Genetic Study of Romanian Skull Upends Previous Theories of Evolution
A team of researchers led by the Swedish Uppsala University geneticist Mattias Jakobsson have fully sequenced the genome of a woman who lived in Europe at least 35,000 years ago. Her DNA was extracted from a skull that was found buried in a cave called Peştera Muierii in Romania and it is one of the oldest genomes to ever be decoded in its entirety. This achievement represents a remarkable breakthrough for scientists searching for answers about humanity’s evolutionary history , which has proven to be a complex story filled with many twists and turns.
Going into this project the researchers were working under certain assumptions about who the woman (designated Peştera Muierii I) was and what her DNA might reveal, based on previous genetic research carried out on other human fossils. However several of these assumptions turned out to be false, as Jakobsson and his colleagues have revealed in a report published in the journal Current Biology . Their discoveries are both surprising and highly significant, and could have a huge impact on the study of human prehistory moving forward.
The Peştera Muierii cave, Romanian for “The Woman’s Cave”, where the skull whose DNA has been analyzed in the genetic study was found. (Cristian Bortes / CC BY 2.0 )
Genetic Study Shows Diversity of Early Europeans
It is known that modern humans originally evolved in Africa and that they only began migrating to Europe and Asia around 80,000 years ago. They did so, at least in part, because the climate in Africa was getting dryer, as a long-term consequence of the onset of the last Ice Age approximately 120,000 years ago.
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Until now it was believed that the number of people who chose to leave their African homeland was relatively small and homogenous. Consequently, their descendants in new lands would have lacked genetic diversity since their ancestors all came from a genetically limited population base. Whatever genetic diversity they did possess would decline noticeably over time, as the original migrants divided up into separate groups that mixed with each other less and less.
This theory was developed to explain the results elicited from the existing human fossil record. DNA samples taken from ancient skeletons recovered in various locations in Europe and Asia have shown a low level of diversity, in comparison to ancient skeletons recovered in Africa. But there was a flaw in this research. The human fossils analyzed previously were not as old as the skull recovered from the cave in Romania.
Mattias Jakobsson, professor at the Department of Organismal Biology at Uppsala University and one of the authors of the genetic study. ( David Naylor / Uppsala University )
A Genetic Bombshell: Understanding the Importance of the Genetic Study
The lack of diversity noted before applied exclusively to the fossilized remains of men and women who’d lived during the Last Glacial Maximum (LGM) and beyond. The Last Glacial Maximum happened between 24,000 and 19,000 years ago, and refers to the period during the last Ice Age when glaciers covered a larger percentage of the Earth than at any other time.
If the nature of the African migration was truly responsible for the lack of genetic diversity in ancient European hunter-gathers, this shouldn’t have caused any problems. The DNA sample taken from Peştera Muierii I and included in the genetic study should have demonstrated only slightly more genetic diversity than the later samples. But it didn’t.
In fact, Peştera Muierii I’s genome was highly diverse, much more diverse than genomes sequenced from European fossils that had been found thousands of years later. “She is a bit more like modern-day Europeans than the individuals in Europe 5,000 years earlier, but the difference is much less than we had thought,” Mattias Jakobsson explained in EurekaAlert. “We can see that she is not a direct ancestor of modern Europeans, but she is a predecessor of the hunter-gathers that lived in Europe until the end of the last Ice Age."
Her DNA and that of her people have mostly been excluded from modern history. Presumably, they didn’t survive the difficult LGM / Ice Age conditions that prevailed in Europe approximately 20,000 years ago, which inevitably reduced population in the region. "This is exciting since it teaches us more about the early population history of Europe,” Jakobsson continued. “Peştera Muierii 1 has much more genetic diversity than expected for Europe at this time.
This shows that genetic variation outside of Africa was considerable until the last Ice Age, and that the Ice Age caused the decrease in diversity in humans outside of Africa." Before climate conditions became extreme and began thinning the population, it appears the descendants of those who’d left Africa tens of thousands of years earlier still retained a substantial level of genetic diversity, or at least that is what this new genetic study concludes.
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Contrary to previous belief, the African ancestors of the Eurasians may have been quite diverse from the beginning. Or they may have left in waves rather than all at once, with each successive wave adding some new genetic variations to the collective DNA pool. Before the climate deteriorated, various groups of European hunter-gatherers may have been more in contact with each other, allowing for interbreeding that would promote greater genetic diversity.
The skull of Peştera Muierii 1, whose entire genome has been sequenced as part of the genetic study. ( Mattias Jakobsson / Uppsala University )
The (Partial) Return of Europe’s Lost Genetic Diversity
The collective genetic heritage of modern Europeans and their cousins living in the Americas and elsewhere is not as lacking in diversity as it used to be. After the last Ice Age ended (around 10,000 BC or so), the Agricultural Revolution dramatically transformed life on the Eurasian continent. As farming spread, populations grew, trade expanded, migratory movements increased, and people in general were no longer as isolated from each other.
Over time populations mixed, and genetic diversity began to gradually increase. It is notable, however, that even now the people of sub-Saharan Africa are more genetically diverse than modern Europeans. The Last Glacial Maximum ended 20,000 years ago, yet its imprint can still be observed today, in the genes of those whose ancient ancestors suffered through it.
Top image: The genetic study includes the entire genome sequence of a woman who lived 35,000 years ago, extracted from a skull found in Romania in the Peştera Muierii cave. Source: Mattias Jakobsson / Uppsala University
By Nathan Falde