Genetics, Language, and the Prehistory of

the Americas

Alan R. Rogers

April 2, 2018

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Outline

I Three waves of migration or one?

I Paleoamerican hypothesis

I Population growth in South America

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Joseph Greenberg Hypothesis

Greenberg advocatedcomparing many languages ata time, using a small list ofslowly-changing words, todetect deep relationships.

Divided Amerindian languagesinto 3 major groups—Amerind,Na-Dene (includingAthabascan), andEskimo-Aleut—which in hisview descend from 3 waves ofmigration into the Americas.

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Dispute

Most linguists don’t acceptGreenberg’s method.

In their view, linguistic data arenot informative that far back inthe past.

Instead of 3 major groups, theyrecognize 150–180 independentlanguage families.

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Raghavan et al (2015) Study

Sequenced 31 modernAmerindian genomes and 23ancient genomes. Also usedpreviously-published genomes.

SNP chip genotypes from 79individuals from 28populations.

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Early North Am. similar to modern South Am.

Next few slides compare DNA of ancient fossils with that ofmodern Amerindians.

General pattern: early fossils are genetically similar to modernAmerindians farther south.

Later fossils are similar to modern Amerindians of their ownregion.

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Pleistocene Anzick-1 fossil most similar to S

Americans

Anzick fossil, ofClovis culture,was found inMontana.

DNA most similar to S American populations.

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Early Holocene Kennewick fossil

∼8.5 ky old,fromWashingtonstate

DNA similar toAmerindiansthroughout USand S America.

Not more similar to Amerindians of its own region, the PacificNorthwest.

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A 6000 year old fossil

DNA still similar to Amerindians throughout US and SAmerica.

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A 5500 year old S American fossil

More similar to Amerindians of S America.

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A 3500 year old S American fossil

Most similar to Amerindians of its own region of S America.

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A ∼500 year old Mexican fossil

Most similar to Amerindians of Mexico.

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A ∼400 year old fossil from US Northeast

Most similar to Amerindians of US SW and Mexico.

An exception to the general rule.

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A ∼200 year old fossil from Tierra del Fuego

Most similar to Amerindians of Tierra del Fuego

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Population Relationships

Consistent with Greenberg hypothesis; Anzik & Karitiana(Amerind) are related to Athabascan (Na Dene) and (lessclosely) to Inuit and Saqqaq (Eskimo-Aleut).

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Dating the Asian-Amerindian Split

Comparing two Amerindianpopulations with the Koryak ofeastern Siberia.

Upper panel: Karitiana are a SAmerican population thatspeaks an Amerind language(in Greenberg’s classification).

Lower panel: Athabascan ispart of Greenberg’s Na-Denelanguage family.

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Split date contradicts GreenbergVertical axis estimatescumulative frequency ofcoalescent events.

Red: estimated from geneticdata

Blue: best-fitting modelwithout migration

Red: best-fitting model withmigration

Amerinds and Athabascansboth separated from Asiansabout 20 kya.

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Separation wasn’t sudden

TB generations ago, theancestral population changessize.

TDIV generations ago, it splits intwo, but the subdivisionscontinue exchanging migrants.

TM generations ago, migrationstops.

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Colonization of the Americas

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Outline

◦ Three waves of migration or one?

I Paleoamerican hypothesis

I Population growth in South America

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Paleoamerican Model (Gonzalez et al 2008)

I Earliest American fossils differ in skull shape from laterones.

I More like modern Australians and Melanesians.

I These earliest Americans were mostly replaced byAmerindians who arrived later.

I Evidence is from early skeletons and a few historical relictpopulations, now extinct: the Pericues and theFuego-Patagonians.

I Hypothesis predicts these populations should have DNAlike Australians and Melanesians, not Amerindians.

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Testing the Paleoamerican modelPrincipalcomponents plot.

ModernAmerindians arethe blurry bluepoints in theupper left.

AncientAmerindians,including Pericuesand Fuego-Patagonians,

plot with modern Amerindians. No ancient Amerindians withOceanians.

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Testing the Paleoamerican model

Pericues & Fuego-Patagonians have DNA like Amerindians,not like Oceanians.

Refutes Paleoamerican hypothesis. (Raghavan et al 2015)

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Outline

◦ Three waves of migration or one?

◦ Paleoamerican hypothesis

I Population growth in South America

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South American archaeological sites

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Density of radiocarbon dates (Goldberg et al 2016)

Radiocarbon dates serve as proxy for population size.

No information in the Amazon basin.

Coastal population growth accelerates after 5 kya.

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Temperature and population

a, temperature; b, radiocarbondensity; c, frequency of sites.

Early growth; crash at 11 kya;plateau during 10–6 kya; thenmore growth.

Megafauna went extinct 11 kya;sedentary agriculture began5.5–3.5 kya.

1000-year oscillations duringplateau. Don’t know why.

(Goldberg et al 2016)

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Fitting a model

Top: growth rate;Bottom: population size.

Before 6 kya, growthrate declines aspopulation increases.

After 6 kya, growth ratestable as populationincreases.

(Goldberg et al 2016)

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Summary

I All Amerindians, including ancient ones, separated fromAsians about 22 kya.

I Separation wasn’t sudden.

I Na-Dene (incl Athabascans) separated from Amerindsabout 13 kya.

I Regional genetic differences developed gradually, overthousands of years.

I Paleoamerican hypothesis is false: earliest Americans notrelated to Oceanians.

I Population history of South American: initial growthleading to a plateau, then renewed growth afteragriculture.

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