Today, I have the pleasure of chatting with Kyle  Harper, who is a professor and provost emeritus  

at the University of Oklahoma, and the author of  some really interesting books: The Fate of Rome,  

Plagues Upon the Earth, Slavery in the Late Roman  World, and an upcoming one called The Last Animal. 

The reason I wanted to have you on is because  I don't think I've encountered that many other  

authors who can connect biology, economics,  history, and climate into explaining some of  

the big things that have happened through human  history in the way you can. The most recent  

reason I wanted to have you on is I interviewed  David Reich, the geneticist of ancient DNA, and  

some of the questions we were discussing, he kept  emphasizing this overwhelming and surprising role  

that diseases have had in human history, not just  in the recent past, but in his work going back  

thousands of years, tens of thousands of years. He said, "You gotta have Kyle on." I emailed  

him afterwards, asking "Who should I interview  next?" And he said, "You gotta have Kyle on". 

You have this graph in The Fate of Rome. You show human population over the last few  

thousand years. I assume that these two  downspikes are both the bubonic plague,  

Yersinia pestis, right? Yeah. 

And so this is not like some small little  nudge you can see, the overwhelming —I mean,  

other than the hyper exponential growth in human  population— the overwhelming, not just one,  

but the overwhelming two major features in human  population going back the last 10,000 years,  

is this one bacteria, right? Yeah. 

One of the things you discuss in the book  is that the collapse of the Roman Empire  

was a result of this one particular event. The period that I normally work on is from  

the High Roman Empire, the glory days of the  Pax Romana in the first or second century,  

through what we call the late antique  or early medieval period, the sixth or  

seventh century. At the beginning of this  period, Rome dominates this Mediterranean  

empire. It's what you think of when you think  of ancient Rome. It's the largest city in the  

world. It's the center of this huge network. By the end of this period, the city of Rome  

has 50,000 to 100,000 people. It's a tenth or  twentieth of its former size. I think we now can  

say pretty clearly that environmental factors  like climate, but also especially diseases,  

play a part in that really big transformation. While there's a problem because we don't have  

the same kind of modern government mortality  statistics that we do for COVID or even for  

the last century or century and a half, we have  to piece together from clues. But it's pretty  

clear that the bubonic plague events, whether  you're talking about the Black Death of the 14th  

century or the plague of Justinian in the sixth  century, these events are capable of causing  

death rates, temporarily, that are just orders  of magnitude beyond what we're accustomed to.  

Even in these ancient societies, the reason  why these were so shocking, in a world where  

the death rate is always pretty high—probably  several percent of the Roman population, three,  

four percent a year may be dying in a normal  year— for them to just be utterly shocked by  

the death rate already tells you that it's  some multiple of what they're accustomed to. 

Yeah. I think you discuss in the book the  possibility that the death rate might have been  

close to or even over 60% wherever the Black Death  hit. This is literally the most significant thing. 

Yeah. It's mind-blowing. In the case of the Black  Death in the 14th century, it's pretty clear. It  

kills 50, 60% of the population in entire regions.  We don't necessarily think that it killed 50,  

60% of the whole continent, although that's  actually not impossible. But even the fact  

that it's killing 50% of the people  in cities, in provinces, in countries,  

is just beyond the damage that other plagues do. Right. And do you think that were it not for this  

60% mortality event plus the fact that we haven't  even discussed yet, this super severe cold snap,  

do you think that the Roman Empire might  have otherwise just kept going? You discuss  

there were these two previous other big  pandemics. The empire still survives. 

I think Will Durant had this quote that the  Roman Empire fell for longer than most empires  

have lasted. Do you think it'd be similar  to China maybe? Maybe a dynasty collapses,  

but fundamentally, the same sort  of cohesive nation reemerges? 

Yeah. That's a great comparison. Not just decline  and fall of dynasties, but also geographic changes  

in the configuration, that parts get added and  parts get cleaved off, but you still kind of  

think of it as fundamental continuity in the core.  That to me is a very plausible counterfactual. 

Justinian, the emperor in the 540s—he reigns from  the 520s to the 560s—he’s on a path of success.  

He's retaken Africa. He's mostly retaken  Italy when the plague hits. To me, a very  

plausible counterfactual is that a more or less  Mediterranean core of the Roman Empire could have  

survived east and west. It does sort of survive in  the east, but even including really all of Italy,  

Africa, and probably Spain. That would have been  a very reasonable outcome of the sixth century  

if you hadn't had this kind of random shock. The Roman Empire would keep going. Remember,  

it does, and it calls itself the Roman Empire  until the 15th century. But we would think  

of it as maybe more the Roman Empire if it  still included the western Mediterranean and  

was this major, powerful, urbanized polity  that resists invasion from the southeast,  

as happens in the seventh century. So the answer  is yes, I think that the Roman Empire absolutely  

could have had another turn as the thing we  kind of mean when we say the Roman Empire: this  

pan-Mediterranean, powerful, urbanized empire. Yeah. Okay, one of the things I found really  

interesting was you were discussing the  firsthand accounts as this big —and feel  

free to explain the cold snap as well as  it's happening— but the firsthand accounts  

of people who are experiencing this, some of  whom come from this burgeoning Christian faith,  

which already lends itself to millenarianism and  apocalyptic thinking. I'm curious basically how  

did different people try to make sense of this  once in a 1,000-year event that's super intense? 

Clearly, people have to try and explain, within  the elements of a worldview that they have,  

how something like this could happen. They don't  have modern science. They don't have germ theory.  

They don't think of it in terms of a biological  event or climatic event. Since that's come up and  

you've invited, I'll say a little bit about that.  This is one of the other really exciting frontiers  

where we're learning new things about the human  past that we just didn't know 10 or 15 years ago. 

In this case, we now have really cool paleo  climate data that helps us understand that this  

period of the sixth and seventh century  was also a period of really abrupt and  

significant natural climate change. We're all  familiar with anthropogenic climate change,  

that carbon emissions stay in the atmosphere,  trap heat. Humans are changing the climate.  

That's a big problem and we can talk about  it if you want. I just want to clarify,  

that view is not incompatible with the  reality that the climate does also change  

for natural reasons on every timescale, from long  geological timescales to much shorter timescales. 

We live in the Holocene. The last  11,700 years have been pretty stable,  

pretty warm. It's an interglacial. We're  literally between Ice Ages right now. It's  

been really stable in the big picture. Yet even  within that stability, there are smaller scale  

climate variations and climate changes. Because  we need to understand how the earth system works,  

how the climate system works in order to  be able to model what's happening, we need  

an empirical record of what the climate has done. For historians, this is great news because now we  

have a huge number of sometimes even pretty high  resolution climate reconstructions for historical  

periods across the Holocene. We now know, like  we did not know this 20 years ago when I started  

graduate school, that the Roman period experienced  some really abrupt episodes of climate change. In  

this case, the sixth century, we know the cause:  there was a series of really significant volcanic  

eruptions. Volcanoes are a very powerful  short-term climate forcing mechanism.  

They eject sulfur into the stratosphere. It  aerosolizes and creates a reflective shield that  

scatters the radiation entering the atmosphere. It leads usually to short term cooling. In this  

case, you had a series of really significant  volcanic eruptions that cooled the climate for  

several decades. In some ways, the later series  of eruptions even like a century and a half. It  

wasn't just a little bit cooler, it was like a  degree to two degrees cooler, which we all kind  

of know now: two degrees isn't weather, this is  climate. Two degrees doesn't affect your day, but  

two degrees globally is a pretty different globe. All of a sudden in the late Roman world,  

it's much, much cooler. Probably areas that have  been wetter are now drier. Places that are drier  

may be wetter. It changes the hydrological  cycle as well, which is more complicated. In  

addition to the shock of the plague, you have  this simultaneous and probably not unrelated  

shock to the climate system. We know that it was  essentially challenging for agriculturalists.  

When the sun is blocked and it's really cold and  the wheat doesn't grow, your society then starves. 

The Romans get this wham bam double  shock of climate change, famine,  

and plague. So back to how people explain this.  Apocalyptic thought is one of the principle ways  

people frame it. To them, nature's going  crazy. Huge amounts of the population are  

dying of this horrible sudden disease and the  crops don't grow. You don't have microbiology  

and you don't have climatology. So you explain  it with the resources of the worldview you have. 

There's a huge burst of apocalyptic  thought in the sixth and seventh century,  

which is always kind of there. You mentioned  that Christianity is eschatological. It is,  

yes, fundamentally, but that comes out in  different ways with different emphases in  

different time periods. This is a period, the  sixth century, when there's a really sharp  

emphasis on eschatology in Christian thought. I found your early chapters in the book about  

what the Roman economy was like in  this happy period quite interesting.  

There's a bunch of questions I have about  this. If you read Gibbon, writing in the 1770s,  

I think he says that the happiest time in human  history was this period you're talking about. That  

was true at least according to him as of a couple  centuries ago. This was still peak civilization. 

You discuss the complexity of the Roman  economy. The fact that millions of tons of  

wheat and other products have to make their way  to Rome and the trade networks and everything.  

You basically say they were experiencing  productivity gains. The wages were increasing,  

population was increasing, but they were still  not at the level at which it was plausible that,  

say, for these climactic and biological factors,  they might have had an industrial revolution. I'm  

curious why you think... paint a picture for me of  what the Roman world looked like as of this happy  

period and why that still counterfactually  couldn't have just saved us a thousand  

years of history if they were on the right track. First of all, I think this is the sort of question  

that historians ought to worry about all the time:  why didn't the Roman economy catalyze the takeoff?  

In some ways it was so precocious for its time  period, and it seems not utterly impossible. The  

Roman world is still a pre-industrial economy so  agriculture is the dominant sector. The majority  

of people work in agricultural pursuits  and productivity is low. They don't have  

modern mechanized traction. They don't have modern  synthetic fertilizers. They don't have the modern  

green revolution yields, all the things that  have made agriculture stupendously productive. 

The primary sector is fairly limited in  terms of its productivity because of the  

limitations on technical inputs. We can think of  the inputs to an economy are going to be capital,  

labor, and ideas. What the Romans have  is people. They have some investment,  

but they don't have technology. They don't  have ideas. It's a late Iron Age civilization.  

I do think there's productivity growth and  that productivity growth comes from markets,  

from trade where you get comparative advantage. In Egypt, I'm really good at growing wheat.  

You can make glass in Syria. And then  we'll trade. The urbanization of the  

Roman world certainly facilitates that.  Cities are these hubs of productivity  

and exchange. There's some technology. If you  look really hard over five or six centuries,  

there's certainly economies of scale where the  production process and manufacturing is moved  

from artisanal to industrial scale. But there's  no takeoff because they don't have science. 

They don't have research and engineering that  drives continuous productivity gains. I think  

they go precociously far in a pre-industrial  setting where you take trade really far. They  

have good institutions in terms of strong  property rights. There's relatively reliable  

contract enforcement. There's financial markets.  They have the most advanced financial markets in  

the world before the 17th or 18th century.  There's impersonal financial intermediation. 

It's not like you have to know me and come  ask me for a loan if you wanna build a ship  

and go trade something. There are banks that  take money from depositors, keep balances,  

and then lend out to debtors who want to go  and do entrepreneurial things. They have so  

much potential, but there's no spark. You never  see these sustained productivity increases. I  

would just say ultimately it's because the  Romans don't have technology improvements  

that are really self-sustaining. The reason they don't have that is  

because they don't have science. Their science  sucks. I'm offending some of my colleagues,  

I'm sure. Galen is great. Ptolemy's incredible.  I love Pliny the Elder's encyclopedia, but if you  

look in the big picture, the contribution that  the Roman Empire makes to our knowledge of how  

nature works and then the applied technology that  comes out of that is really pathetic for five, 600  

years. They go as far as you can with Smithian  advantages to market exchange and specialization,  

to banks and finance. But without the  kind of creative destruction of new  

technologies that improve productivity, you're  eventually gonna run out of improvements. 

If you're Augustus or some other  Roman emperor and you're like, "Look,  

we've got this big good economy, but I wanna  see productivity gains," and you wanna make  

it happen somehow, is there something from a top  down perspective you could have done? In Britain,  

the government subsidizes the royal arts  and so forth and the Longitude Prize. 

That's exactly what I was gonna say. This  happens first in France and then Britain,  

but you get royal societies for science where  you're doing really... I would say there's like  

three things that are essential there. One is  the promotion of what we would call basic or  

fundamental science. It doesn't all have to  be immediately practical or commercialized.  

But you're promoting deep knowledge of nature. Two, you're doing it in an empiricist way. This  

is something very important in the 17th century  that the Romans by contrast don't have, is the  

spirit of Francis Bacon that we need to ground  our knowledge in experiment and observation,  

not just believe whatever authorities  or Aristotle said. That's very much the  

spirit of places like the Royal Society:  we don't take things on anybody's word,  

especially Aristotle's. You need basic science.  You need empiricism, rigorous and self-correcting. 

Third, you need a sense of useful knowledge,  and that's the other thing that really comes  

together in the 17th century: not just the  basic and abstract science, but the application,  

and the 17th century language for that is  useful knowledge. That is something that  

doesn't ever get wired together in the Roman  Empire. There are tinkerers and engineers,  

but they're not talking to the mathematicians and  the physicists. If you were from on high to design  

self-sustaining innovation, I think you would want  to bring those elements into proximity. Augustus,  

unfortunately for them, didn't do it.  Probably good for the world. The Romans  

are pretty nasty people in a lot of ways. I definitely am of the opinion that the  

high science matters, that Isaac Newton is  not a tinkerer. He's not building pumps.  

But the guys who are are his friends.  They're in and around the Royal Society,  

and they're absolutely... Look at Denis Papin,  who was a French engineer who was very much in  

the circle of Leibniz and the very high abstract  mathematics, trying to build vacuum pumps. 

The proximity of high math, high science, very  abstract with what is ultimately gonna be the  

sectors that lead to mechanization where then  you can harness this source of energy that is  

there all along but hasn't been tapped in coal.  That's what catalyzes the big positive cycle of  

positive feedbacks. What the Romans don't have  is that. What the Romans do have is the kind of  

specialization, and now that we look for it,  it's there. When you look at food processing,  

which is a huge sector, the way that  they built mills, there's definitely  

improvements. But there's never the catalytic  change where you get runaway positive feedbacks. 

That's right. A previous guest of mine,  Nat Friedman, I don’t know if you saw this,  

launched this challenge called the Vesuvius  Challenge. This library at Herculaneum in 79  

AD was buried under the ashes of Mount Vesuvius  when the volcano erupted; speaking of volcanoes.  

Now they figured out with modern techniques how  to read the burned scrolls and it is supposedly  

the biggest library of classical text ever.  It would double the amount of classical text  

we have. As a scholar of ancient Rome, what  would you personally find most fascinating?  

What are you excited to find from this data? I'm super interested in the history of math.  

What happens after Euclid? It's very hard to  say because you get these really interesting  

people that pop up, like Diophantus who's  later, in the early Roman Empire. There's  

still really interesting math going on. Euclid  is incredible. The Greek experiment in math  

and science is the one that I think had the  better chance of sparking sustained takeoff. 

And it didn't. It'd be interesting to know more  about why. Why did things stall? Because these  

people... Euclid is not just a towering genius  who comes out of nowhere. He's very much a product  

of the culture and the questions that are being  asked in the generations before. It just sort of  

feels like after him, you fail to get that kind of  sustained continuous progress and advance. Maybe  

back to that big question that we were asking  before: what prevents the kind of breakthroughs  

that we see in the modern world? What is the population of  

Greece during their golden age? Of the greater Greek world or individual  

city-states like Athens? We think of Athens  as being a couple 100,000 people. Not massive. 

So I wonder if the Greeks had the science  but not the people to sustain a modern  

economy. Or not modern, but even a  sort of industrial economy. And then  

the Romans had the people but not the science. Yeah. There's probably something to that, that  

there's just not the critical mass of educated  people, of sheer cognitive power to keep it going.

Let's turn to another one of your books, the  one about slavery in the Roman world. I did not  

realize before I read that one how much Rome  was a slave society. I guess that just isn't  

a salient thing in a conventional understanding  of Rome. Why don't you paint us a picture of how  

much slavery was involved in that world? Slavery tragically is a really important  

institution throughout history. We sometimes tend  to think of it as a distinctly modern phenomenon,  

but that actually misses the deeper picture.  In fact, it obscures the importance of modern  

slavery because modern slavery is uniquely  important and it's uniquely tied up with  

certain kinds of market exchange and certain kinds  of production, certain kinds of racial ideologies.  

There are things about modern slavery that are  really important to understand are different,  

but not just because slavery is there. Slavery has this longer history and slavery  

is more important in some societies than others,  and we want to try and understand that, to ask  

why and then what implications does that have  for understanding those societies? Rome is one  

of those societies. Slavery is really a prominent  institution in Rome from the late republic. As the  

Romans conquer other parts of the Mediterranean,  they start taking captives as slaves en masse,  

and they build an economy that really relies on  slave labor in important sectors of the economy. 

Plantations where commodities like wine,  olive oil are produced for market exchange  

that allow landowners to amass enormous  amounts of wealth. Slavery becomes this  

really important institution that's entangled  in the development of the Roman economy from  

maybe the third or second century BCE, and  then with ups and downs and really important  

changes along the way for centuries and centuries. So you're pointing towards from the supply side,  

all the Roman conquests lead to all this  surplus labor that they can make use of,  

and on the demand side, these cash crops. Exactly. I'm very big proponent of the idea  

that you have to have both. You have to have  a source of slaves. After the conquest stops,  

the Romans figure out other sources of slaves. If  anything, the demand is equally or perhaps even  

more important because if there's not a mechanism,  if there's not institutions that let you  

turn this kind of exploitation into cash flow, the  institution's not gonna go very far. It really is  

the institutions, the presence of markets  where you can take labor and turn it into  

profit that's the most important element. One of the things I find interesting is  

in the age of colonization we're used  to thinking about slavery in terms of  

race but also religion and other things which more  obviously demarcate free and slave populations.  

In the Roman world, it doesn't seem that that's  clearly the case, yet there's no abolition  

movement the way that emerges out of England  in the 19th century or maybe even before that. 

The reason that's mysterious is, if you were  literally descended from slaves, if you were like,  

"My grandfather was a slave but then we were  freed," and they're basically just like you,  

you would think that there would be more  of a sense of... not everybody would be an  

abolitionist, but at least some people  would be writing about abolition. With  

Christianity and so forth burgeoning, they  didn't seem to have a problem with it. Why  

is there no abolition movement despite the  heterogeneous nature of the slave population? 

It's sort of disturbing in a way, isn't it, that  humans have the ability to convince themselves  

that it's okay to own other human beings  as property through a variety of different  

kinds of ideological justifications. You see  even in the ancient world there are different  

models that people use to say that slavery's  okay. Aristotle develops a theory of natural  

slavery that actually some people deserve  to be slaves by their very nature and that  

it's actually good for them to be in bondage. What's really interesting though is that that  

doesn't actually ever seem to be the dominant  ideology. The Roman ideology of slavery is not  

racialized. It's not like the Romans think that  the Greeks or the Germans are some fundamentally  

separate kind of human that justifies their  exploitation. The Roman ideology of slavery  

is really rooted in the law of property and  status. They think that slaves are people who've  

been conquered and rather than killed, they've  been spared, and they've been sold into the  

condition of being somebody else's property. This seems to mentally explain to them  

where their slave system comes from and why  it's justifiable. You have different kinds  

of criticism of the slave system from within,  but remember, most of what we have written is  

from the slave ownership class. I don't think the  slaves were themselves believing this ideology,  

and there must have been sort of what we would  think of as abolitionist movements or spirit  

that we just don't have really good records of. It is this curious thing that the Romans are able  

to build this huge system that's really brutal  and really violent, but has this kind of flimsy  

ideology where they tell themselves these stories.  The deeper lesson of that is that humans can  

create these systems of belief that will exclude  others and justify almost any form of exploitation  

and convince themselves that it's okay. I hope your next book about The Last  

Animal discusses the potential  parallels with factory farming. 

There's some... there's a pretty  gruesome chapter, I'll say that. 

I don’t know if you mentioned, what numbers  you say, I think it was like 10 to 20% of the  

population under the Roman Empire was enslaved.  Given that large a size of a slave population,  

it's surprising to me that there are  so few slave revolts not only in Rome,  

but even throughout history. There's Spartacus  in 71 BC, then there's the Haitian Revolution.  

If 20% of the population is enslaved, how is  this sustainable? If you're running a farm and  

there's 4,000 slaves and then the next farm over  also... why aren't there more slave rebellions? 

Why not? How did they do this? They have  a really elaborate system of repression.  

They're worried about it. Probably the parts  of Roman society where there are 20, 30,  

40% slaves are pretty limited to certain  regions and certain time periods. Partly  

because once you cross some kind of threshold,  the challenges of repressing direct violent  

resistance… It's a system of exploitation. That  means there's always a mix of carrots and sticks,  

to put it crudely. The Romans extract people's  labor partly through physical violence, but also  

partly through systems of manumission that try and  incent people to obey and not to rebel in order  

to earn their freedom. They're using everything  from literal chains to enticements to try and keep  

rebellion from ever coalescing in a way  that can turn into collective violence. 

It's a little bit challenging for us to look  back. We know in Pompeii, the slave population  

is huge. It must be 30%. Not all of these people  would've been plantation workers who were lashed  

every day and worked to the physical bone. A lot  of them are nurses and textile workers and maids  

and tutors and all sorts of things that are  sort of quasi-embedded in households as well,  

where there's always this weird psychological  dimension too. Part of the strangeness of  

slavery is how deeply embedded in  domestic institutions it is as well. 

There are ideologies in which the paterfamilias is  sort of the father and the master. That tries to  

brainwash people against resistance. The important  thing to recognize is it's just a pervasive system  

that tries to colonize people's minds and  pervasively tries to keep them from resisting. 

I wonder if we can close the loop  with the question we began with,  

which is, why didn't Rome have an industrial  revolution? I don't know if it's a plausible  

explanation that cheap slave labor reduced the  incentives for mechanization and engineering  

and other crafts or if not. I don’t know. It's definitely an argument that's been  

made. Aldo Schiavone was an Italian historian who  argued that. It's kind of a neo-Marxist tradition  

that argues this. It's an interesting argument.  I don't buy it at all. The good version of that  

argument would just be that the Roman Empire  is using slaves in many of the most forward  

elements of the economy too. We tend to think  progress and economic growth and innovation  

is good, and we know slavery's bad, so we tend  to think that those things don't go together. 

But in reality, it's the most economically  advanced sectors of the Roman economy  

that had a high degree of organization and  productivity that tended to employ slaves.  

In the Roman world, you could make the argument  that if the labor in those sectors had been free,  

there would've been more opportunities  for positive feedback loops. The way the  

argument's usually made is just that the  Romans got rich without really thinking  

about productivity. They just wanted to extract  labor, extract wealth rather than create wealth. 

That's not a terrible argument, but ultimately I  don't think it's the system of labor that keeps  

the Roman world from industrializing. There are  lots of sectors in the Roman world where slavery  

is not a dominant institution, and it's not like  they're more productive or flirting with some  

kinda breakaway. So it's an interesting argument,  but not one I've ever found all that persuasive. 

Final question about Roman slavery. What  did Gladiator get right and wrong about?  

Would they just abduct you in front  of your house and make you a slave? 

You mean the first one? The first one got right  that when you're making a movie you should worry  

more about making a good movie than a certain  amount of history, but actually the first one's  

a great movie. If it was completely historically  accurate, it would've been much more boring. So  

I'm not gonna be critical of that movie. It plays  very loose with the facts of high politics around  

Commodus and the creation of this character.  But who cares? Russell Crowe's incredible. 

But on slavery in particular. On slavery in particular, I think actually that's  

one of the strong suits of the movie. You see this  completely exploitative system that brings people  

from very different parts of the world who have  very different backgrounds. The system of urban  

spectacle is very real. The use of slave labor  in that is certainly a part of it. So the movie  

actually gets some really important things about  that right. That makes it totally forgivable that  

it has to create a kinda high politics storyline. Okay, I think that covers all the questions about  

Rome. We can get back to your most recent  book about human history and plagues. 

What do you make of the general argument that  people have often made that we were living in  

a sort of Eden before agriculture? Especially  given you've explained that all these diseases  

that we're sorta stuck with are actually quite  new. If we take that perspective seriously,  

was life before human population  exploded and we had agriculture  

just much more pleasant, at least in comparison? Homo sapiens is 200,000 to 300,000 years old. We  

emerge in Africa and disperse, multiply, but  we spend 90, 95% of our history as foragers.  

People who are hunter-gatherers, who  take energy from wild food sources,  

rather than sedentary farmers who've domesticated  plants and animals and live a sedentary lifestyle  

where you're enslaved to this wheat or rice,  but it gives you reliable calories. That is  

along with the Industrial Revolution, and then  whatever this thing we're about to go through,  

the biggest change in the history of our species. The shift from foraging to farming affected  

everything. It affected our beliefs. It affected  our genetics. We're all basically genetically  

different, adapted to live in a different kind  of environment with different kinds of diets. It  

affected our societies, it affected inequality,  it affected culture in every possible way,  

and of course it affected our health in really  basic ways. It affected our labor regime; doing  

the same kind of labor over and over every day is  very different from running around as a hunter,  

chasing deer or whatever, which sounds quite nice. It changed our labor regimes. It changed our diet,  

most of all. Hunter-foragers tend to  eat high protein, high fat-ish diets,  

with no refined carbohydrates, but limited carbs.  It's a very varied, highly varied diet. Sedentary  

farmers tend to eat more monotonous diets and they  tend to be dependent on grains and starches, so a  

very narrow spectrum for your calories. Changes  in labor regime, changes in the diet, and then  

changes in lifestyle, being sedentary and living  in big populations that then puts you in proximity  

to other humans, puts you in proximity to human  waste. Feces are a major conduit of infection. It  

puts you into proximity to the air they breathe,  which is conducive to respiratory diseases. 

This transition, which takes thousands of  years, is more of a process than an event.  

It has massive implications for human health,  including the infectious disease environment  

that we inhabit. It's not like hunter-gatherers  were living in paradise. The infectious diseases  

that they had were seriously burdensome,  they sucked, and probably most people died  

of infectious disease. Malaria is a really  old disease. Lots of diseases existed in  

the Pleistocene, in our Paleolithic past. It's not like it was Eden. There is this idea that  

the transition from foraging to farming... Jared  Diamond called it humanity's biggest mistake.  

Certainly these changes entailed some things  that were not net positive for humanity and  

one of them is that it definitely increased  the infectious disease burden. Simply as our  

population multiplies and as we're in contact with  feces and as we're sharing the air through which  

respiratory pathogens can spread, diseases  are constantly trying to take advantage of  

this. That's just how nature works. Energy is  scarce. Everybody's trying to steal it from  

everybody else, including microbial parasites. The disease burden of humans over time definitely  

increases. The burden of infectious disease on  humans goes up over time. Very broadly across  

these thousands and thousands of years, the  diseases suffered by people by the time of the  

Roman Empire are absolutely much worse than  what had been the case in Stone Age times. 

James Scott has an interesting theory in Against  the Grain. I don't know if it originates with him,  

but he argues that one of the reasons that the  early agriculturalists were so successful... And  

David Reich, if you've seen his stuff about The  Yamnaya 4,500 years ago conquering all of Eurasia,  

but before them, the Anatolian... the initial  farmers are the ones who displaced the initial  

hunter-gatherers across Europe and Asia. He argues that initial wave was so successful  

because of these first diseases that the farmers  had created the conditions to engender. Basically,  

the relationship these farmers had with respect  to the foragers they were taking over from was  

similar to the relationship the Europeans had  to the Native Americans, where inadvertently,  

the disease is just a significant player  in why you were able to dominate them. I  

don't know how plausible you find that. I mean, first thing, it's important,  

I think you were starting to get at this, that  there's never a generation of humans that has the  

opportunity to make this choice once and for all,  like, should we stay hunting mammoths or should  

we become sedentary farmers with basically  torturous dentistry and die by diarrhea?  

This happens over thousands of years through an  evolutionary process where nobody can... It's a  

story of unintended consequences. The mammoth  are gone partly because we killed them all. 

People start... the first livestock that  are domesticated are goats. Nobody says,  

"Hey, let's become goat farmers." The goats  are wild. They're ibexes. People are hungry,  

and so they start managing them to only kill  the males to make sure that they can reproduce,  

and they start penning them and they start  killing the wolves who are trying to attack  

them. Over very long periods of time, this  becomes this tight mutualistic relationship  

where all of a sudden we're goat farmers. But no  generation makes that whole decision for anybody. 

That's part of it, is that it's unintended  consequences that are made in very incremental  

steps. Two is, I definitely agree that there's  some kind of cultural selection here where  

the farming groups are simply so much more  adapted to extract energy efficiently from the  

environment. It's all about energy. You want to  multiply, you want to grow, you want to survive,  

it's all about energy. Foragers require huge  landscapes to extract enough energy to feed  

themselves and grow and reproduce, whereas farmers  per unit of land can extract such higher rates of  

energy that then can be, through photosynthesis,  turned into edible sugars that we can metabolize. 

Those populations are just growing faster,  that they quote unquote out-compete the  

hunter-gatherer population say of Europe that  are largely but not completely displaced. Now,  

on top of that, just the energy story alone  is a big piece of it, but then on top of that,  

you probably do have some kind of population  difference in the exposure and possibly even  

immunity to infectious diseases. I definitely  think that early farmers, the first farming  

societies that are starting to live sedentary  lifestyles where you have aggregations—these are  

not cities, these are villages—but still,  that's more than a hunter-gatherer band. 

Your childhood is then going to be constant  exposure to a series of pathogens. Those kinds  

of populations, when they're then migrating  into Europe, are probably carrying these  

pathogens with them that may have had a kind of  further effect that on top of just being able to  

extract more energy and multiply faster, drives  up the mortality of the existing populations. 

Yeah. The point you made about fertility is  interesting. I vaguely remember reading that  

it's not just the fact that the energy density is  lower, it's that you're also moving around a lot.  

Because of that, you're spacing out kids  much more so than if you were just in the  

same place. I think the actual fertility for  foragers is sort of like reasonable—I don’t  

know if sustainable is the right word because I  don’t mean in an ecological sense but more so—it  

keeps your population constant. Yeah. Don't make me swear,  

but it's like more like four than six.  Because women who are moving with the  

foraging bands miles and miles on foot  on average a day, and also carrying kids,  

are gonna have very different life history  than sedentary populations. That's very clear.

One thing I'm really curious about is what  effect these diseases through history have  

had on the cognitive functioning of people.  You discuss this in the chapter about more  

recent history of the great divergence and  probably attributed the productivity of Europe  

that they were able to have public health earlier.  But literally going back thousands of years,  

you mentioned, for example, that Caesar was 5'5"  and that was considered tall during his period.  

Did the same diseases and malnutrition that  caused these physical health effects also mean  

that the average IQ was much lower, because  when you're a kid you're sick and that steals  

away nutrition from brain growth or something? Yeah. Short answer, yes. Long answer, we know  

that in the modern world, say over the last 250  years, first in Western European societies and  

their settler offshoots and then more globally and  more rapidly globally, there have been really deep  

physiological changes in the average human. We're  talking about populations with distributions.  

What's happened is really two things. One is  there's more energy per capita. People eat more,  

they eat more calories, and they eat better  calories. They eat lots of bad stuff too,  

but people eat more. Two, the burden  of infectious disease has been lowered. 

Growth for a human is a very complicated  trait that's influenced by genetics. I  

was never destined to be super tall. But it's  also affected by environment, which includes  

nutrition and what you spend either doing labor  or what you spend fighting infectious disease.  

Infectious disease imposes a huge burden on the  body. The immune system is extremely metabolically  

expensive. If your childhood is spent just  fighting infectious diseases, you're going  

to struggle to invest energy in growth. There's massive increase in the size of  

populations over the last 250 years and even  though it's an even more complicated trait,  

this improves people's cognitive abilities.  People are smarter. May not feel like it—I  

think it has rapidly leveled off—but people are  more intelligent today than they were 100 years  

ago. Their brains are better nourished and their  bodies spend less time fighting pathogens. I think  

there's no doubt that pre-industrial populations,  and again, populations—so you still have your  

Isaac Newtons, who whatever infected him as a kid,  didn't slow him down—but at the population level,  

I think there's no doubt that not only  were pre-industrial populations shorter,  

this is just a total fact that we know from  their bones, but they probably also, on average,  

had a lower distribution of cognitive  abilities. But with a big distribution. 

You have a great profile in the book about  living in London in the 18th century and  

just how disgusting it was. It was pretty disgusting. 

But at the same time, in that city, you were just  mentioning, there are these scientists and people  

with towering intellects who were basically  figuring out how the universe works and how  

to make all these machines and so forth.  One answer is just like what you just said:  

the distribution was lower, but maybe Newton  would have had an IQ a standard deviation higher  

if he was born today. Just seeing that from  the small population, you're seeing so much  

genius. I guess the question is, how could you  have had this much of a deleterious impact on  

cognitive functioning and still had enough spare  geniuses to kick off the Industrial Revolution? 

Obviously, it didn't keep them from discovering  some pretty amazing things. So it couldn't have  

been completely destructive. That's what's  interesting about the early modern period in  

the 17th, 18th century, in particular, is it's  sort of this between period where you have the  

pre-industrial and the modern that are still mixed  together in these really interesting ways. The  

example I use in the book is the very famous diary  of Samuel Pepys, who's this incredible figure and  

is very close to Newton and that social group and  his name is on the first edition of the Principia.  

These people are this close to each other. But the stuff that I evoke, I won't say—this  

is a family podcast—but the stuff that Pepys does,  bodily functions, is mind-blowing to us. It's vile  

and disgusting. But at the same time, right down  the way, you've got people who are making the most  

fundamental discoveries about the nature of  the universe and inventing machines that will  

improve productivity and ultimately economic  output. That's what's precisely so weird and  

interesting about that particular period is you  have this kind of mingling of the old and the new. 

When I had Joseph Henrich on, one of the things he  discusses is if you look at... cultural evolution  

has figured out some remarkable things. If you  look at the cuisines of different cultures,  

apparently the spices they use match the  antimicrobial and antifungal properties you  

need in that particular biome. At the same  time, you’re reading that part of the book,  

I'm like, "Okay, I get in some cases, they just  genuinely did not have the resources to invest  

in public health and so forth". But come on,  you're just like sleeping in your own vomit and  

so forth. Why didn't cultural evolution  or something like foresight just be like,  

"Hey, this we can sort of do without"? It's a deep question and what I think we  

don't think enough about is how, in a really  fundamental way, hard are some problems to  

solve? Some problems are just very, very hard to  solve. Even though the incentive is really there,  

you think, "Ugh, that took a really, really long  time to figure out". Even though if you'd only  

known, it would've made your life so much  better. There's tons of trial and error. 

The example that comes to my mind is the mention  of vaccination. Which is one of the great human  

achievements, like, of all the public health  improvements is the most important one. Public  

health is never perfect. It's this system of six  or seven really critical tools that involve clean  

water, personal hygiene, vaccines, antibiotics,  different kinds of therapeutic interventions  

or rehabilitation therapy. We still can't fend  off all the germs. You have to have all of that  

and you can sort of achieve this equilibrium  state where you mostly have it under control. 

Vaccination's the most important one and it  took forever to find the first vaccine. It took  

this huge period of all kinds of weird trial and  error, like inoculation with the actual smallpox,  

which is very, very dangerous. Not vaccination.  Vaccination uses cowpox, the lymph of an infected  

cow, to intentionally cause the immune reaction  of humans. Before that, people would inoculate a  

person with actual smallpox, which is just giving  somebody smallpox. You do it through the skin,  

but you're giving somebody smallpox. It was absolutely in a utilitarian way,  

the rational thing to do. It had these horrific  death rates. It would never get FDA approval. But  

in a world where 10, 20% of kids die of smallpox,  it's this horrible decision, but you'd be rational  

to do it. We actually don't know where that  comes from. It may come from Africa, it may  

come from China. It spreads for like a century  or more before Jenner discovers vaccination.  

So it's clearly really hard to figure that out. Even after Jenner, it's like another 60 years,  

70 years before Pasteur kind of systematizes it  and says, "Hey, we could do this for everything".  

Some of these discoveries and innovations are  really, really hard to discover. But then the  

beauty of cultural evolution is that we can  store that information, and you and I don't have  

to figure out any of that. We can go on to the  next problem because that's now been collectively  

stored in the library of cultural evolution.  It's known, we don't even think about it  

most of the time until it's controversial.  What a blessing to live after people like  

Jenner and Pasteur who figured that out. There's this great blog post by the author Slime  

Mold Time Mold where it's discussing.... Wait. Author what? 

You don’t know internet culture, you know,  there’s a bunch of weirdos out there. 

I'm in a different world,  sorry. What did you call them? 

Slime Mold Time Mold. You can't just drop that. Like I'm gonna  

let that one slide. Okay. I got some homework. Anyways, they have a blog post about scurvy and  

why it took so long to discover, and he was  discussing all these sort of... it's sort of  

an epistemic conundrum because you can use lime  and you realize, "Oh, it works". But then if you  

use lemons, which have much less vitamin C, or  maybe it's the other way around, they just work  

way worse. Then there are certain kinds of fruit  which have vitamin C, certain kinds which don't.  

It's actually hard to figure out what is it if  you don't have a mechanistic explanation about  

how you solve this problem, and I think they  had once figured it out and then they lost the  

knowledge until it was rediscovered again. But it makes it all the more mysterious  

that the kinds of things that Henrich discusses  forager societies having figured out. Literally,  

there's this 10-step process for how to process a  certain kind of bean so that you don't get cyanide  

poisoning, and if you mess up any one of those  10 steps, you're gonna get cyanide poisoning.  

A society just figures out the right taboos and  traditions to process beans. But you can figure  

that out, but this thing which is causing 20%  mortality, you only get in the 17th, 18th century. 

Yeah. We need to think more about the computation  that's happening. You said it takes like 10 steps  

to figure out how to process this one particular  kind of food, but I'm guessing it is just really  

hard to figure out infectious disease. It's  a really steep mountain. Once you get up to a  

certain plateau, then the discoveries come really  fast. They become systematic, and they become more  

fundamental. But it was really hard to get there. Not that many societies really scaled it,  

not even within the societies that did.  It was just a handful of people at first,  

but they did get there. Okay, and then asking about  

where different countries were at around this  time. What evidence do we have about what was  

actually happening in India before the British  or the Mughals because it does seem to be this  

sort of black box in terms of historiography?  Do we know if there were these huge plagues? 

Yeah, it's such a tricky problem. Start with the  third plague pandemic in the late 19th century.  

We know that that's in India. India's a big  part of its history. In fact, its where the  

plague bacillus is discovered by Alexander  Yersin. It's called Yersinia pestis in his  

honor. A Japanese scientist finds it exactly the  same time. Gets left out of the nomenclature. 

It’s a special kind of honor to  have the deadliest agent in history. 

To be the worst pathogen ever; immortality. The  plague is definitely in India in the 17th century.  

We know that from contemporary written records  that are pretty unambiguous about the presence  

of the disease. What we don't know is was it there  before that? And if not, why not? Because it kind  

of actually seems like it's not. At least not in  this same explosive way. That's pretty curious. 

We don't have a great explanation of that because  India's connected to the Central Asian world  

where the plague is endemic. There's plenty of  trade. It would have plenty of chance to move to  

the subcontinent. So we don't understand that. If  you go back even further, that's the Black Death.  

You go back even further to the late  antique period, it's like a total mystery,  

and the Indian sources from the fifth  and the sixth century are not great. 

They're hard to use. This is totally outside  my language abilities. They require totally  

different expertise. I've worked with some people  who think that there are oblique references  

that may be interpreted as epidemic. One of the  interesting things is we actually think that the  

plague moves through India to get to Rome. This is not definite, but the plague's  

enzootic, its natural animal reservoir is the  Tian Shan Mountains where China, Kazakhstan,  

and Kyrgyzstan meet, and we can actually identify  a pretty small region where the pandemic lineage  

comes from. We know that it doesn't go overland,  so it's not like the Black Death, which goes  

across the steppe, the Mongol trade networks,  military networks carry it. In the sixth century,  

probably, the plague goes south through India,  and maybe the ports in Gujarat or along the  

West Coast that are still pretty connected with  the Roman world, with East Africa, with Arabia,  

with the Red Sea, that the plague travels  on ship across the Indian Ocean, because  

the Plague of Justinian shows up in the Red Sea. That is a clue that it probably is imported on  

this seaborne commerce. But how it got from  Central Asia to Gujarat is a hard question. 

Huh. I know the way we found that the Yersinia  pestis existed in these Yamnaya 4,500 years  

ago is by... Didn't they just find the...? I  don't know how, but if you can figure that out,  

why can't you look at the fossils of people  500 years ago or 1500 years ago and just see  

if they have Yersinia pestis in them? There's two things. First of all,  

you have to look. There is at present not nearly  the same amount of ancient DNA laboratory work  

that's happening on remains from ancient India.  So if you're not looking, you're definitely not  

going to find it and people aren't looking. Secondly, it takes a lot of luck for it to  

preserve. The DNA molecule starts degrading the  second you die, just starts falling apart. Even in  

the best of cases where we're getting it from...  usually, if it's pathogen, you're getting it from  

the dental cavity. If it's human DNA, you're  getting it from the inside of the skull. But  

it takes a lot of luck for it to preserve because  the soil conditions will affect the degradation,  

the temperature will affect the degradation.  Just in a crude sense, heat is bad. That's why  

there's more DNA, ancient DNA, that's preserved  at more northern latitudes so far. But it has  

as much to do with the fact that people aren't  looking. We should be looking, and if you've got  

skeletal materials from an ancient mass grave  in India, call me. We can definitely look. 

And just to be clear for the context- Ancient, ancient, ancient. 

Okay, going forward to the future a little bit,  speaking of future technology, maybe the one  

that's more relevant than AI is synthetic biology,  and there's a worry that you can potentially  

create diseases which... maybe the evolutionary  gradient is one that is not catastrophic where  

diseases are incentivized to be transmissible  but keep you at a chronic level of infection  

that doesn't necessarily kill you immediately.  Actually, it's interesting why the bubonic plague  

diverges from that selection pressure, which  maybe you can answer. What do you think about  

the potential that with synthetic biology people  can make diseases that have the transmissibility  

of measles, but also the deadliness of  something like Ebola? Is that, given your  

understanding of biology and whatever, is that  plausible given your understanding of biology? 

Let me start with the plague where I'm a little  more comfortable and can say something as a  

knowledgeable person. I think it's relevant  because you said it's weird that the plague  

seems to sort of evade some of these evolutionary  constraints, and it's worth saying what these are.  

A pathogen is a disease-causing organism,  a microbe, usually a virus or a bacterium,  

but also fungi and single-celled organisms like  protozoans that cause disease in a host. They're  

not trying to cause you disease. COVID doesn't  hate you. Plague doesn't hate you. It's just  

evolution. It's just trying to steal energy  or hijack your cells to reproduce its genes. 

In fact, it has incentives to try and do that as  well as possible while doing the least possible  

damage. It's always kind of trying to thread  that needle or to find the right balance,  

because if a pathogen just kills you instantly  there's nothing to steal and it can't transmit  

its genes into the next generation. Every pathogen  has these basic evolutionary problems. How do I  

get from one host to the next? And how do I evade  my host's immunity, which our immune systems  

are incredible, for long enough to multiply? Most pathogens have to explore the space where  

there are these various constraints, and they find  all sorts of weird ways around it. Evolution is  

really good and really creative, unfortunately for  us. The tricks that they find to hide inside your  

immune system or to fake it out are really wild.  There are two reasons why plague is so weird,  

and we don't completely understand why plague is  so weird, but I think there's two basic reasons.  

One is that it's vector-borne, which  means that it's transmitted through  

another organism that is the intermediate. Arthropod or insect vectors are really annoyingly  

helpful to certain pathogens, and most... there's  actually a relatively small number of diseases  

that are transmitted through a vector like this,  but they tend to be really nasty, like malaria,  

typhus. They can kind of get away  with it because even if you're dying,  

a mosquito can come and bite you and transmit  malaria to me. Plague is a vector-borne disease.  

It's very well adapted to transmit, particularly  by fleas, but we think also maybe by lice and  

other biting organisms, but really by fleas.  It's really good at transmitting by fleas. 

That's evolution. This is one of the cool things  with ancient DNA we've been able to piece together  

at the absolute molecular level, the genetic  changes that let it make this protein that have  

this effect in fleas. It's really weird, it forms  this biofilm in the gut of the flea that chokes it  

and makes the flea feel like it's starving. So the  flea just starts feeding and feeding and feeding,  

and meanwhile it's regurgitating bacteria. Sorry, can I ask a question about that? Why  

is it the case... 'Cause there are diseases  that hijack the flea's mind or ants' minds  

or something. Why isn't there a disease that  makes humans zombies? Is it just the human  

brain is so complicated that it's like...? Let me come back to this. We can talk about  

zombies, but we need to wind up for that. Okay, so  one, flea- So the plague is vector-borne, and it's  

really good at manipulating the fleas, and it's  just evolution. Two, I said this before, but it's  

an animal disease. We're like collateral damage.  We're totally irrelevant to the really core  

evolutionary history. The plague just wants to  infect rodents. Of course, I'm... it's not really  

wanting to do this. The plague makes a living, it  survives out there in burrowing rodent colonies. 

We're like tertiary. It doesn't care at all. It  has no evolved incentive to modulate its virulence  

to be able to transmit sustainably. Plague never  sustains itself in human populations. It can  

transiently infect human populations, but then it  always dies out. It becomes extinct, that lineage. 

And then what is the reason that you have  these 1,000-year cycles basically? Why  

is it not 500 years? Why is it not 10  years? Why is it not… What causes it to  

go dormant? What causes this to reemerge? You need to ask me in five years because  

we've learned so much and now this is like the  thing that would fall in the category of almost  

a new question now that we can ask. Now that we  have the Neolithic lineages and the Bronze Age  

lineages, we're starting to piece together this  fuller history. But we still don't even totally  

understand the boundaries of when the plague  is really sort of not circulating in human  

populations, and what are the factors  that cause it to be so explosive. Like,  

is it evolution of the bacterium? Is there  something about the genetics of the lineages  

that escape from the animal reservoirs that are  especially transmissible? Is it human ecology,  

like, that we put rodents like black rats in the  right place to get the disease? Is there something  

about the climate stress that renders the  population…? We don't have a great understanding  

of like why the plague comes and goes. That's scary. Connecting it to your other  

question about these superbugs, what's interesting  in the very big picture about the plague to me is  

the history of infectious disease is like, on the  one hand, there's a real core of it that's just  

basic principles of ecology and evolution. We do  certain things in the environment that creates the  

conditions that pathogens can evolve and take  advantage of. But on top of that, evolution  

is just creative and weird and contingent and  unpredictable. It's those little, contingent facts  

that can end up having these really huge effects. In the case of the plague, if you were really  

knowledgeable about the basics of ecology and  evolution of disease, you would never be like,  

"I think that every now and then a rodent disease  from Central Asia is gonna wipe out half of the  

continent". Like, that shouldn't... that's not  predictable. That shouldn't be happening. That  

one's kind of an outlier, but infectious disease  is always kind of like that. Tuberculosis has  

probably killed more people maybe than any  other infectious disease. It's like this  

horrible disease. We don't really understand  it. Now we really don't understand where it  

came from because it doesn't look like it  has an animal host before it has humans. 

It's just a weird disease. It's just a bacterial  pathogen that, in the huge world of bacteria,  

this one is very good at hiding. It gets in your  chest and it just lurks. Then it'll just waste  

you away, particularly if you're poor and you're  stressed. There are some core principles there,  

but then it's just something weird about it.  It's just this terrible luck that makes it  

what it is. To me, there's going to be another  pandemic, maybe bird flu, maybe something else. 

But it's the real outliers and the weird ones  that we should maybe worry about a little bit  

more than we do. If you want to go to zombies,  I'll go there. You don't have to twist my arm too  

hard. But like prion diseases or fungal diseases  where we don't have nearly the same infrastructure  

and level of knowledge, biomedical research  as we do for bacterial and viral diseases,  

if we create the incentive, evolution is  gonna find some weird ways to exploit it.  

It's not just transmissibility and virulence.  Those are like two really basic parameters. 

When you look at even COVID-19, part of what  made it insidious is it just has just the  

right parameters to be latent for just long  enough. The first COVID, SARS-CoV-1, 2003,  

slightly more virulent, and in fact, it was just  more virulent enough that it made you sick pretty  

quick. Just that little difference was enough to  contain it because you could figure out who was  

sick. COVID-19 was impossible to contain because  it took several days before you really presented  

with clinical illness. It's just that little  quirk that made it totally impossible to control  

through non-pharmaceutical interventions early on. Follow that train of thought... if pathogens are  

going to find ways to take advantage, and there  may be pathogens that push the limits on latency,  

it can be very hard to control. One of the  takeaways or the big evolutionary history of  

our pathogens is evolution is very weird, very  contingent, very creative at exploiting whatever  

weakness we give it. It's because there are  billions and billions and billions of microbes in  

this room. I don't know how many tens to hundreds  millions of species of microbes are in this room.  

Most of them are not even remotely pre-evolved to  be pathogenic, but lots are and they're constantly  

seeing if you managed to lock that door.  They're just looking for a way to break in. 

Okay, just a couple more rapid fire questions  for you. Have you found tools like Deep Research  

useful for especially your kind of work where you  just have to compile insights from many different  

fields? If we throw in a question, the kinds  of questions you honestly investigate and now  

maybe they can rely on you as a citation for those  particular questions about what effect did climate  

have on the fate of Rome or something... But if  you just had a different question which maybe you  

would write a book about in the future, how well  do they do at synthesizing this kind of literature  

and coming up with a thesis the way you do? Yeah, amazing. But not yet completely displacing  

or totally threatening the kind of work  that a historian does. But at this point,  

I can't even conceive of what a research  project would look like without using AI. 

Really? Oh, really? That fast it's  become so central to your work? 

Yeah, but for just like, it's just like a constant  conversation partner when you're doing research,  

when you're writing, you know, you can go back  to that PDF and ask whatever, "How many species  

are there in this taxon," or you can just ask the  AI. You still have to check it, but it's getting  

obviously more and more reliable really quickly. But I think it hasn't yet... in some of the deeper  

research, it's not the equal of humans yet,  and then in the synthesis, it's really not.  

There's still that creative element of synthesis  that's... where conceiving of the question is as  

important as the answer. It doesn't feel like  it's right around the corner. But it's changed. 

Have you used Deep Research? Oh, yeah. I started using it  

like two weeks ago or so. I don't know how long  it's been around? Somebody told me about it. 

It's not that much longer. Okay, somebody told me about  

it less than two weeks ago. Yeah, it's  incredible. I mean, it's really incredible. 

Yeah. Now, I want to touch on your next book  that isn't out yet, The Last Animal. One question  

I have is basically how worried should we be  about extinction given that we're on the cusp of  

technologies which will make it possible for us to  reanimate many lost species? I assume if we have  

their genome or something, our descendants will be  able to make more wooly mammoths and saber-toothed  

tigers and so forth. Should we discount the  value of endangered species as a result? 

I would say no. We should still be concerned  with extinction for a couple reasons. One is,  

absolutely this is a legitimate, serious  scientific field to understand the genomics  

of extinct animals. There is small but  serious enough science of de-extinction.  

It's feasible that some organisms could be  targeted for serious de-extinction efforts. 

At the same time, a couple of thoughts. One  is, I'm not that optimistic that it will work,  

not because I think it's necessarily impossible,  although it's not yet totally feasible,  

particularly for animals that don't have very  similar modern descendants. It's because a species  

isn't just a genome. A species is an organism  that inhabits a food web and an ecosystem.  

We could bring the wooly mammoth back, but  there's nowhere for them to live. The mammoth  

steppe that they need to thrive is not there. There's really very little point in bringing an  

animal back from extinction just to put it in a  box at a zoo to satiate our curiosity about it.  

Without the ecosystem, you can't have the species.  One of the themes that I try and get at in the  

book that I'm trying to finish is, we need to  think about living systems, ecosystems, and the  

extinction question is very much a question  of what kinds of systems will exist on the  

planet? Whatever happens technologically in 100  years, 1,000 years, the impacts that humans have  

on biodiversity is gonna be very long-lasting. We're part of a species that has been impacting  

biodiversity for over 10,000 years, and there are  things we can't undo. There are things we can't  

change about the past. We're making decisions  right now that will be binding on the future  

whether our descendants like it or not. We need  to think very hard about what choices do we want  

to make to keep intact the kind of variety and  vibrancy of living systems that in 1,000 years,  

10,000 years, that will be a huge part  of our legacy. The impact that we make  

on the stream of macroevolution will be one of  the really big things that our species does.  

It can sometimes be very hard to recognize  that in our individual lives, but collectively,  

it will absolutely be part of our forever  legacy on Earth. We need to think very  

carefully about the choices that we make. I think that's an excellent note to close  

on. Just to plug one more time, we've  been discussing Plagues Upon the Earth,  

which is the history of disease going back through  the Neolithic to modern times, Fate of Rome which  

discusses the plagues and history of the Roman  Empire considering climate and biology. We also  

discussed, what was the name of the book on  slavery? Slavery in the Late Roman World? 

Slavery in the Late Roman World. Yep. And the upcoming book is The Last Animal. 

The Last Animal. All linked in the description  

below. And where else can people find you? In your descriptions. That's it.  

I’m not on social media, sorry. Okay, got it. Well, you can find  

him here on this podcast. Yes, exclusively.