惊人的死亡比例

It looks like this particular agent has been killing people for 5,000 years, four or 5,000 years in Western Eurasia and in fact is killing a scarily large fraction of the population. As a quantitative person reading this literature, I think people are embarrassed by the implication.

历史的沉默

The implication is that a third, a quarter, or even half of deaths in this entire period are from this single agent. It's so unbelievable and ridiculous that such a high proportion of people over such a long period of time are dying from it, that people don't even mention it. They just publish paper after paper, focusing on more sequences, without considering the implications of such a high death rate.

古代DNA的发现

When the first large number of DNA sequences from people who lived 5,000, 6,000, and 4,000 years ago from the steppe north of the Black and Caspian seas and in Europe were published around 2015, a group in Denmark led by SK Wellers and Christian Christensen and colleagues looked at their DNA. They discovered pathogen DNA within their sequenced samples. In 5 to 10% of the random people sequenced from around 4,000 or 5,000 years ago, they found Yersinia pestis (鼠疫耶尔森氏菌: 导致黑死病的细菌), the agent of the Black Death (黑死病: 历史上最致命的瘟疫之一).

传播方式与真实死亡率

Interestingly, this ancient strain lacked the plasmid that contributes to bubonic plague (腺鼠疫: 鼠疫的一种形式，通过跳蚤和老鼠传播), which is required for flea-rat transmission. This suggests it must have been transmitted differently, perhaps via pneumonic plague (肺鼠疫: 鼠疫的一种形式，通过空气传播) or something similar. The finding that 5 to 10% of random individuals carried the pathogen implies that the actual percentage of people dying from it was even higher, as not everything present would have been detected. This leads to the implication that this single detectable agent was killing a very large fraction of people in Western Eurasia over this period.

社会动荡与历史类比

What are the implications of this? It might have originated from steppe rodents and spread to farming Europe around 5,000 years ago. This could have resulted in widespread societal disorganization due to the high death rate, creating a situation analogous to what Europeans encountered in the Americas, where societies were disrupted. For comparison, COVID-19 killed about 0.5% of the world population and was highly disruptive. If Yersinia pestis was killing a third or half of the population, its disruptive potential would have been immense, potentially tearing into societal structures, causing civil wars (like potentially among the Inca when encountered by Europeans), and disrupting cultures.

迁徙与人口替代的契机

This disruption in the old ways of life, possibly combined with other factors, could have created opportunities for people from elsewhere to move in, even if they were less densely spread. This sets the stage for understanding a major demographic shift observed in Europe.

欧洲祖源的剧变

A major observation, which the ancient DNA community has been investigating, is that about 5,000 to 4,500 years ago, Europe experienced a radical transformation in the ancestry of its inhabitants. This is a significant event that has been progressively understood through ongoing research.

不列颠的案例与全欧现象

An example is Britain. Around 4,500 years ago, the farming population that had arrived 6,000 years prior, and who built Stonehenge (with the last big stones erected 4,500 years ago), largely disappeared within a century. Approximately 90% of them were gone and replaced by migrants from the continent, bearing ancestry predominantly from the steppe north of the Black and Caspian seas. This pattern is not isolated; it is observed all over Europe, including Spain, Portugal, the Netherlands, Germany, Czechia, Italy, and Switzerland. A wave of people from the east arrived, displacing the established, successful, and densely packed farmers with newcomers who had steppe ancestry and were perhaps less focused on agriculture.

斯堪的纳维亚的墓葬证据

A recent paper from Scandinavia, looking at tombs from about 5,000 years ago, provides further evidence. These tombs belonged to farmers who were on the verge of encountering people from the steppe. A huge fraction of these individuals had Black Death when they died, with infection rates in some tombs even higher than the 5-10% previously observed.

鼠疫的深远影响

This pattern, observed across multiple generations, indicates a substantial burden of Yersinia infection. It's remarkable that this single bacterium is responsible for such devastating historical events. We learn in school that it caused the Black Death, killing a third of Europeans.

工业革命与经济效应

There are even theories suggesting that Yersinia pestis contributed to the Industrial Revolution. The argument is that the plague drove up wages in Britain. With higher wages, there was an economic incentive to develop machines. Economist Robert Allen has proposed this theory, suggesting the plague potentially caused the Industrial Revolution. Furthermore, the medieval plague created significant inflation. Serfs, often on fixed wages, had to be paid more, effectively inflating away their feudal obligations.

青铜时代的人口更替

Another significant impact occurred during the Bronze Age (青铜时代: 人类历史上的一个时期). The plague allowed people from the steppe to essentially replace the existing hunter-gatherer or farming populations across Europe. This facilitated the migration and dominance of people from the eastern steppes over the indigenous populations.

查士丁尼瘟疫与罗马帝国

Kyle Harper's book discusses these events, including the Plague of Justinian (查士丁尼瘟疫: 首次有记载的鼠疫大流行), which is documented as being caused by Yersinia pestis. This plague is believed to have contributed to the fall of the Roman Empire. The impact was profound, leading to population replacement in Europe and, in the second instance, paving the way for what followed, including the advent of modernity.

历史的单一病原体

It's astonishing that one disease, and Yersinia pestis in particular, has played such a significant role in human history. Its impact may have even extended to the New World, although its role there as the primary pathogen is less clear. The fact that not only disease, but this one specific bacterium, has had such a profound influence is truly remarkable.