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Kindle Notes & Highlights
by
David Reich
Read between
March 10 - April 3, 2019
Although they have not left unmixed descendants, the Ancient North Eurasians have in fact been extraordinarily successful.
more than half the world’s population derives between 5 percent and 40 percent of their genomes from the Ancient North Eurasians.
The genome revolution has taught us that great mixtures of highly divergent populations have occurred repeatedly.6 Instead of a tree, a better metaphor may be a trellis, branching and remixing far back into the past.
At the end of 2013, Eske Willerslev and his colleagues published genome-wide data from the bones of a boy who had lived at the Mal’ta site in south-central Siberia around twenty-four thousand years ago.
The Mal’ta genome has now become the prototype sample for the Ancient North Eurasians. Paleontologists would call it a “type specimen,” the individual used in the scientific literature to define a newly discovered group.
Native Americans derive about a third of their ancestry from the Ancient North Eurasians, and the remainder from East Asians.
Prior to the genome revolution, I, like most others, had assumed that the big genetic clusters of populations we see today reflect the deep splits of the past. But in fact the big clusters today are themselves the result of mixtures of very different populations that existed earlier.
There was never a single trunk population in the human past. It has been mixtures all the way down.
the ancestry of the first European farmers was distinct from European hunter-gatherers in some way.
Present-day Europeans and Near Easterners are mixed: they carry within them ancestry from a divergent Eurasian lineage that branched from Mal’ta, European hunter-gatherers, and East Asians before those three lineages separated from one another.
Lazaridis called this lineage “Basal Eurasian” to denote its position as the deepest split in the radiation of lineages contributing to non-Africans.
this ghost population contributed about a quarter of the ancestry of present-day Europeans and Near Easterners. It also contributed comparable proportions of ancestry to Iranians and Indians.
No one has yet collected ancient DNA from the Basal Eurasians.
An extraordinary feature of the Basal Eurasians compared to all other lineages that have contributed to present-day people outside of Africa is that they harbored little or no Neanderthal ancestry.
the less Basal Eurasian ancestry a non-African person has, the more Neanderthal ancestry he or she has.
wherever the Neanderthal admixture occurred, it seems to have largely happened after the other branches of the non-African family tree separated from Basal Eurasians.
peoples who lived ten thousand years ago or more in what are now Iran and Israel each had around 50 percent Basal Eurasian ancestry,11 despite the clear genetic evidence that these two populations had been isolated from one another for tens of thousands of years.12 This suggests the possibility that there were multiple highly divergent Basal Eurasian lineages coexisting in the ancient Near East, not exchanging many migrants until farming expanded.
is possible that they may have sojourned in North Africa, which is difficult to reach from southern parts of the African continent because of the barrier of the Sahara Desert, and which is more ecologically linked to West Eurasia.
Today, the peoples of North Africa owe most of their ancestry to West Eurasian migrants, making the deep genetic past in that region difficult to discern.
ancient cultures there that could potentially have corresponded to the Basal Eurasians. The Nile Valley, for example, has been occupied by humans for the entire period since present-day Eurasians diverged from their closest relatives in sub-Saharan Africa.
With data from present-day people, it is difficult to probe further back in time than the most recent mixture event.
In 2016, the lid of Pandora’s box opened wide, and a whole mob of ancient ghosts whirled out. My laboratory assembled genome-wide data from fifty-one ancient modern humans in Eurasia, most of them from Europe, who lived between forty-five thousand and seven thousand years ago.
Last Glacial Maximum—which occurred between twenty-five thousand and nineteen thousand years ago—when glaciers covered the northern and middle latitudes of Europe so that all humans there lived in refuges in its southern peninsulas.
Around thirty-nine thousand years ago, a supervolcano near present-day Naples in Italy dropped an estimated three hundred cubic kilometers of ash across Europe, separating archaeological layers preceding it from those that succeeded it.
Many modern humans disappeared as dramatically as their Neanderthal contemporaries.
during the entire period from around thirty-seven thousand to around fourteen thousand years ago, almost all the individuals she analyzed from Europe could be rather well described as descending from a single common ancestral population that had not experienced mixture with non-European populations.
Archaeologists have shown that after the volcanic eruption around thirty-nine thousand years ago, a modern human culture spread across Europe making stone tools of a type known as Aurignacian, and that this replaced the diverse stone toolmaking styles that existed before. Thus genetic and archaeological evidence both point to multiple independent migrations of early modern human pioneers into Europe, some of which went extinct and were replaced by a more homogeneous population and culture.
Event Three was the coming of the people who made Gravettian tools, who dominated most of Europe between around thirty-three thousa...
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most of their ancestry derived from the same sublineage of European hunter-gatherers as the thirty-seven-thousand-year-old individual from far eastern Europe, and that they then spread west, displacing the sublineage associated with Aurignacian tools and represented in the thirty-five-thousand-year-old Belgian individual.
Event Four was heralded by a skeleton from present-day Spain dating to around nineteen thousand years ago—one of the first individuals known to be associated with the Magdalenian culture, whose members over the next five thousand years migrated to the northeast out of their warm-weather refuge, chasing the retreating ice sheets into present-day France and Germany.
The Aurignacian lineage had not died out, but instead had persisted in some geographic pocket, possibly in western Europe, before its resurgence at the end of the ice age.
Event Five happened around fourteen thousand years ago, during the first strong warming period after the last ice age, a major climatic change known as the Bølling-Allerød.
the Alpine glacial wall that extended down to the Mediterranean Sea near present-day Nice finally melted after about ten thousand years of dividing the west and east of Europe. Plants and animals from southeastern Europe (the Italian and Ba...
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After around fourteen thousand years ago, a group of hunter-gatherers spread across Europe with ancestry quite different from that of the people associated with the preceding Magdalenian culture, whom they largely displaced.
But after around fourteen thousand years ago, western European hunter-gatherers became much more closely related to present-day Near Easterners. This proved that new migration occurred between the Near East and Europe around this time.
The people who had waited out the ice age in southern Europe became dominant across the entire European continent following the melting of the Alpine glacial wall.26 Perhaps these same people also expanded east into Anatolia, and their descendants spread farther to the Near East, bringing together the genetic heritages of Europe and the Near East more than five thousand years before farmers spread Near Eastern ancestry back into Europe by migrating in the opposite direction.
Today, the peoples of West Eurasia—the vast region spanning Europe, the Near East, and much of central Asia—are genetically highly similar.
The physical similarity of West Eurasian populations was recognized in the eighteenth century by scholars who classified the people of West Eurasia as “Caucasoids” to differentiate them from East Asian “Mongoloids,” sub-Saharan African “Negroids,” and “Australoids” of Australia and New Guinea.
The most common way to measure the genetic similarity between two populations is by taking the square of the difference in mutation frequencies between them, and then averaging across thousands of independent mutations across the genome to get a precisely determined number.
Measured in this way, populations within West Eurasia are typically around seven times more similar to one another than West Eurasians are to East Asians.
Farming began between twelve and eleven thousand years ago in southeastern Turkey and northern Syria, where local hunter-gatherers began domesticating most of the plants and animals many West Eurasians still depend upon today, including wheat, barley, rye, peas, cows, pigs, and sheep. After around nine thousand years ago, farming began spreading west to present-day Greece and roughly at the same time began spreading east, reaching the Indus Valley in present-day Pakistan. Within Europe, farming spread west along the Mediterranean coast to Spain, and northwest to Germany through the Danube
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Matthias Meyer,
enriching DNA extracted from ancient bones for human sequences of interest.28 This approach makes ancient DNA analysis up to one thousand times more cost-effective and gives access to samples that would otherwise provide too little DNA to study.
the inner-ear part of the skull—known as the petrous bone—preserves a far higher density of DNA than most other skeletal parts, up to one hundred times more for each milligram of bone powder.
anthropologist Ron Pinhasi, working in Dublin,
the mother lode of DNA is found in the cochlea, the snail-shap...
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The farmers of the western mountains of Iran, who may have been the first to domesticate goats, were genetically directly derived from the hunter-gatherers who preceded them. Similarly, the first farmers of present-day Israel and Jordan were descended largely from the Natufian hunter-gatherers who preceded them.
the degree of genetic differentiation between the first farmers of the western part of the Near East (the Fertile Crescent, including Anatolia and the Levant) and the first farmers of the eastern part (Iran) was about as great as the differentiation between Europeans and East Asians today.
about ten thousand years ago there were at least four major populations in West Eurasia—the farmers of the Fertile Crescent, the farmers of Iran, the hunter-gatherers of central and western Europe, and the hunter-gatherers of eastern Europe. All these populations differed from one another as much as Europeans differ from East Asians today.
the farmers of the Near East began migrating and mixing with their neighbors. But instead of one group displacing all the others and pushing them to extinction, as had occurred in some of the previous spreads of hunter-gatherers in Europe, in the Near East all the expanding groups contributed to later populations.
