Mystery invaders conquered Europe at the end of last ice age

https://www.newscientist.com

DNA was taken from ancient human bones, like this skull, 

from the Dolnte Vestonice burial site in the Czech Republic

L. Lang

Europe went through a major population upheaval about 14,500 years ago, at the end of the last ice age, according to DNA from the bones of hunter-gatherers.
Ancient DNA studies published in the last five years have transformed what we know about the early peopling of Europe. The picture they paint is one in which successive waves of immigration wash over the continent, bringing in new people, new genes and new technologies.
These studies helped confirm that Europe’s early hunter-gatherers – who arrived about 40,000 years ago – were largely replaced by farmers arriving from the Middle East about 8000 years ago. These farmers then saw an influx of pastoralists from the Eurasian steppe about 4500 years ago, meaning modern Europe was shaped by three major population turnover events.

Waves of immigration

The latest study suggests things were even more complicated. About 14,500 years ago, when Europe was emerging from the last ice age, the hunter-gatherers who had endured the chilly conditions were largely replaced by a different population of hunter-gatherers.

Exactly where this new population came from is still unclear, but it seems likely that they came from warmer areas further south. “The main hypothesis would be glacial refugia in south-eastern Europe,” says Johannes Krause at the Max Planck Institute for the Science of Human History in Jena, Germany, who led the analysis.
As conditions improved, it was these southern hunter-gatherers who took advantage and migrated into central and northern Europe, he says – meaning there was a genetic discontinuity with the hunter-gatherer populations that had lived there earlier.

Martin Frouz

His team analysed mitochondrial DNA extracted from 55 ancient Europeans, the oldest of whom lived 35,000 years ago – during the Pleistocene – and the youngest just 7000 years ago, during the Holocene. Previous studies focused largely on the Holocene, looking at human remains from the last 10,000 years.
“This is the first glimpse at Pleistocene population dynamics in Europe,” says Krause. “Little has been done on this older material, mostly due to lower abundance of material and lesser preservation due to age.”
“The population turnover after 14,500 years ago was completely unexpected,” says Iosif Lazaridis at the Harvard Medical School in Boston. “It seems that the hunter-gatherers of Europe braved the worst of the ice age during the last glacial maximum but were then replaced when the ice age had begun to subside.”

Europe’s unusual history

The picture is not yet clear, however, as the study only looked at mitochondrial DNA sequences, rather than the longer nuclear DNA of other studies. “Mitochondrial DNA tells only part of the story of a population,” says Lazaridis. It is important to try to extract nuclear sequences from the Pleistocene-aged skeletons to find out more about this earlier population turnover, he says.
The work also may solve a long-standing mystery of why a certain genetic signature is missing in people of European ancestry. All people today are members of one of a relatively small number of distinct groups based on their mitochondrial DNA, which is passed down the maternal line. The distribution of people in each group gives us a sense of how humans spread across the world in prehistory.
It always seemed that Europe had a very unusual history of colonisation because one major haplogroup – the M clade – is almost entirely missing, despite being very common across Asia and even found in Native Americans. Instead, another major haplogroup – the N clade – is most common.
“Some authors had argued that the M and N haplogroups represented two different dispersal events from Africa,” says Toomas Kivisild at the University of Cambridge.
But Krause and his colleagues found that the M clade might actually have been common in Europe before the population turnover 14,500 years ago: three of the 18 most ancient humans they studied belonged to the M clade.
This suggests that the initial colonisation of Europe and Asia may have involved the same ancient population – and that the M group was actually lost in Europe much later, perhaps connected in some way to the mystery upheavals 14,500 years ago.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2016.01.037
Read more: The three ancestral tribes that founded Western civilisation

 http://arstechnica.com/

Scientific Method / Science & Exploration

There was a massive population crash in Europe over 14,500 years ago

New evidence shows a whole group of Europeans vanished, replaced by people of unknown origins.

by Annalee Newitz - Feb 4, 2016 6:35pm CST

Europe wasn't a very hospitable place fifteen millennia ago. The westernmost landmass of the Eurasian continent had endured a long ice age, with glaciers stretching across northern Europe and into the region we now call Germany. But suddenly, about 14,500 years ago, things started to warm up quickly. The glaciers melted so fast around the globe that they caused sea levels to rise 52 feet in just 500 years. Meanwhile, the environment was in chaos, with wildlife trying vainly to adjust to the rapid fluctuations in temperature. Humans weren't immune to the changes, either.
A new, comprehensive analysis of ancient European DNA published today in Current Biology magazine by an international group of researchers reveals that this period also witnessed a dramatic shift in the human populations of Europe. Bloodlines of hunter-gatherers that had flourished for thousands of years disappeared, replaced with a new group of hunter-gatherers of unknown origin.
Researchers discovered this catastrophic population meltdown by sequencing the mitochondrial DNA of 35 people who lived throughout Europe between 35 and 7 thousand years ago. Mitochondrial DNA is a tiny amount of genetic material that's inherited virtually unchanged via the maternal line, and thus it serves as a good proxy for relatedness over time. Two people from the same maternal stock share almost the same mitochondrial DNA, even if separated by thousands of years, because this kind of DNA evolves very slowly.
It's long been known that two such related groups, called M clade and N clade, poured out of Africa and across the Eurasian continent about 55 thousand years ago. Some of these people wandered so far that they even made it to Australia, eventually. And yet something rather odd happened to the people of Europe. Only members of the N clade survived into the present day, while Asia, Australia, and the Americas are full of the offspring of both N and M. Until the new study in Current Biology, scientists believed that the most likely explanation was that roughly 45 thousand years ago, Europe was colonized solely by the N clade, while both clades settled elsewhere around the world.
But thanks to sequencing the mitochondrial DNA in those 35 ancient people, the researchers uncovered something previously unknown. There were, in fact, people from the M clade alive in Europe as recently as 25 thousand years ago. But something happened to wipe them out during the cold, dry glacial maximum that gripped the world between 25 and 14.5 thousand years ago.

Enlarge / In this image, you can see the clades of the people

 who the team sequenced, and how they fared over time. The

 R and U clades are all descended from the N clade. Note that

 M is present until 25 thousand years ago, when the ice age begins.

Current Biology

There are obvious reasons why Europeans might have suffered a population bottleneck during the ice age, or the Last Glacial Maximum. Food was scarce, and once-fecund habitats became unlivable. Groups that once roamed the wide-open fields of Europe retreated into small refuges, separated by walls of ice or frozen drought wastelends created when glaciation locks up atmospheric water. The researchers believe that the M clade, whose members were found far to the north, may have slowly died out during that period. After the glaciers retreated, the survivors were replaced by a new N-related population from elsewhere on the continent.
Write the researchers:

The potential impact of climatic events on the demography, and thus the genetic diversity of early Europeans, has previously been difficult to quantify, but it likely had consequences for the relative components of ancient ancestry in modern-day populations. Our demographic modeling reveals a dynamic history of hunter-gatherers, including a previously unknown major population shift during the Late Glacial interstadial (the BøllingAllerød, 14.5 ka). Under our best-fitting model, the small initial founder population of Europe slowly grows up until 25 ka and survives with smaller size in LGM [Last Glacial Maximum] climatic refugia (25–19.5 ka) before re-expanding as the ice sheets retract. Although this model supports population continuity from pre- to post-LGM, the genetic bottleneck is consistent with the apparent loss of hg M in the post-LGM. Globally, the early warming phases of the Late Glacial are strongly associated with substantial demographic changes, including extinctions of several megafaunal species and the first expansion of modern humans into the Americas. In European hunter-gatherers, our model best explains this period of upheaval as a replacement of the post-LGM maternal population by one from another source.

Essentially, an entire genetic line in Europe was wiped out by climate change. You might say that today's European population still bears the scars of an ancient ice age in its mitochondrial DNA.
Current Biology, 2016. DOI: 10.1016/j.cub.2016.01.037.

Why Did Ancient Europeans Just Disappear 14,500 Years Ago?

By Tia Ghose March 2, 2016 11:22 AM

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 The skull of a man who lived between 36,200 

and 38,700 years ago in Kostenki in western Russia.

 

Some of Europe's earliest inhabitants mysteriously vanished toward the end of the last ice age and were largely replaced by others, a new genetic analysis finds.

The finds come from an analysis of dozens of ancient fossil remains collected across Europe.
The genetic turnover was likely the result of a rapidly changing climate, which the earlier inhabitants of Europe couldn't adapt to quickly enough, said the study's co-author, Cosimo Posth, an archaeogenetics doctoral candidate at the University of Tübingen in Germany.
 [Top 10 Mysteries of the First Humans]
The temperature change around that time was "enormous compared to the climactic changes that are happening in our century," Posth told Live Science. "You have to imagine that also the environment changed pretty drastically."
A twisted family tree
Europe has a long and tangled genetic legacy. Genetic studies have revealed that the first modern humans who poured out of Africa, somewhere between 40,000 and 70,000 years ago, soon got busy mating with local Neanderthals. At the beginning of the agricultural revolution, between 10,000 and 12,000 years ago, farmers from the Middle East swept across Europe, gradually replacing the native hunter-gatherers. Around 5,000 years ago, nomadic horsemen called the Yamnaya emerged from the steppes of Ukraine and intermingled with the native population. In addition, another lost group of ancient Europeans mysteriously vanished about 4,500 years ago, a 2013 study in the journal Nature Communications found.
But relatively little was known about human occupation of Europe between the first out-of-Africa event and the end of the last ice age, around 11,000 years ago. During some of that time, the vast Weichselian Ice Sheet covered much of northern Europe, while glaciers in the Pyrenees and the Alps blocked east-west passage across the continent.
Lost lineages
To get a better picture of Europe's genetic legacy during this cold snap, Posth and his colleagues analyzed mitochondrial DNA — genetic material passed on from mother to daughter — from the remains of 55 different human fossils between 35,000 and 7,000 years old, coming from across the continent, from Spain to Russia. Based on mutations, or changes in this mitochondrial DNA, geneticists have identified large genetic populations, or super-haplogroups, that share distant common ancestors.
"Basically all modern humans outside of Africa, from Europe to the tip of South America, they belong to these two super-haplogroups that are M or N," Posth said. Nowadays, everyone of European descent has the N mitochondrial haplotype, while the M subtype is common throughout Asia and Australasia.
The team found that in ancient people, the M haplogroup predominated until about 14,500 years ago, when it mysteriously and suddenly vanished. The M haplotype carried by the ancient Europeans, which no longer exists in Europe today, shared a common ancestor with modern-day M-haplotype carriers around 50,000 years ago.
The genetic analysis also revealed that Europeans, Asians and Australasians may descend from a group of humans who emerged from Africa and rapidly dispersed throughout the continent no earlier than 55,000 years ago, the researchers reported Feb. 4 in the journal Current Biology.
Time of upheaval
The team suspects this upheaval may have been caused by wild climate swings.
At the peak of the ice age, around 19,000 to 22,000 years ago, people hunkered down in climactic "refugia," or ice-free regions of Europe, such as modern-day Spain, the Balkans and southern Italy, Posth said. While holdouts survived in a few places farther north, their populations shrank dramatically.
Then around 14,500 years ago, the temperature spiked significantly, the tundra gave way to forest and many iconic beasts, such as woolly mammoths and saber-toothed tigers, disappeared from Eurasia, he said.

For whatever reason, the already small populations belonging to the M haplogroup were not able to survive these changes in their habitat, and a new population, carrying the N subtype, replaced the M-group ice-age holdout, the researchers speculate.

Exactly where these replacements came from is still a mystery. But one possibility is that the newer generation of Europeans hailed from southern European refugia that were connected to the rest of Europe once the ice receded, Posth speculated. Emigrants from southern Europe would also have been better adapted to the warming conditions in central Europe, he added.