Population collapse and chance

by Edward Pegler on 14 July, 2018

What do Alexander the Great’s march on Asia, the Arab Conquests and overly hard exams have in common? The answer is the increased chance of getting lucky when the numbers are low.

So you’re sitting in an exam and the questions seem exceptionally hard compared to all those practice papers you were doing. How should you feel? Frustrated? Fair enough. After all this seems unfair. Comforted? Up to a point. If the paper is generally hard then the exam board is going to have to scale up everybody’s mark. Uncertain? Well, yes. Because you could get a worse mark than you really deserved…

… but on the other hand you might just get lucky.

Low numbers and luck

Why? Let’s take an extreme case. The exam has 100 marks in it. In a perfect world people doing the exam could get 101 different marks (0 to 100). If you divide that into five categories (crap, poor, average, good and great), that’s about 20 marks for each category. If you were lucky and scored 4 extra marks for getting one rather complex question right, due to having a dad who knew about such things, you could be called good instead of just average. So what?

But what if the exam was so hard that the best mark in the exam was only 9, people having scored 10 different marks (0 to 9)? Now the exam board has to use this range for its categories, which means that there’s only 2 marks for each category. In this case, if you managed to get lucky and score 4 extra marks on some complex question, due to having a dad who knew about such things, you could be called great instead of just average.

(Of course it could go the other way. And remember that the same rules apply to everybody. Indeed this effectively means that such an exam is invalidated as a way of checking people’s ability.)

So what’s this got to do with ancient history, or even prehistory?

Great Men, Great Machines, Great Philosophies?

The reason is simple. People often look for a genius or a fundamental religious or technological cause for some astonishing event which changes the future. We all know of Alexander the Great’s extraordinary military prowess or of the religious zeal of the Arabs in the 7th century. We think that we are equally aware of the astonishing power of horse riding or of the lethal effects of the arquebus.

But are people really so infallible? And in what way is this religion so much more oomphy than that one? And surely some of the locals might take to using horses or those guns on the attackers. In fact, in the short term people do often achieve advances through military genius, technology or whatever, but the long term effects are rarely, if ever, that great.


There is one notable exception to this, introduced to most of us by William McNeill in his memorable book ‘Plagues and Peoples’. He certainly wasn’t the first to say it, but the idea that the Americas were won for the Conquistadores and other European settlers due to wiping out natives by European disease has taken a powerful hold on our imagination. No technology, religion or genius is now invoked in this conquest.

Such causes may well also explain the Bronze Age expansions of peoples from the steppe, as argued tentatively by David Reich. However, I don’t think that people would argue for the introduction of disease to the Mediterranean and Middle East by the Arabs, or to central Asia by Alexander’s army (many of whom probably came from central Asia).

Low populations and luck

However, these radical moments in history become much easier to explain when the population of a region shrinks to a half or less of its original size, due to some general epidemic which affects everyone. For in these situations chance can become much more significant.

A clear example of this seems to be the widespread epidemic known as the Justinian Plague, which started in the mid sixth century and continued to reduce the population of the Mediterranean and neighbouring regions for the following 150 years. Events which followed this include the great Slavic Migrations and the Arab Conquest. These were world-changing.

However, a similar case can also be made for an earlier epidemic in the Mediterranean a thousand years before this, around the second half of the fifth century BC. Records of it are scarce, consisting only of Thucydides detailed account for Athens and a brief mention by Roman chroniclers. However, it’s extent may have been much greater than is generally realised. Its possible consequences were the near annihilation of Rome by the Gauls (bad luck) and the subsequent rapid rise of Rome in the Samnite Wars (good luck), as well as Alexander’s great Eastern campaign, events which happened in the hundred or so years of population fall after the first outbreaks of epidemic.


History is not predestined. It’s not a predictable science like big-scale physics. Humans do change and that changes the way that they behave in comparable situations. However, I do believe that statistical patterns can be discerned and those have much to do with chance.

Personally, I have little doubt that depopulation periods of various magnitudes have happened throughout the last few thousand years but that little or no account of most of them survives. Such periods, if they exist, will, in my opinion, correlate with significant historical events. In the west we tend to play down the significance of such depopulation periods. The last one that happened, following The Great Pestilence or Black Death, which took place from the mid fourteenth to the sixteenth centuries AD, didn’t really correlate with any significant changes from a western point of view (well, maybe the rise of slavery). However, from the point of view of Eastern Europe and Asia the effects were much greater, with Turkish expansion, the collapse of the Tatars and the second serfdom.

My guesses at ancient depopulation periods in western Asia, including Europe, are 3000-2800 BC, ??2100-1900 BC, 1750-1550BC, 1350-1100 BC and 800-1000 AD. However, apart from some textual evidence for ancient epidemics (for the eighteenth and fourteenth centuries BC), they are largely based on hunches. Trying to find a good way to spot depopulation will be the job of radiocarbon specialists like Ian Shennan and geneticists like David Reich. Seeing if depopulation correlates with major events will be the job of archaeologists and geneticists. But for the first time such a thing seems possible.






Indo-Iranian language from the steppe it seems

by Edward Pegler on 1 April, 2018

Backing the wrong (or no) horse again!

Just for anyone who hasn’t found it, there’s a preprint of a paper called, rather uglily, ‘The Genomic Formation of South and Central Asia’ on bioarxv. It’s all about the ancient DNA of Central Asia, Iran and northern Pakistan from the Bronze Age to the Iron Age.

This is a quick comment just to say it seems to suggest that Indo-European languages, probably in the form of Indo-Iranian, were introduced to India from the steppe via the Altai Mountains and Hindu-Kush around 1500 BC (Middle to Late Bronze Age). This is what most people have thought for a long time. Well, most people but me. Once one concede’s that Indo-Iranian languages come from the steppe, then Greek and Armenian coming from the steppe is highly likely. Why not throw in Anatolian while you’re there.

The only thing I find a shame is that this new paper from the Reich team is not as unequivocal as it should be. I’m guessing that Indian academics were not willing to release data from India at this stage, or that no ancient DNA was forthcoming from Indian (or even southern Pakistan) samples. What’s missing, more than this, from the paper, is data from Pakistan before the arrival of people from the steppe. Sadly, this makes it still possible for someone more stubborn than me to hold out hope for Indo-European associated with Harappa, etc, but I think that’s probably desperate.

At least it means that I can return to what I started this blog on, which was ancient economics. What a relief all round.

Addendum – not criticizing content but this paper looks rushed. I’m sure it’s going to get cleaned up before publication (Nature?) but it needs an interpreter to read the diagrams at the moment.


Narasimhan, V. M. et al. (bioarxv preprint March 2018) The Genomic Formation of South and Central Asia.


The causes of language swapping and language shift

March 5, 2018

A review post outlining three main methods of language swapping: 1) Biggest language wins, 2) Richest or most violent language wins (this is helped if languages are similar), and 3) Everyone’s second language wins. This post is aimed at anyone who’s interested, although it comes from a particular discussion between me and others about the […]

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Words and rules, and the contrasting family trees of Indo-European

January 30, 2018

So, do the different linguistic family trees of Indo-European tell you different things? I think that grammar-based trees are better at telling you about the original splits between language sub-groups, whereas word-based trees can tell you about how isolated those sub-groups became. At the beginning of the millennium two papers were produced which both purported […]

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Proto-Indo-European homelands – ancient genetic clues at last?

November 12, 2017

(Neditors note – You know I now realise that so much of the argument below depends on my belief that elite dominance is not a sufficient mechanism for language change. I prefer to see major intrusion of a new language carrying people as necessary (i.e. that 30% or more of the population will now be […]

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No South American DNA in ancient Easter Island – and…?

November 4, 2017

Regardless of whether Rapanui ever made contact with South America, is the lack of ancient DNA evidence of South American contact in Easter Island that surprising? A very recent paper by Lars Fehren-Schmitz, Pontus Skoglund, and others, based on the ancient DNA (mitochondrial and nuclear) of five Easter Island / Rapanui individuals dated before 1700 […]

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European ancient DNA – the movie

October 1, 2017

We have learned loads from the autosomal DNA analyses of Europe’s ancient populations which have poured out of Harvard and other universities in the last two years. Europe was a restless place, changing people more than some of us would have guessed. Here’s the movie adaptation. I put together the video above for my own […]

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What type of grass are you on, Jared?

July 5, 2017

Does agriculture start with lucky grass, as Jared Diamond says, or does lucky grass start with agriculture. I’ve been sitting enjoying the weather in my garden in Swindon, England. It’s a mess, full of random weeds and overgrown grass. But who cares? The Sun’s out. And there is a particularly fine, architectural grass growing just […]

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Violence in the Near East at the dawn of agriculture: conflict vs co-operation

December 22, 2016

Small population size and little need for competition is an excellent explanation for the lack of conflict during the transition to agriculture. However, there’s also another possible explanation – co-operation. In my previous post I tried to gather together the evidence for violence in the transition from foraging to farming across the Near East. Much […]

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Violence in the Near East at the dawn of agriculture: the evidence

December 10, 2016

Does farming lead to violence, violence lead to farming, or was the period during and after the invention of farming in the Near East as peaceful as it gets? You’ll find many opinions on the role of farming on the origins of violence and of violence on the origins of farming in human history. I’m […]

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