Ancient DNA reveals well-kept secrets about the migrations, evolution and interbreeding of human populations, but also about the history of pathogens and animals. Fifth and last article in this series on the bubbling science that is paleogenomics.
Where do we come from ? The first ones Homo sapiens appeared in Africa perhaps 300,000 years ago. Our species then spread to Eurasia, where it encountered other hominids, all of which have since disappeared. It took another tens and tens of thousands of years to find our ancestors in the Americas.
Indigenous peoples have their legends to explain their presence here. The populating of the continent is the subject of debate in the scientific community with archaeologists, anthropologists, linguists, paleoclimatologists and, now, geneticists at the forefront of discussions. The fundamental questions relate to the origin of the migrants, their method of movement (on foot or by boat) and the speed of their dissemination.
After the discovery of the Clovis site (named after a town in New Mexico) in 1929, it was believed that the first humans arrived in America in a single wave, around 13,000 years ago, through Beringia, following the migrations of large animals. The name derived from the Bering Strait refers to a land bridge that existed between Siberia and Alaska after the last glacial maximum. The Quaternary glaciations then lowered the sea level by more than 100 meters compared to the current level in this part of the world. The Clovis First hypothesis stated that arrowheads found in New Mexico, and then throughout the continent, testified to a single original population.
New archaeological discoveries, increasingly fine dating and genetic research have enriched the portrait and made it possible to understand that our ancestors of the Clovis culture were not the first on the continent.
“For ten or fifteen years, genetics has completely changed our interpretation of the history of humans coming out of Africa,” summarizes Ariane Burke, professor in the Department of Anthropology at the University of Montreal. Discoveries based on genetics also allow us to better understand the diversity of humans geographically separated from each other. »
Humanity’s family tree now resembles a complex phylogenetic bush. Genetics has even made it possible to understand DNA exchanges between human species that have lived side by side for tens of thousands of years. European descendants carry about 2% Neanderthal genes. “Our history over the past 300,000 years is much richer and more complicated than previously thought,” adds Professor Burke.
A certainty, a hypothesis
The professor herself is interested in the Middle Paleolithic (-300,000 to -400,000 years before the present), the last glacial maximum (about -20,000 years) and the mode of dispersal of populations in prehistory. It speaks of a certainty and a hypothesis concerning the origin of the Aboriginals here.
“There is certainty now that the indigenous populations of Central and South America come from Central Asia,” she says. Genetically, we can trace their roots to Central Asia. Genetically, they are well rooted. »
The hypothesis still in debate is said to be the ” Standstill Hypothesis » or even status quo Beringian. We also talk about the model of incubation in Beringia (IMB for the pros). This idea dates back to the 1930s and has been strongly supported by recent research and discoveries in genetics.
Paleogeneticists have understood that a certain number of genetic mutations appear in the New World without being present elsewhere, in Siberia for example. This observation suggests that a stem population isolated long enough by climate change for several thousand years then dispersed in the Americas when the retreat of the glaciers made it possible to penetrate the continent, i.e. approximately 15,000 years ago. .
“It is proposed that these humans were in Eastern Siberia, where the Bering Strait is now and part of Alaska and the Yukon, summarizes Mr.me Burke. Perhaps the Last Glacial Maximum isolated them for thousands of years from the original population in Central Asia and then dispersed to the Americas. It is a hypothesis on genetic bases which remains to be tested, because we have very little archaeological data. »
The flooding of much of Beringia and coastal areas does not facilitate research. Neither is the likely size of the ancient population.
lessons from the past
From the field, Ariane Burke does not stop doing it. She gave the phone interview in early summer from Spain, where her teams were testing predictions from their climate models and archaeological models that could indicate where in Europe during the last glacial maximum the territories were located. most viable for humans. The excavations carried out in June were concentrated in the central zone of the Iberian Peninsula, deemed at first glance not conducive to human settlements.
The Montreal professor is also attached as a visiting researcher to the Oeschger Center for Climate Change Research, in Bern, Switzerland. A concordance is thus established between research on very remote times and very current problems. “I try to shed light on the present, like many archaeologists elsewhere. In the past, people have experienced very abrupt climatic changes. They survived. They may have lessons to teach us about the changes already underway. »
When she was a student specializing in archaeozoology in 1990, Ms.me Burke herself excavated the Bluefish Caves in northern Yukon. She actually says “one thousand nine hundred and ninety”, Belgian style. Twenty years later, his own doctoral student Lauriane Bourgeon resumed and completed the studies on two of the three caves of the site reputed to house the oldest and best preserved archaeological remains (for this period) in Canada. There are bones of mammoths, horses, mink, caribou, sheep, birds, fish, bears and even lions.
“Lauriane, who is now the DD Bud, made the discoveries of cut marks, explains Mr.me Burke. Finding traces of cutting on bones is already an indication of human presence. We dated the bones. It was concluded that the site was probably used for several periods, including the last glacial maximum. It could be a small clue of the existence of this famous original population. It would have been prevented from migrating south by glaciers and west to Siberia. »
Even older traces of settlement have been identified. Still in New Mexico, researchers from the University of Texas recently established that a large pile of mammoth bones dated from 36,250 to 38,900 years ago. No stone tools were found there, but the bones show some marks typical of rendering and roasting.
In 2021, French academics claimed to have found human traces at eight Brazilian sites occupied from 13,000 to 40,000 before today. The most skeptical do not believe it and note that no human remains confirm the hypotheses.
The convergence of evidence becomes essential in this multi-millennial quest. Genetics or linguistics can provide very solid leads, which archeology can then establish with artefacts. “Attractive hypotheses compete,” says specialist Burke. To untangle them requires material evidence, combining several lines of thought and showing that they are consistent with each other. For dating, it’s good to have a sample. It’s even better to have two or three, all consistent. »