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

Sean Carroll (0:00)

Hello, everyone. Welcome to the Mindscape Podcast. I'm your host, Sean Carroll. You may have heard that species of life forms 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 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, 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, the 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 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, 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.

Kyle Harper (3:53)

Hi Sean, I'm a big fan of the show. Thanks for having me.

Sean Carroll (3:56)

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 started writing books about ancient Rome. That's what historians are supposed to do. We understand that. That's history, ancient Rome.

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.

Kyle Harper (4:31)

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.

To tell it in personal terms, I, as a student, as an undergraduate, loved both the humanities and the sciences. When you go to graduate school, you have to pick for good reasons, but also with some negative consequences. But I was very fortunate to go to a PhD program in natural history, where I was really encouraged to cultivate my interest in the natural sciences. 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 consider natural science fields are helping us understand the human past. 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. 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. For those of us who are, say, in Roman history, 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. As a historian, I really not only just have a natural inclination for the sciences, but have benefited from the fact that there's all kinds of cool new data. 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. As a historian, that was my pathway into environmental history, a kind of history that tries to understand our place in the natural world, that it's partly humanistic, but it's partly scientific.