Speaker 1Hello, 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. But the precise extent to which species go extinct is not known. But the precise extent to which what's going on right now is best described as a new massive extinction event is slightly controversial. And longtime 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. And 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, understanding the physics and biology of the Earth on which human beings live should be an important part of history. And 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. And 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 happening, and then, you know, what is going on. And 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. Kyle Harper, welcome to the Mindscape podcast. Hi, Sean. I'm a big fan of Mindscape. 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 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. Tell us a little bit about how you get from A to B.
Speaker 2Right. 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 pick for good reasons, but also with some negatives. But I was very fortunate to go to a Ph.D. program in history where I was really encouraged to cultivate my interest in the natural sciences. And 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. And 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's system. And 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. And 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, archeological 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.
Speaker 1I think you have mistakenly piqued my interest here. How much? How much ancient DNA do we have? Like how many ancient Romans have we sequenced their DNA?
Speaker 2Yeah. So I can tell you 10 years ago, that number was zero. And 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 population. 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, the number is quickly, quickly growing. And 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.
Speaker 1Is there anything in particular that we've learned that has surprised you a little bit?
Speaker 2Oh, there've 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. I 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. 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. It becomes a Latin speaking province. And we have in 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, 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, of this Danubian provincial capital. There's nobody from Italy. Like we can't find traces of the, the genomes, you know, and even in subsequent generations, you'd expect like, cause a lot of these people are from. Second, third, fourth century. And 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, 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. And like, we don't understand this now. It's the slave system. It's probably capturing people. We know the Romans have lots of slaves, but like, we don't actually really know. really have a good understanding right now of how so many people from Anatolia and Syria end up everywhere in the Roman empire. Um, and so that's kind of a hot question that really we weren't asking before. So yeah, there's lots of, lots of cool new knowledge that we're grappling with.
Speaker 1Well, it gets into another question I wanted to ask because, um, like already in the, the early, your early work on Rome, you were also talking about the natural world, you know, with plagues and things like that. Right. But 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?
Speaker 2Well, yeah. And of course, like I say, we'll, we'll find out with more genomes too, but, but I think that absolutely is, has to be a big part of the answer. Yeah. I think that's a good point. I think that's a good answer. And, and it really like, I'll go back to the point I made that it's hard to explain like all of the, 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. Um, and they're sort of like more Roman than the Romans. And now, 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. You know, they, they worship the Roman gods. It's a deep, deep transformation. And I guess
Speaker 1there'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 is going to be 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.
Speaker 2Well, the good news is that's going to keep historians employed for the foreseeable future. Human societies are complex and, um, you know, we all have our, our pet theories and it usually goes back to whatever you're, you wrote your dissertation on. Um, but, but that's the good thing about human societies is they are, they're the most complex thing we know of. And so many important dimensions from geography to, um, the gods that they worship that are, that are actually important for questions that you might really want
Speaker 1to ask. And so what is it that, um, particularly made you think, you know, we, I have to understand how humans are affecting the biosphere.
Speaker 2Yeah. 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. And 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 seventies 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 texts 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. And so when you read an ancient text, you're sort of sensitized to, to see things that maybe weren't as, you know, leaping off the page in the same way for previous generations. It's that, that we're, as I said before, we're learning new things and as a historian, you know, you're always, 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. But 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. And, okay.
Speaker 1So 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, 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.
Speaker 2Right. And we've been doing it for a very, very long time. And it was a, it was marine ecologists who came up with the, the term shifting baseline syndrome, which is the kind of natural, both human and scientific tendency. You want to measure something. So you, 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 up too much on this, but like, it's actually a really interesting question and an open question. When do humans start to influence the climate system? Yeah. Because there are serious, you know, 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 sort of still contested in the field, but I think the human impact on biodiversity is, is actually less ambiguous. I mean, we have been influencing, you know, climate change, climate change, climate change, 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, 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. And so the story of how we've impacted biodiversity goes back easily to the Pleistocene.
Speaker 1Well, let me ask one of those questions. It sounds super simple to ask what 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, okay, it's humans doing this work now?
Speaker 2Yeah. I mean, it's a, it's a great question. And, uh, my, my colleagues in anthropology will probably fact check me, but there's a, there's a, an analogy that, um, that, um, Richard Wrangham uses in his book, catching fires, the Harvard primatologist anthropologist that I use with my students when I'm teaching kind of a big history course, or, or sort of like moving through the first few million years of human history that, um, in, in some sense, Australopithecines are apes that we would sort of think of as not human, but members of the genus Homo are, 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, uh, without, without too much question. And so, you know, that means that we're looking at, you know, 2.6 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, um, is making tools controls fire has symbolic language. Um, and really you would feel like this is a human. And so sometimes anthropologists will talk about archaic humans, um, to refer to these species that are us, but not fully us, not Homo sapiens, but are like human. You 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, um, creative, um, beings. And the more we learn about our sort of sister species and later, um, so-called archaic humans like Neanderthals, the more like us, they seem. So the, the human history is probably more than 2 million years old. Um, and you know, Homo sapiens, our species looks to be more like 300,000 years old. So yeah, when we say human, it's, it's, it's less, uh, less easy and less transparent than we might automatically expect.
Speaker 1But my impression is that, and I, 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?
Speaker 2Yeah. I mean, yes. And in fundamental terms, that's accurate. And of course it's hard because, you know, we, we, as somebody who's, who's, uh, spent a little bit of time worrying about, you know, how many humans were there in the Roman empire, which is like yesterday. Um, we, we still like debate about that Really, fundamentally, and people disagree about it, when you go back before there are 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 people debate about how many humans there are at the Pleistocene-Holocene transition a little over 11,000 years ago. But it's probably on the order of 5 to 10 million Homo sapiens. By that time, there's only us. 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 Okra. Gloma, across the whole globe. So, we know that all humans until 10,000 years ago are fundamentally foragers. They 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.
Speaker 1And 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.
Speaker 2Right. 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. We emerge in this highly variable ice age of a climate epoch. And we spread out of Africa fairly early, at least by 100,000 years. People are immigrating and exploring. And 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. When humans move out into the world. They are moving into a world where terrestrial biomes. So we're on land. The ecosystems are dominated by big animals. And that's not just sort of like an aesthetic point. It's not like, cool, it's a safari. 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. They, it's not like one or two species here and there. The 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, 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. But the Pleistocene is dominated by ecosystems where big animals rule.
Speaker 1And 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.
Speaker 2Yeah. And I think it's important to, like, try and. 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. But it sort of captures. It 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. Again, 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, you know, so it's not a huge number of species relative to the total number of mammals or even total number of humans. It's not a huge number of animals that exist. In fact, it's a rounding error in terms of the number of animal species on the planet. But 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. Sort of like a species on the landscape. They are the integral cog in the ecosystem. They 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. And 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.
Speaker 1Tell 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?
Speaker 2Yeah, it's complicated. And there's a huge, I mean, there's a debate that's been going on for hundreds of years. I mean, I, in my book, I quote the sort of the father of geology, Charles Lyle, who comes to America, actually 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, you know, visiting in the 1830s and he's talking about how, you know, remarkable it is that so many enormous animals lived so recently. And 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. I mean, every organism faces environmental challenges when the environment changes, vegetation bands shift, the food sources. 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. Wolves 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. And but wolves are kind of weird already because they cooperate. And so it's sort of 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 tool makers 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 throwers autolautals and then eventually bow and arrow and 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 um and you know nothing nothing hunts an adult mammoth um and and then we do and um they're not used to it big animals tend to reproduce very slowly they tend to have smaller populations um and so they're kind of vulnerable to this the shock that is is represented by the introduction of human hunting so we're social tool making predators and then you know we we also control fire i suspect this is kind of underrated because it's archaeologically very hard to get at but humans use fire um in in hunting we know that we do this today we do this um in in more recent centuries using fire to drive big animals um into traps or into bogs or into ravines or over cliffs um and it lets us um cooperate to hunt really big animals and to kill in mass to kill large numbers of of individuals simultaneously and then if all that wasn't enough um 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 um and we domesticate dogs and um this is you know like the new york yankees and boston reds are i should say los angeles dodgers now i'm a red sox fan but it'd be like if the yankees and dodgers were like let's let's team up um and just form one super team and it's very hard to say because again the archaeology doesn't provide direct evidence um exactly how important dogs were but it's very hard to say because again the archaeology doesn't provide direct evidence so it's very hard to say but um 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 to partner with your biggest rival um who is a natural born killer wolves was or not the most obvious friends uh but they become our best friends literally uh you know man's best friend and um that seems to sort of be a part at least of the the sort of hunting and hunting prowess of early humans it's kevin
Speaker 1durant to the warriors right oh you had to do that come on that hurts we will never forget or forget around that i know the oklahoma city fans that's okay you turned out okay in the long run um but i love that point because i think that when people think about humanity's effect on the biosphere etc they think of machines in the industrial revolution burning coal and and what have you but just our ability to socially cooperate gave us this leverage far beyond our muscular ability early on
Speaker 2yeah it did and um fire is fire is already you know a most 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 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 the air and 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 the watershed after that really is domestication so it's not just wolves becoming dogs but then we enter into the natural world and we're in a natural world but then we enter into this strange multi-species alliance with ibexes that become goats mouflon become sheep aurochs become cattle boar become pigs um it'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 and but for a very long time and so yes the industrial revolution is a is a breakthrough but we'll miss uh an important part of our impact if we don't have that deeper perspective and that perspective matters for for the world around us but the you know the megafaunal extinction at the end of the ice age in evolutionary time is still contemporaneous um and then you know that that's literally just just um inseparable in a way that's just so important to us and i think that's what's so important to us in evolutionary time and we um and the world you know is still responding to that in some ways and then we intervene in that world but we intervene ever faster and faster do we
Speaker 1know when human beings started using fire no
Speaker 2anthropologists debate it and the challenge again is archaeological because the you know 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 you know lightning you know it's hard to say whether this represents controlled fire or is this um that started a fire and so it's it's debated by by anthropologists who who study homo erectus i mean i think the the consensus is going to be sometime around a million to five hundred thousand years ago maybe closer to a million it gets into questions too about human evolution um 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 um digestive systems our mouths are pretty pathetic i mean for a predator for a carnivore you know what we have pathetic uh dental equipment um and so they there's there's debate about what's the role of fire what does that tell us because we can actually follow easier in the fossil record human evolution changes to the you know cranium and the body and um that lets us infer sort of that maybe fire was around uh but it's indirect evidence so uh it's it's 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
Speaker 1good uh so let's let's go back to the domestication domestication because i don't think that we're done there i learned a new word from your book commensal commensal uh commensal yes commensal when you haven't quite domesticated you're just like sharing a food ego system with the local species and that might lead to bigger things down the road
Speaker 2yeah 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 the etymology is sharing a table that's what commensal means in latin um and it means ecologically a species that isn't quite a symbiont and isn't quite a parasite it's somewhere in between um and it's taking advantage of the the ecological effects of another organism it's sort of writing the tales um of another organism and it's a pretty loose um 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 but it's possible to say we domesticated these animals um 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 right that's our domesticate but that 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 and this is true of a really shocking range of of organisms and one that that i love thinking about is the the house fly in some ways um its story sort of captures the the human story musca domestica the the common house fly of the i forget how many thousand species of of flies on earth flies do very well flies are a very successful lineage um they they are crushing it and there are thousands of you know it's a very very um diverse group and which one of all the offspring of this lineage which one is the most successful and and the only metric that evolution cares about your genetic replication it is the house fly the musca domestica what is it about the house fly well you know ten thousand years ago as from what we can tell in the the history of the fly is 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 and it does its thing it fights for carbohydrates out there in the world it lays its eggs and dung um this seems to be sort of its 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. Um, 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. Maybe 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 goats and sheep around. There's lots of poop, 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. It's incredibly easy for us to underestimate how common they were until, you know, a hundred, 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. It's because of our history and you can replicate that and think of all kinds of animals across all size ranges, you know, from the, 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 backyards. We feed the squirrels. Yeah. We, uh, 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. Um, and so in these ways that are kind of unintentional, we're shaping biodiversity.
Speaker 1Well, I think this is, we don't need to go in order. So 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 and 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. But the, the overall simplification of the environment is an issue.
Speaker 2Right. And, and I, I like to say that, you know, we can argue about whether or not humans could 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. You know, anytime you say in 600 million years of animal evolution, something has never happened. 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 something, and trust me, I've, I've tried to run to ground and, and I'm worried about the FAO estimates, 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, uh, 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 that we eat, um, become extremely, extremely common. 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 big, um, victim has been island biodiversity. Islands 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 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 for, for biodiversity and island biodiversity has taken probably the biggest toll, um, as humans have spread.
Speaker 1Well, 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.
Speaker 2Yeah. And this book is about animals. I wrote the book before this was a kind of global history of humans and microbes. Um, it's really about pathogenic microbes. It's a big history of infectious disease. So I wrote a book with Princeton on microbes. I've not published this one or 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 impacted 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, 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 crops. And it means getting rid of, of wild grasslands for cultivated grasslands. But that's, that's the third volume. Okay, good.
Speaker 1We'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. This is just humans inventing agriculture and dramatically changing our ecosystem thereby.
Speaker 2Right. 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. And 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.
Speaker 1Well, yeah, let's sort of creep up on, um, the modern age, I guess is, is the invention of cities, uh, the next big phase transition that we have to think about?
Speaker 2Yeah. 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 you 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 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 um quite a lot and these this package comes together five thousand to six thousand 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 sort of the early farmers they're really really a transformation
Speaker 1okay i can't let um the statement that we invented writing four times independently just go unremarked like what what four times were those
Speaker 2who 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 and then one is in the new world i think yeah that makes sense like i think i got that right come on i haven't we're not gonna let your notes for this sean we come on the podcast you
Speaker 1gotta be ready like you know we're gonna be ready questions i gotta be ready fair
Speaker 2it's fair i i i brought it up but but um but i think that's the 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 um it language is already our superpower it's what you know that's the great evolutionary transition of humanity symbolic language and cumulative cultural evolution and then writing is like cumulative cultural evolution on steroids it lets you transmit and 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 humans want to store information and they're going to find ways to do it um and it was sort of it's convergent evolution yeah
Speaker 1okay 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
Speaker 2us i think 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 land and um wetlands into farmland 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 rid 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 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 um even by roman times they're they're long gone in the roman world it's um i in the book i have the 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 germany 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 right is gone but it was still there until 400 years ago and certainly when julius caesar goes there he looks at an old growth ancient forest where you still have animals like these huge wild cattle 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 got to cut down a tree bronze is better than stone but iron is better than bronze um 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
Speaker 1there 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
Speaker 2mean 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 don't want to 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 literally metabolizing natural systems yeah and
Speaker 1uh 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 how it always should be whereas in reality nature is dynamical and 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
Speaker 2and 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 and and 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 uh and exactly as you say ecosystems even without humans are dynamic and changing migration territorial expansion are just part of the way evolution works um 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 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 um 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'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 so deforestation yeah 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 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 because it's such a major driver and it has been again for a very long time um you know take take for instance like every 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 masquerine 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 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 was 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 um 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 portuguese and dutch show up what comes with them well other animals that we bring and this means black rats which are a nasty commensal rodent 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 we 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 they're 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 um and it's just sort of a reminder of how powerful it is when you introduce animals to ecosystems it changes things it changes the ecosystem it changes the ecosystem 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 right people have dumped pigs and goats on islands as long as we've had pigs and goats because they 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
Speaker 1live in los angeles and there are palm trees everywhere and i was shocked to learn that palm trees are not from around that area yeah yeah now we've
Speaker 2been we've been moving plants around just as much for sure
Speaker 1and yeah the so 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
Speaker 2exactly it's it's the retinue i like that
Speaker 1and okay so and then now we do get to real climate change right i mean the kind of climate change that accompanies the industrial revolution etc 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
Speaker 2change 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 the 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 and then we apply this knowledge to technologies um that use resources like coal um and then eventually they 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 convert landscapes over to farming it 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 do 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 long-standing mechanisms by which we affect biodiversity but then it creates new ones um and one is one is climate change um which 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 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 one 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 right um 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 it'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 do things biologically yeah um and it's really like from an evolutionary perspective it's a very very weird set of powers and um it changes the material environment you know we're all probably familiar with sort of the environmental impacts of plastics and plastic waste um 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 nature 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 he's a 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 of 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 that have you know look like the hockey stick graph where the the last two or three generations represent a startling advance in our leverage over the rest of the natural world so 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 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 for one species to have this kind of power it
Speaker 1does remind me the discussion of climate change and and biodiversity and extinction 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
Speaker 2in different ways yes yes and it is part of the the story that we've been talking about um it is maybe not quite as ancient as some of the other you know areas 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 aquatic environments both freshwater and and marine um and yet we were kind of limited i mean we're a terrestrial species our technologies um you know weren't good and we were kind of limited and we were kind of limited 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 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's amazing and um anytime anytime we've engaged in it you know it's sort of been romanticized and mythicized but the the history of whaling is um kind of a microcosm of this story humans have have opportunistically exploited you know dead whales or 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 want 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 and 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 the surface of the ocean um and it's it's it's been a very very long time since we've ever had a 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 it 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 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 last 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 um 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 Oceans absorb heat, partly because of the way that so many of the ocean ecosystems are tied to coral reefs, which are sort of like the tropical rainforests of marine ecology. They're like this supporting their animals, but they're the supporting undergirding of so much ocean life. And they're particularly affected by climate change. 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 parts of human impact do, but goes back further than people think and should be extremely concerning because it's easy for us to underestimate how much the Earth system, how much our economies and human well-being depends on diverse, functional, flourishing marine ecosystems.
Speaker 1The story about whale oil does remind me. 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, using animals, domestic animals to plow our fields or have different ways of storing caloric energy in food.
Speaker 2Yes. Yeah, I mean, you know, energy and information are the fundamental ingredients of human history, too. We learn, we store information, we pass it on, we accumulate knowledge of the natural world, and this empowers us. And then we're always limited by energy, and we find new ways of harnessing, extracting, exploiting it. The whale story, though, I think is a good one for culture. Cautionary reasons, too, because humans then in the 19th century, we figure out much more efficient ways than whale oil, kerosene lamps, and then, you know, incandescent light bulbs replace any need we have for whale oil. But it's a cautionary tale because do we stop hunting whales? No. In fact, we invent the grenade harpoon and get better and better at launching whales. And we keep finding as we learn how to build new things. We keep finding new technologies. We keep finding new reasons why we need 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 bombs, into dynamite. We make whale oil makes very good margarine. And so a huge number of whales are killed and turned into a butter substitute for humans who just want animal fat. And then it turns out that whale oil is extremely. Extremely good because it's temperature stable at both high and low temperatures. And so it's perfect for keeping your automatic transmission, your transmission fluid running. And so it's one of the main ingredients in transmission fluid until the Endangered Species Act in 1973. So, you know, we advance. We find new and better ways. We find new ways of extracting and using energy more efficiently. But if you don't value biodiversity, if you don't value animals, then there's often new temptations, new reasons why we might exploit it. So the whales, the whales are a cautionary tale down there. And the only reason we stop killing whales is because we decide to. We pass the Endangered Species Act. We develop international conventions to agree to stop mostly killing whales and whales. We stop 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. make money. We just decide collectively that we want to value them and we change course in the nick of time.
Speaker 1I think that is maybe that's a good final place to go. 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. 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. So what do you think? What are the prospects for us trying to do a little bit better? I mean, is it how high priority is it? Well, you know, this
Speaker 2is the point where I like to say I'm a historian, not a futurist. But, you know, the past is, you know, you can find examples that are very depressing, but also examples that are that are inspiring and remind us that we do have the capacity to solve problems collectively and that it's that it is up to us in some ways. You know, I think as a historian, I do think we're going to continue to grow as a species. We're going to advance in our knowledge of nature and we're going to build new technologies and we're going to need energy. And so I wouldn't feel too optimistic about human consumption or energy use going down in any foreseeable future. But what we're going to do is we're going to continue to do that. And so I think that's the that's the positive lesson from whales 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 own well-being. We have every good, selfish reason to want the earth to be full of really rich, diverse food webs. But then just even beyond selfish reasons to say we want to live in a world where the earth is full of rich, diverse food webs. And so I think we're going to continue to grow as a species. And to flourish in their places, you know, for the same reason we want to have big natural national parks where you can admire a world that's different from the ones that we construct in some way that's just sort of, you know, irreducible, it's valuable for its own sake. And so that to me is the key. It's what motivated me to write the book is to kind of evoke some of the lost worlds that aren't in some ways, you know, irreversible, and some of it's not coming back. And it's not written to judge or condemn people who were hungry, 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 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 and can help us appreciate how profound our change is. But I don't think that has to be sort of paralyzing or demoralizing. It can just inspire us to be honest about where we are and what we've done and affect the way we choose to shape the world as we go forward.
Speaker 1Well, 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 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 there'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.
Speaker 2No, absolutely. I mean, the, the power of, of moral systems of, of progress, you know, I think history gives, gives inspiring examples where the, one of the stories of, of Christianization is that the Roman world was very bleak and dark and that it chose not to recognize some people as, 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 short term, but an optimist in the longterm. 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.
Speaker 1Being a pessimist in the short term and optimist in the longterm is much better than the other way around. So that's right. That's a good, that makes me, I'm going to count that as an optimistic ending. So Kyle Harper, thanks very much for being on the Mindscape podcast.
Speaker 2Thanks so much, Sean.
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