Scientists once could reconstruct humanity’s distant past only from the mute testimony of ancient settlements, bones, and artifacts.
No longer. Now there’s a powerful new approach for illuminating the world before the dawn of written history – reading the actual genetic code of our ancient ancestors. Two papers published in the journal Nature more than double the number of ancient humans whose DNA has been analyzed and published – to 1,336 individuals. In 2014, the number was just 10.
The new flood of genetic information represents a “coming of age” for the nascent field of ancient DNA, says lead author David Reich, a Howard Hughes Medical Institute investigator at Harvard Medical School – and it upends cherished archeological orthodoxy. “When we look at the data, we see surprises again and again and again,” says Reich.
Together with his lab's previous work and that of other pioneers of ancient DNA, the Big Picture message is that our prehistoric ancestors were not nearly as homebound as once thought. “There was a view that migration is a very rare process in human evolution,” Reich explains. Not so, says the ancient DNA. Actually, Reich says, “the orthodoxy – the assumption that present-day people are directly descended from the people who always lived in that same area – is wrong almost everywhere.”
Stonehenge’s Builders Largely Vanish
In one of the new papers, Reich and a cast of dozens of collaborators chart the spread of an ancient culture known by its stylized bell-shaped pots, the so-called Bell Beaker phenomenon. This culture first spread between Iberia and central Europe beginning about 4,700 years ago. By analyzing DNA from several hundred samples of human bones, Reich’s team shows that only the ideas – not the people who originated them – made the move initially. That’s because the genes of the Iberian population remain distinct from those of the central Europeans who adopted the characteristic pots and other artifacts.
But the story changes when the Bell Beaker culture expanded to Britain after 4,500 years ago. Then, it was brought by migrants who almost completely supplanted the island’s existing inhabitants – the mysterious people who had built Stonehenge – within a few hundred years. “There was a sudden change in the population of Britain,” says Reich. “It was an almost complete replacement.”
For archeologists, these and other findings from the study of ancient DNA are “absolutely sort of mind-blowing,” says study coauthor Barry Cunliffe, an archaeologist and professor emeritus at the University of Oxford. “They are going to upset people, but that is part of the excitement of it.”
Vast Migration from the Steppe
Consider the unexpected movement of people who originally lived on the steppes of Central Asia, north of the Black and Caspian seas. About 5,300 years ago, the local hunter-gatherer cultures were replaced in many places by nomadic herders, dubbed the Yamnaya, who were able to expand rapidly by exploiting horses and the new invention of the cart, and who left behind big, rich burial sites.
Archeologists have long known that some of the technologies used by the Yamnaya later spread to Europe. But the startling revelation from the ancient DNA was that the people moved, too – all the way to the Atlantic coast of Europe in the west to Mongolia in the east and India in the south. This vast migration helps explain the spread of Indo-European languages. And it significantly replaced the local hunter-gatherer genes across Europe with the indelible stamp of steppe DNA, as happened in Britain with the migration of the Bell Beaker people to the island.
“This whole phenomenon of the steppe expansion is an amazing example of what ancient DNA can show,” says Reich. And, adds Cunliffe, “no one, not even archeologists in their wildest dreams, had expected such a high steppe genetic content in the populations of northern Europe in the third millennium B.C.”
These scientific leaps forward have been fueled by three key developments. One is the dramatic cost reduction (and speed increase) in gene sequencing made possible by advanced machines from Illumina and other companies. The second is a discovery spearheaded by Ron Pinhasi, an archaeologist at University College Dublin. His group showed that the petrous bone, containing the tiny inner ear, harbors 100 times more DNA than other ancient human remains, offering a huge increase in the amount of genetic material available for analysis. The third is a method implemented by Reich for reading the genetic codes of 1.2 million carefully chosen variable parts of DNA (known as single nucleotide polymorphisms), rather than having to sequence entire genomes. That speeds the analysis and reduces its cost even further.
The new field made a splash when Svante Pääbo of the Max Planck Institute for Evolutionary Anthropology, working with Reich and many other colleagues, used ancient DNA to prove that Neanderthals and humans interbred. Since then, the number of ancient humans whose DNA Reich has analyzed has risen exponentially. His lab has generated about three-quarters of the world’s published data and, including unpublished data, has now reached 3,700 genomes. “Every time we jump an order of magnitude in the number of individuals, we can answer questions that we couldn’t even have asked before,” says Reich.
Ancient DNA offers the promise of studying not only the movements of our distant ancestors, but also the evolution of traits and susceptibilities to diseases. “This is a new scientific instrument that, like the microscope when it was invented in the seventeenth century, makes it possible to study aspects of biology that simply were not possible to examine before,” explains Reich.
Moreover, its potential impact extends beyond the scientific details to the larger question of what it means to be human. The fact that humanity’s past is rife with huge migrations and extensive genetic mixing puts the scientific kibosh on the claims from any group of racial purity or genetic superiority. Or in Reich’s opinion, “the overwhelming effect of this field has been to explode stereotypes and reduce prejudice."
This article has been republished from materials provided by the Howard Hughes Medical Institute. Note: material may have been edited for length and content. For further information, please contact the cited source.
References: Olalde, I., Brace, S., Allentoft, M. E., Armit, I., Kristiansen, K., Booth, T., … Reich, D. (2018). The Beaker phenomenon and the genomic transformation of northwest Europe. Nature. https://doi.org/10.1038/nature25738