korrents

korrents · Dwarkesh Podcast

David Reich – Bronze Age shock, the Neanderthal puzzle, & the sudden spread of farming

David Reich · 2h 13m · youtube.com ↗

26 korrents from this recording

1h2h
David Reich did not write this page.

Every claim below is a statement made in this recording, quoted word for word and linked to the second it was said, so you can hear it rather than take our word for it. The wording comes from the transcript published alongside the recording; the sentence above each quote is our reading of the claim, not their wording.

  1. 0:02:12 · watch on youtube.com↗

    Our reading

    Ancient DNA has been a triumph about migration and a failure about biology, and the reason is simply that the samples were too small.

    Their wordsBut, what's not been successful is learning about uh biology and biological change. And one big reason for that has been that the sample sizes have been too small.
    Interesting
  2. 7 min later

  3. 0:08:44 · watch on youtube.com↗

    Our reading

    Adaptation accounts for only about 2% of the change in human gene frequencies; the other 98% is migration, mixture and drift.

    Their wordsUh and 98% of it is other factors, especially genetic drift. So it's overwhelmingly migrations and population structure causing fluctuations in frequency.
    Interesting
  4. 2 min later

  5. 0:10:21 · watch on youtube.com↗

    Our reading

    Periods of migration are the worst moments to look for natural selection, not the best, because they drown the signal in huge frequency swings.

    Their wordsAnd really from a statistical point of view, what happens at these times of migration is there's just huge fluctuations in frequencies, and these are extremely uninformative times for looking and detecting natural selection.
    Interesting
  6. 3 min later

  7. 0:13:03 · watch on youtube.com↗

    Our reading

    Natural selection in humans has not been quiescent: it is tugging almost every position in the genome in one direction or another, everywhere.

    Their wordsIn fact, multiple analyses we do suggest that the genome is vibrating with natural selection, and uh there's all sorts of weaker effects that are there that would be picked up in larger studies even than we've done. Uh and that uh in fact, almost every position in the DNA is uh correlated to a position that in being dragged in one way or the other uh by natural selection. Instead of being quiescent, natural selection is everywhere.
    Interesting
  8. 3 min later

  9. 0:16:12 · watch on youtube.com↗

    Our reading

    The weak selection signal on behavioural traits is a shortage of statistical power, not evidence that behaviour was unselected.

    Their wordsIt may still be the case, and I guess it is, that immune traits are the most selected category, but is not at all the case, and in fact, we can prove it's not the case that behavioral traits are not selected.
    Interesting
  10. 11 min later

  11. 0:27:11 · watch on youtube.com↗

    Our reading

    The Bronze Age, not the invention of farming, was the shock the human genome reacted to most strongly.

    Their wordsour cartoon picture is that the big transition is farming, but the genetic data, the biological readout is saying our genome is reacting much more strongly to this these events that happened 5,000 years ago.
    Interesting
  12. 2 min later

  13. 0:29:03 · watch on youtube.com↗

    Our reading

    Finding no selection in African-Americans over 300 years is not evidence against selection: five generations is simply too short a time to compound.

    Their wordsAnd so one possible explanation for that is just that there's only a handful of generations maybe five over which the natural selection would operate. And so maybe if the selection was 2% a generation you would still only see maybe a 10% compounded effect and there's just not enough time to detect it. But the Bronze Age is not 300 years, it's 3,000 years. It's the power of compound interest and you have enough time to begin to see a strong effect.
    Interesting
  14. 2 min later

  15. 0:31:29 · watch on youtube.com↗

    Our reading

    Selection on the genetic predictors of cognitive performance peaked in the Bronze Age and has left no trace at all in the last 2,000 years.

    Their wordsAnd what you see when you look at intelligence is you see that this maxes out in the Bronze Age between 5,000, 4,000, 3,000, 2,000 years ago. And the impact in the last 2,000 years is almost nothing. There's no evidence of natural selection at all.
    Interesting
  16. 9 min later

  17. 0:40:48 · watch on youtube.com↗

    Our reading

    What has actually been under selection is probably not intelligence but a general trait more like executive function or the propensity to defer gratification.

    Their wordsThere seems to be some kind of general trait that maybe you could think of as executive function or maybe propensity to defer gratification or something or I'm just just waving my hands that is under selection and it pushes all these traits in the same direction one way or the other
    Interesting
  18. 2 min later

  19. 0:42:33 · watch on youtube.com↗

    Our reading

    The selection signal on the genetics of schooling is not a European artefact: the same variants predict years of school in China, a population disconnected from Europe for the whole period.

    Their wordsSo we just could not see a way this could happen by chance and once we saw that we really felt quite convinced that this was a real signal and that really somehow there has been natural selection to increase the genetic changes that today manifest themselves as more years of school at predicting more years of schooling.
    Interesting
  20. 4 min later

  21. 0:46:34 · watch on youtube.com↗

    Our reading

    A society that intensely values intelligence is unprecedented in human history; the Bible, Homer and other ancient texts value strength, courage and beauty instead.

    Their wordsFirst of all, I think we are speaking from the point of view of a society which intensely values this particular trait, you know, ability to score well on IQ tests or things like them or to go to school for a long time or whatever it is. And I think this is unprecedented in human history that we live in a time like this.
    Interesting
  22. 5 min later

  23. 0:51:31 · watch on youtube.com↗

    Our reading

    Complex human traits have not been pushed steadily in one direction because both ends of the spectrum carry advantages in different times and places.

    Their wordsmy sense is that these complex traits have not pushed in one direction because there's advantage there's spectrums where there's advantages to both ends of the spectrum
    Interesting
  24. 2 min later

  25. 0:53:59 · watch on youtube.com↗

    Our reading

    Europeans have been under selection against body fat for 10,000 years because farming made the food supply steadier, not less stable.

    Their wordsAnd so, maybe what you're seeing is that this group of people in Europe and the Middle East over the last 10,000 years has moved into a a period of relatively more stable food, where building up stores of fat are not as advantageous, and there's been selection against this combination of traits.
    Interesting
  26. 2 min later

  27. 0:56:17 · watch on youtube.com↗

    Our reading

    Famine cannot be what selected for fat storage, because a fat store built after a hunt cannot carry anyone to a famine three years later.

    Their wordsYour fat store from, you know, the latest hunt is not going to carry you through to the famine 3 years later. And so survival of famines is a different thing than building up body fat for being able to survive 2 weeks later.
    Interesting
  28. 2 min later

  29. 0:57:48 · watch on youtube.com↗

    Our reading

    There is more room at the top for every human trait: push selection harder in any direction and the mean would move, at some cost elsewhere.

    Their wordsBut I think it's highly likely that if natural selection was pushed pushed any of these traits in more in one direction than it is, the mean would move.
    Interesting
  30. 2 min later

  31. 0:59:24 · watch on youtube.com↗

    Our reading

    For any trait built out of many mutations, all the variation needed to move a population to a new adaptive set point already exists inside it.

    Their wordsSo for complex traits, ones underpinned by many mutations, all the variation already exists to move the population to a different adaptive set point that's optimal in the environment which it's in.
    Interesting
  32. 3 min later

  33. 1:02:51 · watch on youtube.com↗

    Our reading

    Population size is not what limited human adaptation; time is. A selection coefficient of half a percent works as well in a thousand people as in a million.

    Their wordsSo we're talking about strong measurable selection coefficients on the order of half a percent or more in this study and all of those are going to work in small populations or large populations. It's not going to be affected by the population size.
    Interesting
  34. 2 min later

  35. 1:05:14 · watch on youtube.com↗

    Our reading

    There was no genetic switch for behavioural modernity: no selective sweep is shared by everyone alive today in the period the cognitive revolution supposedly happened.

    Their wordsThis is like a crazy result because uh it looks like there's no key selective sweeps that have occurred in this period that is ancestral to everyone living today.
    Interesting
  36. 10 min later

  37. 1:15:26 · watch on youtube.com↗

    Our reading

    Every cognitive ingredient for farming and for states was already in place tens of thousands of years before either appeared, so what humanity was waiting on was not biology.

    Their wordsSo, the cognitive resources for doing this must have all been in place, but it's a very long fuse.
    Interesting
  38. 6 min later

  39. 1:21:49 · watch on youtube.com↗

    Our reading

    In many places in your genome you are more closely related to a Neanderthal on your mother's side than you are to your own father.

    Their wordsSo, there's many places in your DNA where you're more closely related to a Neanderthal on your mother's side than you are to your father.
    Interesting
  40. 3 min later

  41. 1:25:12 · watch on youtube.com↗

    Our reading

    The right way to think about Neanderthals may be as culturally modern humans who ended up mostly archaic genetically.

    Their wordsSo, uh I'm interested in the possibility that actually the right way to think about Neanderthals is actually as somehow culturally modern humans. Uh and uh even though that genetically they're mostly Denisovans.
    Interesting
  42. 12 min later

  43. 1:36:50 · watch on youtube.com↗

    Our reading

    A tiny fraction of ancestry can carry the most important thing about a population: Yamnaya is only a few percent of DNA in India and yet it brought the language.

    Their wordsbut it is the tracer dye, right? Like it tracks into European languages and important aspects of Indo-European culture are coming through Yamnaya.
    Interesting
  44. 6 min later

  45. 1:43:00 · watch on youtube.com↗

    Our reading

    Reproductive incompatibility between diverging human lineages grows roughly as the square of their separation time, because it takes pairs of interacting genes.

    Their wordsthere's as populations become more apart, there begins to be biological incompatibilities rapidly developing, probably as the square of the distance separation, because you need pairs of interacting genes, and therefore it's the square of the separation.
    Interesting
  46. 4 min later

  47. 1:46:34 · watch on youtube.com↗

    Our reading

    The accepted model of how archaic and modern humans relate has been accreted and patched rather than built, and is due for a simpler replacement.

    Their wordsI think that, you know, the model that we've put together collectively about the relationships between archaic and modern humans is sort of accreted over time. There was this, you know, idea that modern humans are distinct and that Neanderthals and Denisovans are like sisters of each other. And then over time we developed and detected additional mixture events like this modern human into Neanderthal and then this other ones I didn't even talk about like super divergent lineage going into Denisovans and like all this other stuff.
    Interesting
  48. 8 min later

  49. 1:54:40 · watch on youtube.com↗

    Our reading

    Coming into a project with a guess about what the data will show has, again and again, turned out to be wrong.

    Their wordsThe work that I've been involved in is consistently shown that I was wrong in my biases coming into the work and I've really been almost traumatized by this. Like again and again I've come into a project with some kind of guess about what the data was showing and then the data doesn't show that.
    Interesting
  50. 12 min later

  51. 2:06:35 · watch on youtube.com↗

    Our reading

    A selection signal can be validated without a significance threshold, by measuring how far it is enriched for mutations an entirely independent study says affect a trait.

    Their wordsOur interpretation of this result is that once you slide the statistic above five, essentially all the signals of natural selection are real.
    Interesting