DNA technology enables scientists to discover more than ever about human ancestry from archaeological finds.
Research released in the journal Nature Communications has explained how remains of an ancient tribe discovered in the Caucasus is in fact a newly discovered fourth group of early humans that contributed to the European gene pool.
Fossilised remains of two later members of this new group, discovered in a cold, dry cave in Georgia, enabled researchers to isolate and sequence their DNA.
Previously, scientists had identified three migrations of early humans from what we now call Africa, across the modern day Middle East and into Europe. One group spread across Turkey, mainland Europe and into Spain. Another settled in the Levant in the Middle East, before migrating into the Europe and a third moved into Western Europe from southern Russia, possibly, according to DNA analysis, to escape a plague epidemic. The newly discovered group is thought to have split from other groups of early humans by travelling north into the Caucasus.
The researchers compared their findings with other fossil genomes found around Europe and the Middle East, and discovered that these Caucasus hunter-gatherers diverged from western hunter-gatherers shortly after humans began expanding into Europe 45,000 years ago.
Their DNA also showed a continued mixture with those living in the Levant area until around 25,000 years ago when their gene pool appears to have shrunk considerably. This suggests the group were isolated in the mountains for around 15,000 years, probably during the last Ice Age.
Professor Daniel Bradley, who helped to lead the research at Trinity College Dublin, explains that for the past thirty or forty years scientists have tried to build up a picture of what happened in the past, and of ancient genetics, using modern DNA methods.
“The models crumble, though, when you decode a full genome from the past,” he says.
Professor Bradley says that to understand what happened in the past it’s vital that scientists actually sequence past genomes.
“There have been so many major events in human history. In Europe alone there was a mass Bronze Age migration, another migration of Neolithic farmers,” he says. “Before using modern data we could speculate about this, but couldn’t say for sure.”
Over the last year, scientists have discovered that some Irish people are descended from Middle Eastern Stone Age farmers. Also that white skin evolved in Europeans 8,000 years ago and Basques are related to Iberian farmers from 3,500 to 5000 years ago. Fossilised remains discovered in a South African cave turned out to be a previously undiscovered human ancestor, since dubbed Homo Nadeli.
“Archaeologists can imagine what might have happened in the past,” Prof Bradley says, “but now, through analysing ancient human DNA, we can tell for sure whether migration happened or not, in specific areas.”
The genome is the genetic blueprint for a human, contained within the nucleus of every cell. Scientists at Trinity College Dublin, involved in the Irish ancestry project, used a technique called whole-genome analysis to read, not the unique characteristics of each individual, but a wider history of ancestral migration and settlement in the DNA from the remains they analysed.
“Recent advances in sequencing techniques in medical science enable us to sample entire genomes in a few days,” Prof Bradley says. “Ten years ago we were drawing conclusions after sampling a few thousand base pairs.
“There are multiple factors that determine whether DNA is preserved in ancient specimens, not all of them understood. Time, temperature, soil chemistry, density of the bone fragment – the denser the more likely DNA will be preserved.”
Technology and archaeology
Technology is now part of an archaeologist’s everyday life. Gone are the days when an amateur enthusiast dug up a few ancient pots and looked in a book, almost as old as the pots themselves, to find out what they were and where they came from.
Ian Freestone, professor of archaeological materials and technology at University College London (UCL) says that technology is vital for archaeologists as much of what they learn about the past depends on how well they can investigate sites and materials.
“To do this well, you need advances in a whole range of technologies,” he says.
CAT scans enable scientists to see inside a mummy sarcophagus without removing the bandages, high powered X-ray beams restore a 200 year old opera score, 3D imaging reveals what the Ancient Greeks wrote on their stone tablets. LIDAR helps archaeologists find ancient features that can barely be seen by the human eye. That could be ancient hill forts in Yorkshire, 18th Century farms covered by forests in New England, USA, even an 11,000 year old settlement underneath the Baltic Sea.
LIDAR also detects buried features that have caused changes in vegetation and soil moisture. For example, E&T has reported on how researchers used motorised magnetometers, ground-penetrating radar arrays and electromagnetic induction sensors to investigate Stonehenge and it surroundings.
And now these technologies are being taught to university students looking to unearth further ancient secrets.
“Undergraduates at UCL will do some lab work – I’ve got groups doing geophysics and electron microscopy at the moment” Freestone says. “These courses are designed to give students a good grounding in the range of scientific and humanities skills they’ll need to become field archaeologists. For those who want to go on and specialise in a more technological area of archaeology, we also run a range of master’s degrees,” he adds.