David Reich

Yeah.

There is a lot of reason to think that some of these events have been recurrent throughout history, and that it's not just difference between farmers and hunter-gatherers, but actually a lot of different types of interactions that are occurring.

So the example that you mentioned is something that's been a big shock from the ancient DNA revolution.

So this is now maybe eight years, nine years old.

So when the first large number of DNA sequences from people who lived five and six and 4,000 years ago in the steppe north of the Black and Caspian Seas and in Europe were being published about in 2015, this group in Denmark

led by S.K.

Willerslev and Christian Christensen and colleagues, looked at their DNA and they discovered in their sequence from the 100 or so humans they sequenced that there was also pathogen DNA.

And in 5% to 10% of the random people they sequenced around 4,000 or 5,000 years ago, there was Yersinia pestis, which is the agent of the Black Death.

But actually, without the

without the plasmid that contributes to bubonic plague that's required for flea rat transmission.

So it must have been, for example, pneumonic plague with the aerosolized transmission or something.

But five to 10% of random deaths means that actually the percent of people who were dying must have been even higher.

higher because they weren't detecting everything that was there.

A study by another group, Johannes Krauss and colleagues, of people in plague pits in London from the 1300s epidemic found that when you apply this method to people we know died of Black Death, you only find a quarter of the people, so the rate was even higher.

If people are bacteremic when they die, if they have bacteria in their teeth, they probably or almost certainly died of that agent.

So a paper just came out a few weeks ago in Scandinavia looking at these tombs from about 5,000 years ago of farmers who were just on the verge of encountering people from the steppe.

And a huge fraction of them have black death when they die.

They're buried in tombs and normal, even higher than 5% or 10%.

So this whole pedigree with many, many generations, so it's not all at the same time.

Just like the parents, generation to generations, a very large fraction, like well more than 10%, have black death and have Yersinia infection.