Who We Are and How We Got Here - Part 2 - Ghost Populations

These vanished populations contributed genes to people living today

The Ancient North Eurasians

One of the most fascinating discoveries of recent genetic studies is the existence of various “ghost populations.” These are populations that can be reconstructed using genetic statistics but no longer exist in any form today. Their existence can be inferred by looking at the DNA of living people—including populations widely separated both geographically and chronologically.

For example, when researchers ran the Three and Four Population tests described last time, they counterintuitively found that two closely related groups were French people and pre-Columbian Native Americans: "What we had found was evidence that people in Northern Europe, such as the French, are descended from a mixture of populations, one of which shared more ancestry with present-day Native Americans that with any other population living today." (p. 79)

How could that be? Before Columbus's voyage, there was no possibility of significant gene flow between Europeans and Native Americans.

The answer turned out the be the existence of a third group of people who contributed genetic material to both Europeans and Native Americans—a group which no longer exists today. Researchers dubbed this ghost population the Ancient North Eurasians based on their presumed origin.

We know that this population lived somewhere in Central Asia and Siberia tens of thousands of years ago and were perhaps the first modern humans to occupy these places. The Ancient North Eurasians contributed significant amounts of DNA to both Western Europeans and Native Americans but do not persist as any sort of coherent, identifiable ethnic group today—neither in the region they originally inhabited nor anywhere else. The current inhabitants of Siberia are a different population more closely related to East Asians who migrated into this region much later and thus do not share ancestry with Native Americans or Western Europeans.

We proposed that more than fifteen thousand years ago, there was a population living in northern Eurasia that was not the primary ancestral population of the present-day inhabitants of the region. Some people from this population migrated east across Siberia and contributed to the population that crossed the Bering land bridge and gave rise to Native Americans. Others migrated west and contributed to Europeans.

This would explain why today, the evidence of mixture in Europeans is strong when using Native Americans as a surrogate for the ancestral population and not as strong in indigenous Siberians, who plausibly descend from more recent, post-ice age migrations into Siberia from more southern parts of East Asia.

We called this proposed new population the "Ancient North Eurasians." At the time we proposed them, they were a "ghost"—a population that we can infer existed in the past based on statistical reconstruction but that no longer exists in unmixed form.

The Ancient North Eurasians would without a doubt have been called a "race" had they lived today, as we could show that they must have been genetically about as differentiated from all other Eurasian populations who lived at the time as today's "West Eurasians," "Native Americans," and "East Asians" are from one another.

Although they have not left unmixed descendants, the Ancient North Eurasians have in fact been extraordinarily successful. If we put together all the genetic material that they have contributed to present-day populations, they account for literally hundreds of millions of genomes' worth of people. All told, more than half the world's population derives between 5 percent and 40 percent of their genomes from the Ancient North Eurasians. (pp. 79-81)

In 2013 a 24,000 year old fossil from south-central Siberia known as the Mal'ta Boy had his genetics analyzed. The findings confirmed what the DNA research earlier showed: the Mal'ta Boy was more closely related both to Europeans and Native Americans than the current occupants of Siberia. Archaeologists had found a member of the Ancient North Eurasians. Malt'ta Boy came from what archaeologists subsequently designated as the Mal'ta-Buret' culture which lived in the area west of Lake Baikal 24,000 to 15,000 years ago.

With an actual physical sample of an Ancient North Eurasian in hand, the ancestry of modern Native Americans could be reconstructed more accurately. Native Americans inherited about a third of their ancestry from this ANE population, with the remainder coming from a population more closely related East Asians. The ANE population also contributed genetically the Botai culture of prehistoric Kazakhstan and Northern Asia who appear to have been the first people to domesticate horses. They also contributed DNA to the Yamnaya culture of the Pontic-Caspian steppe, who went on to contribute significant ancestry to the present-day populations of both Europe and India as we'll see later on.

The Basal Eurasians

Another "ghost" population discovered by geneticists was dubbed the Basal Eurasians.

This population appears to be the earliest branch to split off from the ancestors of all non-Africans today. Their most distinctive trait is the total lack of any admixture with either Neanderthals or Denisovans. The Basal Eurasians contributed large portions of DNA to the people who lived in and around the ancient Near East roughly 15,000 years ago. In fact, nearly half the DNA of these populations derives from the Basal Eurasians.

Given their large genetic contribution to multiple early farming peoples in Western Asia, it is speculated that they must have lived in or around this region. However, the known presence of Neanderthals living in this area going back hundreds of thousands of years makes their lack of Neanderthal admixture perplexing.

One possibility is that they originally inhabited North Africa or the Nile Valley and migrated eastward into the Near East at some later point in time. Similarity in skull shapes and tool styles between populations of ancient North Africans and the Natufian people have fueled speculation that the Natufians—the originators of farming—were migrants into the Levant (modern-day Israel and Lebanon) from somewhere in Northern Africa, although there is no genetic evidence for that. Both the Natufians and the ancient hunter-gatherers of Iran have the highest proportions of Basal Eurasian ancestry.

A tempting idea is that the Basal Eurasians represent the descendants of a second wave of migration of modern humans north of the Sahara Dessert, well after the dispersal of the population that interbred with the Neanderthals.

However, this is not correct, as the Basal Eurasian lineage shares much of the history of other non-Africans, including descent from the same relatively small population that founded all non-African lineages more than fifty-thousand years ago.

The ancient presence of the Basal Eurasians in Eurasia becomes even clearer when one considers that peoples who lived ten thousand years ago or more in what are now Iran and Israel each had around 50 percent Basal Eurasian ancestry, despite clear genetic evidence that these two populations had been isolated from each other for tens of thousands of years.

This suggests the possibility that there were multiple highly divergent Basal European lineages coexisting in the ancient Near East, not exchanging any migrants until farming expanded. The Basal Eurasians were a major and distinctive source of human genetic variation, with multiple subpopulations persisting for a long period of time. (p. 85)

Where exactly this population lived is a mystery, Reich tells us, and unlike the Ancient North Eurasians, no fossils from anyone belonging to this population have yet been discovered.

One speculation I would offer is that they may have been descendants of a very early migration out of Africa that settled down in Persian Gulf Oasis. This was one of the first places outside of Africa to be settled by modern humans. It was a grassland refugium, rich in water and game, which would have isolated them from the surrounding populations. The geographic proximity of the Persian Gulf Oasis relative to both the Levant and Iranian plateau makes it a good candidate for the source of this population.

Between 11,400 and 8,000 years ago, rising sea levels inundated the Persian Gulf Basin forming the current Persian Gulf. Archaeologist Kenneth Rose has speculated that when the Persian Gulf Oasis was flooded, the inhabitants relocated to what is now the southern rim of the Persian Gulf and established the Sumerian civilization. He notes that Sumerian culture emerges spontaneously in the region some 7,500 years ago with basically no archaeological precedent coinciding with the inundation of the Gulf Oasis. It's also notable that the language of the Sumerians was a language isolate—a language with no discernible relationship to any other languages.

The shallow waters of the inland sea known as the Persian Gulf might well hold the evidence of the earliest human migrations out of Africa, says Jeffrey Rose, an archaeologist and researcher with the UK’s University of Birmingham. In a paper called ‘New Light on Human Prehistory in the Arabo-Persian Gulf Oasis’, published in Current Anthropology (51:6 December 2010), Rose argues that highly developed settlements arose ‘out of nowhere’ around the shores of the Gulf about 7,500 years ago. This corresponds with the flooding of the Persian Gulf basin around 8,000 years by the Indian Ocean, and the obvious conclusion is that the new settlements are those of displaced populations who escaped the inundation.

Rose has plotted some 60 new archaeological sites that appear on the shores of the Gulf after this event, where previously there had only been a handful of scattered hunting camps. ‘These settlements boast well-built, permanent stone houses, long-distance trade networks, elaborately decorated pottery, domesticated animals, and even evidence for one of the oldest boats in the world,’ Rose says, before asking: ‘how could such highly developed settlements pop up so quickly, with no precursor populations to be found in the archaeological record? These new colonists may have come from the heart of the Gulf, displaced by rising water levels that plunged the once fertile landscape beneath the waters of the Indian Ocean.’

Sea level data show that, prior to the flood, the Gulf basin would have been an ideal refuge from the harsh deserts surrounding it, with fresh water supplied by the Tigris, Euphrates, Karun, and Wadi Baton Rivers, as well as by underground springs. This well-watered and fertile landmass may well have been host to early migrants out of Africa, and would have provided ‘a sanctuary throughout the Ice Ages when much of the region was rendered uninhabitable due to hyperaridity’, Rose said.

Persian Gulf: the first migration? (World Archaeology)

Lost Civilization May Have Existed Beneath the Persian Gulf (Live Science)

It’s possible, then, that this “lost civilization” might be the source of the Basal Eurasians. This group would have been isolated from the Neanderthal populations living elsewhere in the region. Later, after the inundation of the Gulf, they could have migrated outward and contributed ancestry to the people who subsequently became the first farmers in both Israel and Iran. Form there, those farmers expanded and migrated into both Europe and India.

The flooding of the Persian Gulf has also been seen as a possible origin of the Sumerian creation myth, which became part of both the Epic of Gilgamesh and the story of Noah’s ark in the Bible. The location of this oasis and its geography also closely resemble the Biblical description and location of the Garden of Eden. The sudden appearance of the Sumerians among the Semitic-speaking peoples of the ancient Near East may also have helped kickstart civilization in this region, including the founding of cities like Eridu and Uruk which acted as places of trade and cultural transmission.

NEXT: Prehistoric Europe