Genetics

Open the episode, then seek to 0:00.

Reich explains why detecting selection needs many ancient samples and distinguishes it from reconstructing population relationships.

Natural selection

Research note: Changing allele frequencies require a model of migration →

Open the episode, then seek to 5:00.

Reich distinguishes random change, migration and directional selection, explaining why ancestry shifts can complicate interpretation.

Natural selection

Open the episode, then seek to 10:00.

Reich explains how allele-specific trends and independent trait associations help distinguish selection from population movement.

Selection methods

Open the episode, then seek to 15:00.

Reich reports stronger selection in the sampled Bronze Age period and considers changing environments as possible explanations.

Bronze Age selection

Open the episode, then seek to 19:17.

Reich discusses a changing TYK2 trajectory and proposes tuberculosis pressure as a speculative explanation for its later decline.

Immune evolution

Research note: An immune variant can suggest a historical pressure →

Open the episode, then seek to 23:15.

Reich describes selected variants related to metabolism and blood traits, then discusses why short recent histories offer limited detection power.

Natural selection

Open the episode, then seek to 28:00.

Reich explains polygenic predictors from modern association studies and discusses their application to ancient samples.

Polygenic scores

Open the episode, then seek to 33:00.

Patel and Reich discuss how migration and selection affect polygenic predictors, then consider the demands of hunter-gatherer life.

Polygenic scores

Open the episode, then seek to 37:44.

Reich describes the Icelandic education-associated score result and discusses possible behavioural explanations and cross-population checks.

Polygenic scores

Research note: An education-associated score is a statistical predictor →

Open the episode, then seek to 44:20.

Patel and Reich speculate about trade-offs between cognition and other traits; Reich distinguishes reproductive success from socially valued outcomes.

Evolutionary trade-offs

Open the episode, then seek to 49:00.

Reich discusses possible reasons selection on one trait might oppose another, while treating the explanations as hypotheses.

Evolutionary trade-offs

Open the episode, then seek to 52:23.

Reich discusses changing body-fat predictors and distinguishes persistent food availability from occasional severe famine.

Evolutionary trade-offs

Open the episode, then seek to 55:55.

Reich contrasts selection on existing variation with waiting for new mutations and discusses population size and evolutionary timescales.

Natural selection

Open the episode, then seek to 1:00:55.

Reich considers whether a universal recent genetic change explains modern behaviour and distinguishes that scenario from polygenic change.

Human origins

Research note: Absence of one sweep signature does not exclude evolution →

Open the episode, then seek to 1:05:55.

Reich discusses shared human capacities and describes selection detected in the study’s sampled populations.

Human origins

Open the episode, then seek to 1:09:01.

Patel and Reich consider climatic stability as a possible explanation for agriculture’s timing, while acknowledging uncertainty.

Agriculture

Open the episode, then seek to 1:13:20.

Reich distinguishes genetic evidence from speculative explanations of farming’s timing; Patel raises comparisons with later technological development.

Agriculture

Open the episode, then seek to 1:17:00.

Reich explains discordant mitochondrial, Y-chromosomal and genome-wide relationships among modern humans, Neanderthals and Denisovans.

Archaic human ancestry

Research note: Mitochondrial history is only part of ancestry →

Open the episode, then seek to 1:22:00.

Reich sketches a speculative expansion-and-mixture model intended to connect Neanderthal and modern-human histories.

Archaic human ancestry

Open the episode, then seek to 1:27:00.

Reich connects his proposed expansion with archaeological patterns and explains how extensive local admixture could alter ancestry.

Archaic human ancestry

Open the episode, then seek to 1:32:00.

Reich discusses uncertain African population structure and uses later migrations as analogies for cultural influence despite diluted ancestry.

African population history

Research note: Deep structure does not uniquely identify an archaic population →

Open the episode, then seek to 1:37:11.

Reich considers sex-biased expansion and acknowledges difficulties explaining both maternal and paternal lineages with the same scenario.

Archaic human ancestry

Open the episode, then seek to 1:41:33.

Reich discusses possible biological barriers and Patel questions whether similar technologies require shared population history.

Archaic human ancestry

Open the episode, then seek to 1:45:56.

Reich uses an astronomy analogy to discuss how accumulated assumptions can make a historical model increasingly complicated.

Selection methods

Open the episode, then seek to 1:49:27.

Reich compares genetic and archaeological clues while stressing that the proposed shared expansion remains uncertain.

Archaic human ancestry

Research note: A unifying story still needs independent tests →

Open the episode, then seek to 1:54:15.

Reich revisits earlier selection studies, describes the enlarged dataset and explains why his expectations changed.

Selection methods

Open the episode, then seek to 1:59:15.

Reich explains how genetic relatedness informs predicted allele frequencies and how the model tests for additional time-associated change.

Selection methods

Open the episode, then seek to 2:04:15.

Reich describes independent trait-association checks, selection thresholds and tests addressing background selection and other possible confounders.

Selection methods

Research note: More detected signals need not mean evolution suddenly changed →

Open the episode, then seek to 2:09:15.

Reich explains targeted enrichment of human DNA and discusses how laboratory efficiency supports larger ancient-DNA datasets.

Ancient DNA methods