Human action is not the only relevant parameter in human history

Wednesday, May 30th, 2018

Human action is not the only relevant parameter in human history, Razib Khan reminds us, as he reviews Kyle Harper’s The Fate of Rome:

The Fate of Rome is fundamentally a work of history, but it also takes ecology and evolution seriously. In fact, it foregrounds them. Kyle Harper makes the argument that the expansionary phase of the Roman Empire was not necessarily coincidental, or at least it was lucky indeed because there was a climatic optimum, similar to the one which preceded the demographic expansion of medieval Europe. In contrast, in the 6th century, the world went through some of the coldest years in the Holocene because of a combination of fluctuations in solar radiation and volcanic explosions. I assume that the likelihood of the latter is Poisson distributed, so the combination of decreased radiation and several successive volcanic events can be chalked up to randomness. But its consequences were not random at all.

The climatic changes can have demographic and social consequences obviously. Desperate armed pastoralists can overwhelm states, and change the course of history, just as peasants can rebel from taxes and subordination. And, pastoralists can also bring Yerisina pestis, the plague. Climate is an abiotic pressure which is to some extent an exogeneous shock which occurs randomly, and does not react to human feedback. [This is not totally true, but over the time-scales we’re talking about probably mostly true.] Disease though is a biotic pressure, and though it may relate to abiotic forces, human interaction and agency matter quite a bit.

The Fate of Rome clearly hinges on abiotic factors as initial drivers: a good harvest is good for the state. But the biotic factors, disease, are partly under the control of the state. The Romans did not have germ theory, and were under constant stress due to the high pathogen load, especially of the cities. Harper presents the evidence of high mortality within Roman society well. Because of the endemic ubiquity of disease even elites were impacted by it. But Rome was not just affected by endemic ailments, it was subject to pandemics and plagues.


One of the major insights that Kyle Harper reiterates is that these plagues, these pandemics, are a feature/bug of the Roman imperial system. They are not just the consequence of simply settled agricultural society. As described in books such as Pandora’s Seed, agriculture and settled society transformed the lifestyles of human groups, and many diseases which were rare in hunter-gatherer populations probably became common among farmers. But The Fate of Rome the author argues that pandemics were a novel outcome of complex imperial state-systems with long-distance trade-networks. Small-scale pre-state Neolithic chiefdoms did not have the scale and interconnections to foster plague.

Mass pandemics of smallpox, plague, and influenza are then aspects of civilized life, not, settled agricultural life. This puts the argument of Charles C. Mann in 1493 into greater focus. It wasn’t just more extensive and intensive agriculture in the Old World which left Amerindians vulnerable, it was also that the Old World had thrown up several massive imperial systems which had incubated pandemic producing pathogens (smallpox and influenza epidemics were a major issue in New World societies). These were unleashed at once upon New World societies.

It also suggests to us why adaptation seems to be occurring in the last few thousand years. Bouts of plague which persisted for generations may have driven immunological responses.

Kyle Harper also seems to agree with the general thesis in The Fall of Rome that this period in European civilization was in some ways proto-modern, with economic specialization resulting in a modicum of affluence in ways unimaginable in times before, or after. Trade and some level of mass production allowed British peasants to eat off tableware that was standardized, and not homemade. In contrast after Britain’s post-Roman regression a more local economy had to step in. The most curious fact from The Fall of Rome is that pollution in British ponds did not attain Roman levels until the early modern period, with the rise of industrialization. Again and again The Fate of Rome emphasizes that social and economic complexity achieved in the Roman Empire was not attained in Europe again to the same scale as the early modern period.

Roman wealth was fundamentally due to the returns on scale and specialization that are the hallmark of Smithian growth. Though the Romans did invent a few things, Roman prosperity was not fundamentally driven by innovation. Rather, the Roman peace was a framework for trade and exchange that took advantage of abiotic clement conditions (the Roman climatic optimum highlighted in The Fate of Rome).

But this political system had biotic costs, as well as being subject to biotic shocks. Though Romans may have been wealthier than their Iron Age predecessors in things, and also wealthier than their early medieval successors, they were also a smaller people. Using isotope data Harper suggests that this is not due to Malthusian immiseration as the imperial population pushed up against food supply. Apparently Romans did not subsist on gruel alone, but ate a fair amount of meat, especially pork. Rather it was the high pathogen load enabled by the advancement of Roman urban life and its scale. Rome was a world of intense morbidity.


  1. Bob Sykes says:

    The French Revolution was driven by crop failures in the Little Ice Age. It is probable it drove the American Revolution, too.

  2. Barnabas says:

    Anyone read this book and also familiar with Joseph Tainter’s work on collapse of complex societies and Rome in particular? Which is more on point? For instance, Tainter notes that only the most fertile farmland was worth cultivating in the face of high taxes imposed in the late Roman Empire. Farmers abandoned less fertile land rather than paying the taxes on it exacerbating food shortages.

  3. Kirk says:

    That is going to make for some fascinating reading. I didn’t realize there was this much new scholarship coming out about the Fall of Rome, and it’s clear that there’s been more research done to support many of the arguments I’ve read and agreed with, over the years.

    I’m not so sure that Rome’s fall was really that harmful, over the long haul. Considering all the varied and many vices of Rome, not the least of which was their vicious destruction of neighboring cultures and civilizations (Trajan, I’m looking at you…) to loot them to the ground and enrich Rome, I’m really grateful we don’t have their national behavior surviving into the modern era. You contemplate a lot of what Rome actually was, in terms of culture? You’re going to be forced into a position of “Thank God they’re gone…”. The entire proposition of slavery, as they practiced it? The sexual values and mores that they saw as normal? The public violence of the gladiatorial games?

    No, if you had a modern Rome as your neighbor, I’m pretty sure you wouldn’t be living in a happy nation. It wouldn’t be too far off from having a modern version of the Barbary States still in existence and raiding the coastlines of Europe for slaves and loot.

  4. Lu An Li says:

    The 535 A.D. event. According to Procopius the sun cast no shadow for three years. When it rained it rained yellow rain. When it snowed it snowed yellow snow. Constantinople had it rough but did survive much better than Rome did.

  5. Phil B says:

    There is also the problem of large influxes of peoples into Rome itself. Bringing African, British, German and Middle eastern slaves and traders into Rome also introduced the diseases and parasites endemic to the part of the world. The Roman population and the introduced incomers no doubt “traded” diseases and if they had not built an immunity to those diseases, then a double (or triple) infection would undoubtedly prove fatal before their immune systems could cope.

  6. Kirk says:

    There are probably parallels with the Columbian Exchange, as well: New World immune systems were tuned to deal better with endemic parasites than they were with disease. The Europeans showed up, with all the diseases of “civilization”, and bang, zoom… There goes the native population.

    You might make a point that the difference between the Norse attempts at North American colonization had rather more to do with the fact that they had arguably better hygiene, and no effective sets of civilizational plagues to bring with them, while the somewhat later to the table Portuguese, Dutch, and English brought with them the apocalypse in the form of diseases they’d long since grown immune to.

    So… Did the Romans actually set the stage for the depopulation of the Americas? Did they go through a similar process, due to the communications they created within the Empire?

    One does wonder what the results would have been, were they to have discovered the germ theory of disease earlier on. Imagine the Islamic conquests encountering an Eastern Roman Empire that wasn’t debilitated by the various plagues… Would Islam even exist, today?

  7. Lucklucky says:

    It is more difficult to have plagues in cold climate than in warm climate.

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