Kyle Harper

And so it has no evolved incentive to modulate its virulence to be able to transmit sustainably.

Plague never sustains itself in human populations.

It can transiently infect human populations, but then it always dies out.

It becomes extinct, that lineage.

Yeah, this is – you need to ask me in five years because we've learned so much and now this is like the thing that we fall in the category of like almost a new question now that we can ask because now that we have the Neolithic –

lineages and the Bronze Age lineages we're starting to like piece together this fuller history but we still don't even like totally understand the boundaries of when is the plague really sort of not circulating in human populations and what are the factors that cause it to be so explosive like is it evolution of the bacterium is there something about the genetics of the lineages that escape from the animal reservoirs that are like especially transmissible is it

Human ecology, like that we put rodents, like black rats, you know, in the right place to get the disease.

Is that there's something about the climate stress that renders the – we don't have a great understanding of like why the plague comes and goes.

So that's scary.

And the –

The – connecting it to the – your other question about like these superbugs.

I mean what's interesting in the very big picture about the plague to me is like – even like the history of infectious disease is like on the one hand, like there's a real core of it that's just like basic principles of ecology and evolution.

I mean we do certain things in the environment that creates the conditions that pathogens can evolve and take advantage of.

But on top of that, like evolution is just creative and weird and contingent and unpredictable.

And it's those little like contingent facts that can end up having these really, really huge effects.

And so in the case of the plague, like you would never –

If you were like really, really knowledgeable about the basics of ecology and evolution of disease, you would never be like I think that, you know, every now and then a rodent disease from Central Asia is going to wipe out half of the continent.

Like that shouldn't – that's not predictable.

That shouldn't be happening.

And actually that one is kind of an outlier.