Wolves are the most obvious parallel, and that's kind of an interesting parallel. I'll come back to it. But, you know, wolves are social predators. And what this lets them do is it lets them kill big animals. Usually, solitary predators kill juveniles or species that are smaller than they are. And, you know, wolves are a good example because a pack of wolves can take on a moose. And that's always a pretty fair fight. The moose usually win.

29:51And but wolves are kind of weird already because they cooperate. And so it's sort of the the size of the group that is predating on big prey. Humans do that. And we do it unbelievably well. We're just the most effective social predators that that's ever existed. And then because we're toolmakers, we overcome some of our natural deficiencies and build weapons that are very good at killing at a distance. Projectile weapons, spears, especially with spear throws, autolatels, and then eventually bow and arrow.

30:25And so we're extremely capable, cooperative predators who have tools to kill big animals. And a lot of these animals that go extinct are not used to being hunted. And they're certainly not used to being hunted as adults. And, you know, nothing nothing hunts an adult mammoth. And and then we do. And they're not used to it. Big animals tend to reproduce very slowly. They tend to have smaller populations. And so they're kind of vulnerable to this the shock that is is represented by the introduction of human hunting.

31:02So we're social tool making predators. And then, you know, we also control fire. I suspect this is kind of underrated because it's archaeologically very hard to get at. But humans use fire in hunting. We know that we do this today. We do this in more recent centuries, using fire to drive big animals into traps or into bogs or into ravines or over cliffs. And it lets us cooperate to hunt really big animals and to kill in mass, to kill large numbers of individuals simultaneously.

31:37And then if all that wasn't enough, we do something really weird, maybe 20,000 years ago ish, we form a symbiotic partnership with the second most successful hunter on the planet, the gray wolf. And we domesticate dogs. And this is, you know, like the New York Yankees and Boston Red Sox. I should say Los Angeles Dodgers. Now I'm a Red Sox fan. But it would be like if the Yankees and Dodgers were like, let's team up and just form one super team.

32:13And it's very hard to say because, again, the archaeology doesn't provide direct evidence exactly how important dogs were. But I think it's an amazing, just from an evolutionary perspective, it's a strange, extremely odd, very unlikely partnership. I mean, what a weird thing to partner with your biggest rival, who is a natural born killer. Wolves are not the most obvious friends, but they become our best friends, literally, you know, man's best friend.

32:46And that seems to sort of be a part, at least, of the sort of hunting prowess of early humans. It's Kevin Durant to the Warriors, right? Oh, you had to do that. Come on, that hurts. We will never forget or forget. You're dancing around that. I know, the Oklahoma City fans. That's okay. You turned out okay in the long run. Yeah, I worked out. But I love that point because I think that when people think about humanity's effect on the biosphere, et cetera, they think of machines in the Industrial Revolution, burning coal and what have you.

33:18But just our ability to socially cooperate gave us this leverage far beyond our muscular ability early on.

Fire, Domestication, and Commensals

33:29Yeah, it did.

Fire, Domestication, and Commensals

33:30And fire is already, you know, an almost unbelievably powerful tool because we can alter entire landscapes with fire. I love talking about fire as a historian because it's so weird. People take it for granted. As far, you know, Earth is the only planet in our solar system that we know of that has fire. Fire is really weird. You have to have a combustible gas and material that you can use as fuel. And that, you know, seems to require something like life or something like plants even that put oxygen in the air.

34:03And we're the only species that's ever controlled fire. We're, you know, it's been called a species monopoly for humans. And it already gives us leverage over nature. And then the watershed after that really is domestication. So it's not just wolves becoming dogs. But then we enter into this strange multi-species alliance with ibexes that become goats, mouflon become sheep, aurochs become cattle, boar become pigs.

34:33It's a very strange, from an evolutionary perspective, it's a very weird symbiosis that gives us, that amplifies our leverage further and further and lets us transform landscapes. And it's the reason why human impact grows over time, but for a very long time. And so, yes, the Industrial Revolution is a breakthrough. But we'll miss an important part of our impact if we don't have that deeper perspective. And that perspective matters for the world around us.

35:05The megafaunal extinction at the end of the Ice Age in evolutionary time is still contemporaneous. And that's literally just inseparable in evolutionary time. And the world is still responding to that in some ways. And then we intervene in that world, but we intervene ever faster and faster. Do we know when human beings started using fire?

35:37No, anthropologists debate it. And the challenge, again, is archaeological because it's hard to say if an ash pile, first of all, they're hard to find. And then it's hard to say whether this represents controlled fire or is this like just lightning that started a fire. And so it's debated by anthropologists who study Homo erectus. I mean, I think the consensus is going to be sometime around a million to 500,000 years ago, maybe closer to a million.

36:09It gets into questions, too, about human evolution because the ability to cook obviously depends on fire. And then the ability to cook seems to change our physiology. We have, you know, it changes our physiology. We have very weak digestive systems. Our mouths are pretty pathetic. I mean, for a predator, for a carnivore, you know, we have pathetic dental equipment. And so there's debate about what's the role of fire.

36:40What does that tell us? Because we can actually follow easier in the fossil record human evolution changes to the, you know, cranium and the shape of the body. And that lets us infer sort of that maybe fire was around, but it's indirect evidence. So it's a very good question. It's an open question. It's debated. You know, it's probably something like a million years or so, give or take a few hundred thousand. Okay, good. So let's go back to the domestication, because I don't think that we're done there.

37:11I learned a new word from your book. Commensal? Commensal? Commensal, yes. Commensal. When you haven't quite domesticated, you're just like sharing a food ecosystem with the local species. And that might lead to bigger things down the road. Yeah, I think it's one of the, well, first of all, a commensal species is a term that is used in ecology to mean a species that, the etymology is sharing a table. That's what commensal means in Latin.

37:41And it means ecologically a species that isn't quite a symbiont and isn't quite a parasite. It's somewhere in between. And it's taking advantage of the ecological effects of another organism. It's sort of writing the tales of another organism. And it's a pretty loose term, because it's an ecological term that's kind of got to capture a number of different relationships. But it's extremely useful, because, you know, it's easy to say, well, it's pretty complicated.

38:12But it's possible to say, we domesticated these animals, and they're sort of in this symbiotic, weird, but symbiotic relationship with us. You know, cattle, we feed them, we protect them, and then we eat them. And that's our domesticate. But we would really underestimate our impact if we don't recognize that a lot of animals are not domesticates, but their evolutionary and ecological history is inseparable from our success. They ride our coattails.

38:43And this is true of a really shocking range of organisms. And one that I love thinking about is the housefly. In some ways, its story sort of captures the human story, Musca domestica, the common housefly, of the, I forget how many thousand species of flies on Earth. Flies do very well. Flies are a very successful lineage. They are crushing it. And there are thousands of, you know, it's a very, very diverse group.

39:18And which one of all the offspring of this lineage, which one is the most successful in the only metric that evolution cares about, your genetic replication? It is the housefly, the Musca domestica. What is it about the housefly? Well, you know, 10,000 years ago, from what we can tell, and the history of the fly is patchy, but we can say some things. It's nothing. It's just a little, another member of one of thousands of, you know, nameless fly species.

39:48And it does its thing. It fights for carbohydrates out there in the world. It lays its eggs in dung. This seems to be sort of its life strategy is lay lots of eggs, find some warm, putrefying material. It can be dead body. But there's lots of poop on the ground. And they are incredible at finding it. They're incredible at finding it. And, um, they're, they're out there struggling, fighting the same evolutionary game as every other fly. Um, and then we don't actually know exactly where it's an old world species.

40:20Maybe it's, you know, from, from Egypt, maybe it's from, from South Asia or West Asia, but somewhere very early on, it starts playing a slightly different game in that it starts following us around. It starts replicating in our habitats. And it's sort of by dumb luck pre-adapted to be very good at the kinds of environments that we create. And particularly after we domesticate other animals, we've got lots of, um, cattle and

40:52goats and sheep around. There's lots of poop on the ground. We pile it up. And in fact, we, we pile it up on purpose to use it as fertilizer. Um, and this is just like a bonanza for them. And so they, you know, by dumb luck are pre-adapted to, to live well with us. And then they eat our food. They eat any sugar we lay leaving around, uh, any carbohydrate. And, um, and they take off and they go everywhere we go. Um, they're, they're not a domesticated animal. They're not exactly a parasite, although they can carry diseases and they're super annoying.

41:26It's incredibly easy for us to underestimate how common they were until, you know, 100, 150 years ago when there's just a massive campaign to, to conquer the house fly. They're still incredibly successful and prevalent, but that's after a lot of, uh, efforts to get rid of them and their story, you know, think about the effects on global biodiversity. There's one fly that is the, you know, the most numerically successful fly on the planet. And it's because of our history and you can replicate that.

41:56And think of all kinds of animals across all size ranges, you know, from the squirrel in your yard, the Eastern squirrel, gray squirrel is doing really well in this world because it's very good at living in suburban, we feed the squirrels. Yeah. We, we're helping along that path. These, these, uh, they are, they are commensals. They're eating at our table, uh, or in our backyard anyway. Uh, and it, it almost every sort of taxon you can imagine somewhere there's, there's a species that has really taken advantage of human success.

42:28Um, and so in these ways that are kind of unintentional, we're shaping biodiversity. Well, I think this is, we don't need to go in order.

The First Great Homogenization

42:35So let's like skip ahead to one of the big, one of the other big lessons here. When one species like humanity is become so dominant, the overall system kind of simplifies, right? There's like, it's not a world where there's a billion different niches. It's sort of how well you interact with the dominant one that defines how well you do to a certain extent. And maybe that's, uh, you know, again, a better way of thinking about the problem than just counting the number of species or something like that.

43:07But the, the overall simplification of the environment is an issue. Right. And, and I, I like to say that, you know, we can argue about whether or not humans could, or, or, or might trigger the sixth extinction. And that would be really scary. Um, but to me, it's even scarier to think about the first great homogenization, uh, in the history of life. Like, you know, anytime you say in 600 million years of animal evolution, something has never

43:41happened. You ought to pay attention and say what, um, because everything happens over and over, but never before has one species acquired global ecological dominance that, to the extent that we have, and to the extent that one species is capable of creating extremely homogenous ecosystems worldwide. And this includes ways that are obvious, like our food production system. Um, and so there are, you know, billions of cattle, there are billions of pigs, there's

44:16something, and trust me, I've, I've tried to run to ground and, and, um, worried about the FAO estimates, but just taking the FAO estimates, there's something like 32 billion chickens on earth. Um, so it is the most numerous bird on the planet by a factor of 10, you know, it's, it's the dominant bird on, on planet earth. Um, and in millions and millions of years, when some future, uh, whatever, maybe AI, uh,

44:48uh, paleontologist is looking through the strata of earth history and they hit our layer. They're going to say, Oh my gosh, this weird symbiosis of a, of a primate along with the broiler chickens took over the planet. There's so many chickens, it's incredible. And you think of the thousands and thousands of species cataloged and really unknown of birds that have gone extinct, diversity declines both through extinction and through once common species becoming extremely rare and humans and the, the food that they eat, the animals

45:23that we eat, um, become extremely, extremely common. And, and so that's a kind of obvious and intentional way, but then there are maybe less obvious ways because humans are, you know, we're, we love connectivity. We're social animals. We like to trade and travel and migrate. And we've been doing so from, from the very beginning and very often intentionally and unintentionally, this drives homogeneity in the biosphere. Um, and the, the, the big, um, victim has been island biodiversity.

45:58Islands are an important kind of cradle of diversity. They create little, you know, pockets where evolution can test out different pathways. And, um, ecologists created a, I think a powerful metaphor that humans have created a new Pangea, the, the super continent, um, that, that existed in the geological past. In a way we've sort of made the, the entire earth one super continent, um, which has many, many good advantages, but also we should remember what are the unintended consequences

46:31for, for biodiversity and island biodiversity has taken probably the biggest toll, um, as humans have spread. Well, and, uh, in the realm of domestication, we sort of talked about animals, but plants and even fungi, like these are things that the species balance have been wildly affected by the forces of human interest. Yeah. And this book is about animals. I wrote the book before this was a kind of global history of humans and microbes.

47:01Um, it's a really about pathogenic microbes. It's a big history of infectious disease. So I wrote a book with Princeton on microbes. I have not published this winter. It's, it's about to come out on animals. And there is a, there is a third piece of, of what will be a trilogy on humans and plants. So I leave plants out of this book. I have, um, I have a lot of ideas about what that, what that book will look like. It's, it's absolutely integral to the story. And of course it's all connected. I mean, a major, probably the single most important way in which humans have, have negatively

47:35impacted animal biodiversity is through land use change, which means deforestation, the loss of wetlands, usually because of, of damming or flood control and, um, and the transition from wild prairie to cultivated or sown agriculture. And so plant, that means that we're swapping out the plants. We're swapping out trees for fields where we can plant wheat. We're swapping out wetlands for dry land or, or, you know, stable land where we can plant

48:08crops. And it means getting rid of, of wild grasslands for cultivated grasslands, but that's, that's the third volume. Okay, good. We're going to, we're going to look out for that. But again, just to drive home, this is long before the industrial revolution, right? This is not a sort of modern technology thing.

Cities and Whole Scale Land Use

48:25This is just humans inventing agriculture and dramatically changing our ecosystem thereby. Right. And, and I mean, in case it, in case it needs saying, you know, it's not, uh, the, the storyline isn't just humans are evil or bad. I think there are ways in which we're, we're both. Some of my favorite people are humans. Yeah. Yeah. Many, many of mine, but the, you know, but we need to reckon with it. Um, and, and I think it, it gives us true perspective to realize that humans have been altering the face of the planet in very profound ways for thousands and thousands of years.

49:00And then we can take that perspective and figure out what we want to do with it. But you have to start with, with sort of reality and true facts. And the reality is that, that already our abilities as hunters, our, um, partnership with other domesticated plants and animals, um, gave us tremendous leverage over nature. That's only then been amplified by industrialization and sort of modern technologies, including things like chemistry and so on. Well, yeah, let's sort of creep up on, um, the modern age, I guess is, is the invention

49:34of cities, uh, the next big phase transition that we have to think about? Yeah. I mean, cities, cities are kind of, I try and emphasize that cities are distinct from agriculture. And so, you know, agriculture sort of starts roughly 10,000 years ago and spreads slowly, but it's a long time before you have enough humans and you have all the sort of technologies that you need to have cities. Cities usually, you know, go with a different technological package. There's variability, but you often have metallurgy like bronze.

50:09You usually have writing and sometimes it's cities that, that invent writing, but writing is, I mean, I would, I would say writing is one of the two or three most important technologies that humans ever invent. We invent it four times independently and it's sort of a core technology of city life or civilization. You need it to coordinate, to govern, to trade. Um, and so, you know, writing metallurgy, the domestication of new transport animals like horses, you don't have to have horses to have cities and big States and empires, but it helps,

50:43um, quite a lot and these, this package comes together 5,000 to 6,000 years ago, and then you start to get cities. So cities are very distinct from agriculture. It's a different technological package. It's a different social organization and they're much, much more powerful. They, they sort of, yes, they're a phase transition in human capacity to control nature. They let us do things, um, that are not just sort of a kind of incremental increase over

51:17sort of the early farmers. They're really, really a transformation. Okay. I can't let, um, the statement that we invented writing four times independently just go unremarked. Like what, what four times were those who did that? Uh, let's see. Okay. One is the, um, South Asian, um, script. One is in the, um, the, you know, near East, like cuneiform, and then eventually becomes like the alphabet. Um, let's see. One is East Asia. Um, the, sort of the ancestor of what becomes Chinese scripts.

51:49And then one is in the new world, I think. Yeah. That makes sense. I think I got that right. Come on. I haven't, I haven't lectured notes for this, Sean. We come on the podcast. You gotta be ready. Like, you know, we're going to ask you all the questions. I gotta be ready. Fair. It's fair. I, I, I brought it up, but, but, um, but I think that's the current thinking is that it emerges four times independently, which I think is really cool. I mean, that's actually, I think, uh, one of these points that's like deep once you start to think about it, because this is crazy technology.

52:21Um, it language is already our superpower. It's what, you know, that's the great evolutionary transition of humanity. The symbolic language and cumulative cultural evolution. And then writing is like cumulative cultural evolution on steroids. It lets you transmit and store information across time. And it doesn't seem to have been, you know, I mean, I would, I would say that this, the lesson of the fact that it emerges four times independently says that it's not extremely contingent. Like it was, you know, it keeps happening over and over.

52:53We're humans want to store information and they're going to find ways to do it. Um, and it was sort of, uh, it's convergent evolution. Yeah. Okay, good. And then, uh, that helps us get cities. And what effect do the cities have on our ecosystem and all the life forms around us? I think it's, it's, it's, as we were saying earlier, that land use transformation is the single biggest driver. Um, and that means transforming forests into agricultural fields, wild grasslands into farmed

53:30land and, um, uh, wetlands into farmland. Um, and it's really cities that, that supercharge this or civilization, you know, it's the kind of higher level social organization and the technologies that go with it, that dial that up, um, exponentially. And it's, I think it's hard for us to even sort of understand intuitively how vast this change is. So like old growth forests, I point out in the book, they're, they're very hard to get

54:05rid of. Um, you know, it takes, it takes a ton of labor to get rid of a forest full of oak trees that are hundreds of years old. And yet, um, we managed to, to almost completely get rid of them at temperate latitudes. Um, and so like Europe was, you know, had vast old growth forests that are mostly gone by, um, by the time of the industrial revolution.

54:36Um, even by Roman times, they're, they're long gone in the Roman world. It's, um, I, in the book, I have a scene where when Julius Caesar and the Roman legions are conquering Gaul, which is, you know, France more or less. And they sort of come up to the Rhine frontier. They're really struck by what we would recognize as a kind of ecological frontier between Gaul, which is, which is highly urbanized and civilized kind of technologically advanced and beyond

55:10Germany, which is still characterized by smaller scale societies. And ecologically the old growth forests were in some cases still there. And they're struck by that. And they're struck by these animals. I mean, he talks about reindeer and Aurochs. I mean, he, this is now extinct. The wild ancestor of the cattle is gone, but it was still there until 400 years ago. Um, and certainly when Julius Caesar goes there, he looks at an old growth, ancient forest where

55:41you still have animals like these huge wild cattle, um, that is completely gone. And it's essentially gone because of deforestation. And so if we think of civilization from an ecological perspective, what it does is it empowers our ability to, to conduct whole scale land use change. And it does go with the technology, iron, you know, if you're, if you've got to cut down a tree, bronze is better than stone, but iron is better than bronze.

56:12Um, and it's, it's social organization. These are collective enterprises. The same is true of the way we transform wetlands, um, through irrigation. This is a scaling up of human social complexity that lies behind our ability to, to sort of implement irrigation technologies on landscape scales. So it's just sort of a, an exponential dialing up of our power over nature.

56:43There might be a little bit of irony here in that the kind of unlocking of new modes of social complexity is responsible for damaging the complexity of the natural world around us. Right. I mean, there's, there's certainly a correlation, um, you know, it doesn't necessarily have to be that way. And I think for our future, we, we don't want to, um, think of it too deterministically, but yes, there's, you know, you can argue that like cultural complexity and diversification in some ways is fueled by, um, literally metabolizing natural systems.

Invasive Species and the Dodo

57:19Yeah. And, uh, you already mentioned the sort of reconstruction of Pangea, uh, the fact that we trade and move and shuttle different species back and forth. And there's a whole idea of invasive species, which maybe you can help me, uh, get feelings about. Like part of me wants to say the notion of an invasive species is sort of an antiquated one based on the idea that what happened before we came into a region is how it always was and

57:51how it always should be. Whereas in reality, nature is dynamical and the species are always doing different kinds of things. But of course you don't want to oversimplify so that the whole world has exactly the same set of animals in every place. Right. And it is tricky. And, and I think everybody recognizes that it's tricky that people in the invasion biology community and conservation biology community wrestle with this. They worry, you know, does the language even of invasion sort of prime us to, to, you know, think xenophobically about, about organisms that don't belong.

58:23And there's some very legitimate questions there, but it's a very, it's a very scientifically tricky question because there's such a, an obvious risk of importing arbitrary norms of what does and doesn't belong in a, in a given ecosystem. And, and, and exactly as you say, ecosystems, even without humans are dynamic and changing migration, territorial expansion, or just part of the way evolution works.

58:56Um, and so we should recognize all of those things and be cautious. Um, but at the same time recognize that we want to pay a different kind of attention. If humans are agents of territorial expansion, that doesn't make it bad. It just says, okay, we're interested. That's a different cause. And then two, that if it has, um, negative implications for current species diversity,

59:27um, then again, it doesn't necessarily make it bad. Um, but it certainly sort of dials up our, our level of interest and attention to another level. Um, and humans, it, it, it's important because biological invasions are one of the three or four leading causes of extinction on the planet today. I mean, it's up there with all of the biggies land use change.

59:58So deforestation, um, pesticides and chemicals, global warming, biological invasion is recognized by the, you know, by the IPBES, which is sort of like the, the global consortium of, of sort of government recognized international cooperation of biodiversity issues recognizes biological invasion as one of the top five drivers of biodiversity loss. So we do, obviously we have to, with all of the, the complexity of it have to pay attention

1:00:30because it's such a, a major driver. And it has been again for a very long time. Um, you know, take, take for instance, like every, the, what's the most famous extinction of all time. It's probably the dodo. Um, it's a, it's a bird. It's a weird, beautiful ground pigeon, basically. Um, that exists on Mauritius. So in the mass green islands, sort of east of Madagascar and the Indian ocean, the, the Portuguese, and then the Dutch show up in the 16th and 17th century.

1:01:05Uh, and the dodo is there, the dodo is doing fine. It's a real pity that we sort of like say, go the way of the dodo. And we mean, um, to sort of go extinct because you were obsolete. Um, the dodo is doing perfectly fine. Evolution is very creative. It's adapted to its niche. It's adapted to its niche. Those islands are way out there. There's not many mammals. There's really no mammals except, uh, some bats. And so evolution made a mammal out of a bird.

1:01:38Um, the dodo is basically a, a mammal that happens, a bird that lives like a kind of mammal lifestyle. Um, and it's doing perfectly fine till we show up and there's the, the dodo, I bring up this case because it experiences all of the mechanisms by which humans impact biodiversity. We're killing and eating it. We're changing its habitat. But my, my hunch would be that it's mainly a victim of invasive species because when the

1:02:09Portuguese and Dutch show up, what comes with them? Well, other animals that we bring, and this means black rats, which are a nasty commensal rodents, um, that love to eat bird eggs. Um, we bring, um, certain kinds of monkeys, um, crab eating macaques. Uh, we bring cats. Um, some of these are intentional. Some of these are unintentional, but we introduce, you know, we introduce goats. We introduce monkeys. We introduce cats.

1:02:40We introduce rats. Those four alone and pigs. Sorry. I should have included pigs because pigs are not, I mean, pigs are nasty animals. They're omnivores there. They do very well on their own. The, the feral pigs in Oklahoma are unbelievable. Um, and they eat everything. They eat bird eggs. Um, and probably what happens to the dodo is invasive species. Um, it's all of these things, but you know, the most famous species extinction sort of in history, if you, if you grant the dodo that status is because of invasive species.

1:03:13Um, and it's just sort of a reminder of how powerful it is when you introduce animals to ecosystems, it changes things. It affects things in ways that are predictable and unpredictable. And it's one of the most important ways in which we impact the biosphere. And we do it so rapidly, so pervasively because we're such a mobile species. We love to move. Um, we like to take things with us. So very often, you know, we import exotic plants and animals. People have dumped pigs and goats on islands as long as we've had pigs and goats, uh, because

1:03:45they do really well and because we want to eat them and they usually spell a lot of trouble for, for endemic animals. So, um, invasive species are, you know, all around us in ways that we forget how weird the, the distribution animals that we now take to be normal are really very often the result of human introductions, which again, aren't necessarily always bad, but would judge them by their, their consequences. I used to live in Los Angeles and there are palm trees everywhere.

1:04:18And I was shocked to learn that palm trees are not from around that area. Yeah, no, we've been, we've been moving plants around just as much for sure. And yeah, the, so I, that's, that's very helpful because I would have said the usual elementary school story that human beings came and shot all the dodos, but, uh, it's more like the, it's not individual humans with their guns, but the whole idea of humanity and all of the retinue of humanity that ended up with that extinction happening.

1:04:48Exactly. It's, it's the retinue. I like that. And okay.

The Great Acceleration and Synthetic Chemistry

1:04:52So, and then now we do get to real climate change, right? I mean, the kind of climate change that accompanies the industrial revolution, et cetera. Uh, I have the feeling again, not as a super expert that the talk of the sixth extinction about how human beings are causing so many species to go extinct is largely tied with some combination of pollution and climate change. Well, yes. Although I would say again, it's all of it. Um, and in some ways, you know, the industrial revolution is the most important revolution,

1:05:28the most important transformation in human life since agriculture. And in ways you can think the shift from foraging to farming and from farming to industry are really the, the two revolutions in the way we relate to, to nature and the industrial revolution is, you know, in some ways it's, it's a product of the enlightenment, the scientific revolution and the enlightenment. We start to discover how nature works faster and faster.

1:06:01And then we apply this knowledge to technologies, um, that use resources like coal, um, and then eventually hydrocarbons that give us new sources of, of energy that we harness to machines to, to do work. And this supercharges sort of every mechanism through which we impact the biosphere. It supercharges land use change because now we have more powerful tools to, to cut down trees and to, um, convert landscapes over to farming.

1:06:31It rapidly increases the, the problem of invasive species because now we don't have to rely on, you know, wind power to move us across oceans. We have steam power, we have railroads to move us across land. And so as we move more, and as we move faster, we're moving other animals around faster and faster, uh, as well. So the, in many ways it supercharges the kind of ancient longstanding mechanisms by which we affect biodiversity, but then it creates new ones.

1:07:05Um, and one is, one is climate change, um, which, uh, the, the biggest effects of climate change, anthropogenic climate change on the biosphere are unfortunately still ahead of us. Um, it's starting to matter. Um, but for the most part, the, the worst is yet to come. Um, and it's important to underscore that even though the, the earth's climate changes all the time, climate change is natural, anthropogenic climate change.

1:07:35One is anomalously rapid. Um, and two for the, the purposes of this story is very different from natural climate change and its impacts on biodiversity through the past in that now we're here and all of these other challenges are out there and climate change lays on top of that. Normally if the climate shifts, it does so, you know, fairly slowly and organisms can adapt, they can move, they can migrate. There's nowhere to go.

1:08:06Um, they're, they're against a wall. And, um, when you then start changing the earth's climate, uh, it's, it's a greater threat than it's, than it's ever been. So climate change is a novel threat on top of all of the ancient ones. And then separate from that. And I think one that, that I think we don't think about historically, I don't think we think about it right. Um, this is kind of one of my, my pet, um, themes as a historian, we don't realize how weird the power of synthetic chemistry is from an ecological and evolutionary perspective.

1:08:42It's very recent. You know, it's only about a century old that we've really had the power, particularly for organic synthetic chemistry to, to like build molecules that, um, do things biologically. Um, and it's really like from an evolutionary perspective, it's a very, very weird set of powers and, um, it, it changes the material environment. You know, we're all probably familiar with sort of the environmental impacts of plastics and plastic waste.

1:09:12Um, it's very rapid from a historical perspective. I think what you gain is a sense of how unbelievably fast and novel it is. And then the, the ability to synthesize, um, you know, nitrogen or reactive nitrogen that we can use in ammonia for fertilizer, um, is unbelievably important for our ability to impact the biosphere. And then our ability to, to manufacture pesticides is unbelievably important in its impact on

1:09:46nature, on biodiversity. And that's from a historical perspective, very, very new. Right. And so historians, um, like John McNeil, who's an environmental historian is very good historian. Um, used the term, the great acceleration. And if you look sort of at long run historical change, the, the inflection point is the middle

Exploiting Marine Ecosystems

1:10:12of the 20th century where you have all of a sudden massive global population growth, explosive global population growth, combined with the ability to change the material environment, to synthesize plastics and fertilizer and pollute and pesticides, um, that have, you know, look like the hockey stick, um, graph where the, the last two or three generations represent a startling advance in our leverage over the rest of the natural world.

1:10:45So as, as important as the deep story is, one of the reasons why it's valuable is because it does help us recognize how the kind of power that we've obtained is only a few generations old. Um, we're still sort of living instantaneously in the moment of its creation. We don't know what its ramifications will be. Um, but it gives us a sense of, of hopefully, um, a kind of sense of perspective that, that encourages us to, to be very cautious and to think how radical in the history of life it is

1:11:20for one species to have this kind of power. It, it does remind me the discussion of climate change and, and biodiversity and extinction. We, we should say something about the oceans, because I think there's a lot of action going on there that is maybe hard for us to see. Is, is there some truth to the idea that, uh, hidden from our everyday view, there's a lot of biodiversity being damaged because of the oceans heating up or just changing in different ways? Yes. Yes. And it is part of the, the story that we've been talking

1:11:53about. Um, it is maybe not quite as ancient as some of the other, you know, areas of, of human impact. Um, it's not 10,000 years old, even though our, you know, our ancestors were very eager to adapt to and exploit aquatic resources. Humans have always sort of exploited the riches of, of aquatic environments, both freshwater and, and marine. Um, and yet we were kind of limited. I mean,

1:12:23we're a terrestrial species, our technologies, um, you know, weren't good enough to, to make a huge difference, but somewhere in the last millennium that changes. And, um, you know, there's no one particular moment. I talk in my book, uh, about the history of whaling because it's kind of a microcosm and it's one that you can trace the history of because whaling is amazing. And, um, anytime, anytime we've engaged in it, you know, it's sort of been romanticized and mythicized, but the,

1:12:56the history of whaling is kind of a microcosm of this story. Humans have, have opportunistically exploited, you know, dead whales or near shore whales for a very, very long time, but somewhere around 500 years ago, commercial whaling really starts to, to ramp up and it's off the west coast of Europe where you have a kind of feedback loop between, um, markets that want whale oil. So they're mostly killed, not for, for meat, but for oil, um, in a world where they, they just want, they just

1:13:32want to read at night. They want light, um, like any of us and, um, other kinds of, you know, tallow and, and olive oil and so on are rare and expensive. And, and whales have lots of blubber that you can render into oil and turn into light. And so markets incentivize ever larger operations to, to kill whales. And the, the whaling industry ramps up hundreds of years ago. Um, and really by the time you get to Moby Dick, it's sort of the end of this, this world in some ways of, of sort of primitive whaling.

1:14:07And, um, and it has huge impacts on ocean, on marine ecosystems. Um, and it's, it's telling too, because our impact on the oceans is not really measured by extinctions. I mean, actually humans have driven very, very few marine species to extinction that we, that we know of. Um, but we have nonetheless had massive impacts on marine biodiversity, um, through our exploitation of marine resources. And

1:14:41it starts with, with whales as well as, um, as well as herring and cod, which become commercial industries where hundreds of years ago, we start, um, we start scaling up our extraction of marine resources in ways that start to reverberate throughout food webs that leave simpler impoverished, um, food webs. We, we fish large fish, um, predatory fish out of ecosystems all over the world over the

1:15:12last few hundred years. And then in the 20th century, there's a, an absolutely a great acceleration of fishing, um, where once you get, um, steam driven, then diesel driven, um, fishing boats with massive trawlers and huge, huge nets, um, industrial fishing is truly capable. Well, well, we don't drive many, if any fish species to extinction, we radically impoverish marine ecosystems.

1:15:42Um, and then again, these sort of, these impacts lay upon one another. Now, um, human driven climate change is starting to impact ocean ecosystems. In some ways, that's where some of the most important frontiers are partly because the oceans absorb heat partly because of the, the way that ocean, so many of the ocean ecosystems are tied to coral reefs, which are sort of like the, the, um, tropical rainforests of marine ecology. They're like this supporting their animals, but they're the supporting under like undergirding of so much ocean life. And they're particularly

1:16:19affected by, by climate change. Um, so marine ecosystems are absolutely a huge part of this story. I think it's one that doesn't go back thousands of years in the same way that some of the, the parts of human impact do, but goes back further than, than people think, um, and should be extremely concerning because our, you know, it's easy for us to underestimate how much the earth system, how much our economies and human wellbeing depends on diverse, functional flourishing marine

The Cautionary Tale of Whaling

1:16:48ecosystems. The story about whale oil does remind me that there is another thing I wanted to mention before we wrap up, which is there's sort of a physics centric version of this story where we talk about energy and how it's stored and how it's transferred from place to place and how this is the backbone of all of these transformations we're talking about, uh, using animals, domestic animals to plow our fields or, uh, have different ways of storing caloric energy in food.

1:17:20Yes. Yeah. I mean, you know, energy and, and information are the, the fundamental ingredients of human history too. We learn, we store information, we pass it on, we accumulate knowledge of the natural world. Um, and this empowers us. And then we're always limited by, by energy and, um, we find new ways of, of, of harnessing, extracting, uh, exploiting it. The whale story though, is I think is a good one for,

1:17:51for cautionary reasons too, because humans then in the 19th century, we figure out much more efficient ways than whale oil, um, kerosene lamps and, and then, um, you know, incandescent light bulbs, um, replace any need we have for whale oil, but it's a cautionary tale because do we stop hunting whales? Uh, no. In fact, we invent the, um, grenade harpoon, uh, and get better and better at launching whales. And we keep finding, as we learn how to build new things, new technologies, we keep finding new reasons why we

1:18:24need whales. You can turn whale oil into soap. And in fact, the byproduct of making soap is glycerin, which we figure out how to turn into nitroglycerin. And we make whales into, uh, bombs, into dynamite. We make, uh, whale oil makes very good, uh, margarine. And so a huge number of whales are killed and turned into, to a butter substitute, uh, for, for humans who just want animal fat. Uh, and then it turns out that whale oil is extremely good because it's, it's temperature stable at both

1:18:55high and low temperatures. And so it's perfect for, um, keeping your automatic transmission, your transmission fluid, um, running. And so it's one of the main ingredients in transmission fluid until the endangered species act in 1973. Um, so, you know, we, we advance, we find new and better ways. We find new ways of, of, um, extracting and using energy more efficiently. But if you don't value, um, biodiversity, if you don't value animals, then there's, there's often new temptations,

1:19:26new reasons why we might exploit it. So the whales, the whales are a cautionary tale down there. And the only reason we stopped killing whales is because we decide to, we passed the endangered species act. Um, we develop international conventions, uh, to agree to stop mostly, um, killing whales and whales. We stopped from most species of whales were, would have been in much greater danger of extinction. If we didn't just say, we value this, we value them for their own sake. We're going to decide not to do this. So there's kind of a, there's a little positive, somewhat positive ending to that story where it's not that we stop needing to kill whales to,

1:20:00to make money. We just decide collectively that we want to value them and we change course in the nick of time. I think that is, maybe that's a good final place to go. Um, we start with human beings dramatically changing their environments because they can cooperate, right? They can socially overcome animals much bigger than them from mastodons to whales for that matter. Uh, but there's the prospect that we could agree to be better stewards of the planet that we are living on, or at least figure out what it would mean to live on the planet in a less damaging way.

1:20:34So what do you think, what are the prospects, uh, for us trying to do a little bit better? I mean, is it how, how high, high priority is it?

Valuing Biodiversity for the Future

1:20:42Well, you know, this is the point where I like to say I'm a historian, not, not a futurist. Um, but you know, the past is, uh, you know, you can find, uh, examples that are very depressing, but also, uh, examples that are, that are inspiring and remind us that, that we do have the capacity to, to solve problems collectively. And that it's, that it is up to us. Um, in some ways, you know, I think as a historian, I do think we're going to continue to, to grow as a species.

1:21:12We're going to advance in our knowledge of nature and we're going to build new technologies and we're going to need energy. Um, and so I wouldn't feel too optimistic about, um, human consumption or energy use going down in any, um, foreseeable future, but what we choose to value matters. And, um, I think that's the, that's the positive lesson from Wales and otherwise is that we are, it's a matter of whether or not we, we decide to, to value biodiversity, both for our own sake, for our

1:21:42own wellbeing. We have every good selfish reason to want the earth to be full of really rich, diverse, uh, food webs, but then just, uh, even beyond selfish reasons to say, we want, um, to live in a world where the earth's natural systems are allowed and to flourish in their places, you know, for the same reason we want to have big natural national parks where you can, um, admire a world that's different from the ones that we construct in some way that's just sort of, um, you know, irreducible, it's valuable for its own sake. And so, um, that to me is the key. That's what motivated

1:22:17me to write the book is to kind of evoke some of the, the lost worlds that aren't in some ways, you know, irreversible and some of it's not coming back. Um, and it's not written to, to judge or condemn people who were hungry, uh, people who are very often poor, people who didn't understand the consequences of what they were doing, but we can't say the same. We live in a world where, um, we can be very aware of the consequences of what we're doing and that creates different responsibilities, but history can, can evoke some of the lost worlds, um, and can help us appreciate how profound our change is. But I don't think that has to be, um, sort of paralyzing or

1:22:49demoralizing. It can just inspire us to, uh, be honest about where we are and what we've done. And, uh, affect the way we choose to shape the world as we go forward. Well, I do, when possible, like to end the podcast on an optimistic note. So, I mean, is there any connection to your earlier work on, uh, early Christianity vis-a-vis the Roman Empire and how a different moral ethical system really can change how people live? Not to say that I think that

1:23:20there's one on the horizon, but in principle, we could decide that this is much more important to us than we have been treating it so far. No, absolutely. I mean, the, the power of, of moral systems of, of progress, um, you know, I think the history gives, gives inspiring examples where the, one of the stories of, of Christianization is that, um, the Roman world was very bleak and dark and that it chose not to recognize some people

1:23:52as, as human beings created by God and Christianity, um, helped to change that. I'm a big believer in the enlightenment. Uh, and, um, you know, we're, we may not sort of, uh, change, uh, as a species individually in our sort of inheritance, but as collectively we progress, we learn to, to respect others, to respect the natural world. And, um, so there, there is hope that, um, that may not feel hopeful right at this exact moment in 2026, but, um, I, I like to say I'm a, I'm a pessimist in the

1:24:26short term, but an optimist in the long term. Um, usually we have to learn lessons the hard way, uh, but, uh, but I am optimistic that, um, that in the long run we'll, we'll wake up and, um, and change course in some ways. Being a pessimist in the short term and optimist in the long term is much better than the other way around. That's right. That's good. That makes me, I'm gonna count that as an optimistic ending. So Kyle Harper, thanks very much for being on the mindscape podcast. Thanks so much, Sean.