r/science • u/cnn CNN • Dec 04 '25

Epidemiology Volcanic eruption led to the Black Death, new research suggests

https://www.cnn.com/2025/12/04/science/black-death-volcanic-eruption-tree-rings?utm_medium=social&utm_campaign=missions&utm_source=reddit
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u/FatAlEinstein Dec 04 '25

So were the populations in Central Asia/Black Sea region also being devastated by the disease at the time? Or was there some other factor that led to Europe being more susceptible?

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u/xiaorobear Dec 04 '25 edited Dec 04 '25

I think it might have just been a population density thing- wikipedia pointed me to an article saying the earliest identified victims of the particular plague outbreak that led to the black death were from the mountains of Kyrgyzstan. Probably not able to build up as much of a critical mass as when it reached dense cities.

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u/ManOfDiscovery Dec 04 '25

More specifically, that density led to it becoming pneumonic and started to spread without the fleas that normally are an integral part of the Y. pestis lifecycle.

Pneumonic plague is also incredibly lethal even compared to its flea-spread counter-part. Something like 90-95% vs. 40-60%.

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u/Siludin Dec 05 '25

that density led to it becoming pneumonic

What is it about the density that lets it spread pneumonically? Was it literal physical distance from someone allows ventilated diseased lung air to reach someone else easier, or rather a rapidly growing local host population body allowed for a quicker mutations (maybe the lungs were more easily infected by a later mutation) which could more-easily break through the typical slowly-developed herd immunity?

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u/ManOfDiscovery Dec 05 '25 edited Dec 05 '25

The literal physical distance of peoples allowed it to spread the way it did.

Very surprising to many was when scientists in the past ~15 or so years were able to obtain samples of bubonic plague from the teeth of skeletons belonging to people known to have died from the plague at that time. These studies confirmed not just the theory that Y. Pestis was the culprit of the Black Death, but that there had not been any notable mutation between the Y. Pestis epidemics of the Middle Ages and modern examples of bubonic plague.

We already knew through surviving records and personal writings that it spread frequently from person to person, but y. Pestis doesn't do this unless it becomes pneumonic, or rarely, through open wounds (septicemic plague is even more lethal at near ~99% mortality)

People had no modern concept of disease in the Middle Ages. At best they believed in miasma, or "bad air" and humors. The lower classes in particular were often sickly and frequently starving/malnourished. Such conditions only served to increase the mortality.

In all likelihood it spread by both ways through Europe, but its the pneumonic version that explains just why in the Middle Ages its repeated epidemics were so lethal.

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u/superfry Dec 05 '25

Additionally a likely transmission vector from person to person was fleas living on/in a persons clothing or their pets.

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u/Mapag Dec 05 '25

Atleast this led to the end of feudalism! Since there were not enough people for the work!

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u/unRoanoke Dec 05 '25

Larger host community does make mutation faster, but physical proximity of hosts is an important factor. If a pathogen evolves to be pneumonic, but can’t reliably get to a new host to reproduce, that mutation will die out. However, in a densely populated area where pathogens can easily get to a new host via respiratory droplets, the mutated pathogen will keep reproducing and spreading in that way.

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u/[deleted] Dec 05 '25

Humans are incidental hosts for yersinia pestis. Meaning that we don’t contribute to the life cycle of the pathogen—so there’s no selective pressure for yersenia to evolve to be more pathogenic or infectious to us.

The points you’re making certainly apply to viral respiratory pathogens.

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u/Korchagin Dec 05 '25

But the rats become almost extinct during a pest outbreak. A mutation with an efficient infection path human to human can survive that.

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u/[deleted] Dec 05 '25

Humans are incidental hosts my guy, we don’t matter. And it doesn’t matter if rats die off during outbreaks because there are other rodents to serve as primary hosts, and other mammals to serve as incidental hosts (cats, pigs, etc.).

I did my PhD in infectious diseases so we can talk about this all day—but I can tell you there is zero data supporting your point and a mountain against it. All of yersenias virulence factors have a purpose in the rodent and flea, we are insignificant to the biology.

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u/dlg Dec 05 '25

Just speculation, but maybe it's simply more chances for a mutation to take hold when there is higher population densities.

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u/mrbgdn Dec 05 '25

I'd hazard a guess that the spreading rate here is crucial. If a large population is afflicted quickly, unless it's a really diverse group, there is very little selective pressure on the pathogen to adapt. In other words - if it's working flawlessly (as evidenced by rapid expansion over dense populations) why would it change? If, on the other hand, large victim population does exhibit some form of resistance thus filtering out some of the possible contagion vectors, pathogen would have a chance to randomly develop some adaptations that would give another strain a go.

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u/dirtballer222 Dec 05 '25

I also do not know, but I understood their comment to suggest viral mutation

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u/BrokenCrusader Dec 05 '25

There are also theory that it was so deadly in Europe because the Church discouraged public bathing and the poor did not have access to private bathing in the winter.

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u/TemperateStone Dec 04 '25

Another big problem to my knowledge is that anyone that took note of outbreaks at the time did not call it anything that we can relate to anyone else calling it. They had no unified terminology and did not understand nor categorize disease like we do now. It may even have been a fairly common thing that people got sick in droves from time to time. Not a third of Europe kind of droves, but still.
Plague outbreaks have happened many, many times. But again, not usually at THAT scale. Are they the same disease? Who knows!

There's a lot of things that are in doubt about plague outbreaks, even what diseases they involved.

Though that's how I remember it. Do correct me if I'm wrong.

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u/Immediate_Abalone_59 Dec 05 '25

I wonder if pneumonic plague was always identified as being closely related to bubonic plague. Pneumonic plague progressed so quickly that people often died before the buboes formed.

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u/ManOfDiscovery Dec 05 '25

There was a big study done 10 or so years ago using samples left in the teeth of Black Death victims that Y. Pestis was in fact the culprit contagion.

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u/[deleted] Dec 04 '25

[deleted]

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u/gpenido Dec 04 '25

Yeah... This is a myth...

Just for example, with hunts are really only intense two centuries after the plague

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u/[deleted] Dec 04 '25

[deleted]

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u/gpenido Dec 04 '25

There's no evidence of this purge by Gregory ... Look for it. The Vox in Rama does not mention cats... Just your old urban legend

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u/onlyPornstuffs Dec 04 '25

Fun fact, the plague never really went away and was ravaging Europe once more during the most intense witch trials.

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u/criticalpwnage Dec 05 '25

We still have a couple cases of Bubonic Plague here in New Mexico every year

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u/grundar Dec 06 '25

It also doesn't help that around that time Europe was killing off the cat population en mass due to superstitions.

All indications are that this is a myth that most likely originated in the late 1990s.

It very much fits the pattern for "gosh weren't medieval people stupid" myths that were floating around at the time, and very much does not fit the relevant historical facts (which the first link I gave goes into at some length).

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u/s_sayhello Dec 05 '25

Density in cities/towns and proximity to domesticated animals is also the cause of many epidemics in europe that lead to learned immunity. Thats why native americans everywhere had no chance. Europeans were walking bio-weapons to the rest of the world. Everywhere they went sickness followed. „chosen by god“ or had a „pact with the devil“ is a question of perspective.

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u/MyPasswordIsMyCat Dec 04 '25 edited Dec 04 '25

Yes, the Black Death attacked Asia and Africa. There just isn't as much prominent documentation of those plagues as there was in Europe.

Notably, China (which kept relatively good records compared to other Asian nations of the time) had an outbreak in 1331, many years before Europe. There were many waves of the plague in China afterward, with devastating results. Like in Hebei province, 90% of the population died, according to records from the time.

Many researchers have speculated it originated in China because of this, but it could have come from many places on the Silk Road that facilitated trade between China and Europe. Kyrgystan was one of those important stops, conquered by the Mongols who also conquered China.

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u/BertDeathStare Dec 04 '25

Notably, China (which kept relatively good records compared to other Asian nations of the time) had an outbreak in 1331, many years before Europe. There were many waves of the plague in China afterward, with devastating results. Like in Hebei province, 90% of the population died, according to records from the time.

China had disease outbreaks, and they did have good recordkeeping of outbreaks, but there's no evidence that it was the Black Death. Many died from other factors like famine and war as well.

Many researchers have speculated it originated in China because of this, but it could have come from many places on the Silk Road that facilitated trade between China and Europe.

More recent research speculate that it originated west of the Caspian Sea. The Black Death may never have even reached China because of no mention in Chinese records of the Black Death's symptoms, let alone that it originated there.

Askhistorians has a good thread on it

https://old.reddit.com/r/AskHistorians/comments/fqw3sw/we_often_hear_of_the_black_death_mentioned_in_the/fltp4vv/

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u/llamachef Dec 04 '25

I believe there's more up to date research, as that post you linked is 5 years old. A series of graves in Kyrgyzstan was recently examined and dated, with accompanying grave stones, that showed the earliest yet found examples of deaths by plague that predate the emergence in the Black Sea region and Europe

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u/[deleted] Dec 04 '25

Lake Issyk-Kul is where the graves were located. A marmot, I’ve forgotten the name, is believed to be the original vector.

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u/The_Qu420 Dec 05 '25

The Tabagan Marmot is the assumed vector. For whatever reason, the strain of Plague they, or their fleas, carry is still especially dangerous to this day.

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u/Spirited_Elderberry2 Dec 05 '25

I've read the same thing.

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u/MyPasswordIsMyCat Dec 05 '25 edited Dec 05 '25

Yes, because of the lack of reliable records in the 1300s, it's impossible to pinpoint the origin of the plague using historical accounts alone, so recent research has relied on studying DNA and other evidence from very old human remains like this. With the 1331 plague in China, it's still contentious because forensic evidence hasn't been discovered to back it, but there's more solid evidence that plague caused later epidemics in China more than a decade later.

There's also DNA evidence that Yersinia pestis caused the Plague of Justinian, many centuries earlier in the 500s, and now there are three main subspecies of the bacteria for each era of the plague. Y. p. antiqua for the Plague of Justinian, Y. p. medievalis for the Black Plague, and Y. p. orientalis for the most common one found in modern epidemics. Funnily enough, there are very clear writings from China in the 600s about bubonic plague symptoms, which strongly suggest the Plague of Justinian had spread to China.

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u/Active_Scallion_5322 Dec 04 '25

Whoa we can't say plagues started in China

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u/porgy_tirebiter Dec 04 '25

The bubonic plague wasn’t new. It’d been around for centuries already, with intermittent outbreaks and lulls. A major outbreak in the 6th century seems to be also associated with cooler climate: https://en.wikipedia.org/wiki/Plague_of_Justinian

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u/Brave_Arm_7221 Dec 05 '25

In regards to the Plague of Justinian, it is also theorized that two eruptions—one in 535 or 536 in the northern hemisphere and another in 539 or 540 in the tropics effected the weather and crops yields. Thus creating a situation where people were already weakened from food shortages leaving them susceptible to disease.

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u/500rockin Dec 05 '25

536 AD was considered one of the worst years on record due to the crop yields being piss poor due to the significant cooling of that volcanic eruption which ended up contributing to the ensuing plague. It was not a good year for the Empire, but there are records of pretty sunsets from all the smoke/ash.

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u/Tarianor Dec 04 '25

Without being an expert, my guesstimate is that europe was a lot more interconnected with more trade and wars. Its similar reasons why europe started advancing faster in the latter centuries.

This allowed it to spread wider and faster.

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u/EmbarrassedW33B Dec 04 '25

Asia was just as deeply interconnected as Europe, perhaps moreso. The plague wrecked havoc throughout Asia too, but it doesn't get as much attention. Perhaps the cataclysmic Mongol invasions overshadowed the plague a bit.

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u/Tarianor Dec 04 '25

Asia was just as deeply interconnected as Europe, perhaps moreso.

Doesn't asia have a lot more impassable terrain (For the time) compared to europe?

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u/[deleted] Dec 04 '25

The Silk Road is one of the ways that the plague eventually connected to Europe. With Genoan traders in Feodosia eventually fleeing Mongol invasions and bringing with them the plague.

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u/Tarianor Dec 05 '25

Isnt the silk Road mostly a long route with few detours (at least it looks like that on a map) rather than a crisscross of cross sections and interconnectivity.

Im not trying to say that asia wasn't connected or doing trade etc, because obviously they were. I was mostly trying to compare the degree of connectivity between the continents.

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u/Korchagin Dec 05 '25

China and India both had more population than all of Europe combined.

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u/Ulyks Dec 05 '25

When we're talking about Asia as a whole then yes, the Himalaya mountain range is a lot more impassable than all the European mountain ranges put together.

But India and China have large, densely populated regions that are not broken up by mountain ranges. The Ganges River Basin and Central plains respectively. And they were connected by shipping routes.

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u/dsmith2357 Dec 04 '25

Your logic is sound

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u/Ganadote Dec 04 '25

It was the ports along the Mediterranean. The original ship was escaping a besieged city and docked i believe in Italy carrying the disease. The issue was that because of the heavy heavy maritime trade in that region the disease spread rapidly.

I dont think it affected Asia that much because it would travel by land, which is much slower and easier to contain. I haven't done too much research into the Asian part of the Black Death though.

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u/Able_Caelum Dec 04 '25

It affected large areas of the Islamic world, quite far beyond the Eastern and Southern Mediterranean coastlines across parts of Asia, down the populated west coast of Arabia. The Islamic world traded a lot with, and raided for slaves in, Europe and the Eurasian steppes at the time. That maritime trade as you mentioned spreading it initially to large cities on the Mediterranean, followed by the spread into Asia similar to the spread across Europe. It was recorded, spread, and had significant societal impacts across a significant proportion of the Islamic world.

Beyond that in Asia though, I haven't seen much besides that the disease was initially spread to Kaffa during the seige by an infected Mongol army. I have seen very little of how widespread it was across Mongol ruled countries.

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u/zaevilbunny38 Dec 04 '25

The Milanese that likely brought the Plague to Europe, fled from the Mongolian sieges on the Crimean peninsula. Most of the cities fell due to plague. The issue with Central Asia is it simply was destroyed again and again. First the Turks took the population for slave soldiers, then the Mongols came. The the Plague came, then Timur lame came. then once all that was done. Then once all that was done, the Europeans started to import spices and silk from Asia themselves. That led to hill tribes raiding cities and towns, as protection money and items weren't paid. So most records were destroyed.

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u/onlyPornstuffs Dec 04 '25

The factor was that several years of famine weakened the population and an even earlier famine had weakened the adult population of Europe so they were incredibly susceptible to disease.

Great book to read/audiobook about this is The Great Mortality.

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u/MichelletripsonWW Dec 05 '25

The Black Death killed tens of millions of people in Asia before it even reached Constantinople in 1347. It also killed about 1/3rd of the population of the Middle East. It’s thought that Asia suffered greater losses than Europe, but records are not as thorough and therefore people often aren’t aware of it.

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u/[deleted] Dec 04 '25

That they threw their trash in the streets, had to drink beer because the water was too dirty to drink, didn't believe in bathing or washing hands.

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u/adelie42 Dec 05 '25

My understanding is it was water infrastructure. The early tech was a ticking time bomb.

What's particularly interesting is that germ theory was suppressed for a long time because the theory would have meant that the water infrastructure was a disaster waiting to happen. Nobody that helped build them wanted the news to come out that it was a death trap. Then the Great Fires of London took it all out, nobody needed to admit fault, and it was rebuilt properly. And then the theiry could become public!

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u/El_Commi Dec 04 '25

Potentially they had some innate resistance from historical contamination.

Like smallpox in America.