The Genetic History of Prehistoric Britain

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Dr Tom Booth, Natural History Museum - September 2017 Recent Lecture

In investigating the past we are going through another revolution like the radio carbon revolution:  looking at ancient DNA, a powerful tool.  A current project involves extracting DNA from British skeletons from 10,000 years ago to the present day, and detecting changes through time.  Initially there were some false conclusions: a lot of results obtained were actually the result of modern contamination, such as a connection apparently found between Cheddar Man and local residents, suggesting a population living there for thousands of years.  It has been difficult to separate samples from modern contamination due to handling etc., but with new methods contamination is not now such a problem.  Although DNA degrades through time, the “damage profile” can be assessed, allowing authentication of genuine ancient DNA.  Small sequences of DNA can provide Gigabytes of data, information from across the person’s entire genome.  

In the last few years labs in the USA and Denmark have been processing ancient DNA material from across Europe, providing more information about the genetic history of populations, so we can now construct a narrative covering some 40,000 years.   We have to understand what happened in Europe to understand what happened in Britain;  till 8000 years ago Britain was attached to Europe anyway.   

Before the last icesheet melted, people (e.g. the Aurignacians) had spread across Europe: 
26,000 years ago: the genetic signal of people changed: different people moved into Europe.  The   Aurignacians moved down into Spain.
24,000 years ago: we were in the last glacial maximum, with no-one in Europe except in refugia in Southern Europe.  Then the ice retreated and people migrated northward – including the late glacial Magdalenian culture.
14,000 years ago: another change in the DNA, another population change: other people, probably from the Near East, replaced those in Europe –with the warmer climate they were spreading into Europe and Britain.
From 10,000 years ago: in the Mesolithic period, nomadic hunter-gatherers were living in Europe following the game.

Then came another genetic change which spread across Europe: the arrival of farming (invented in the Near East 10,000 years ago) - the Neolithic:  cultivated plants and animals arriving.  Now there was a larger population size.  Farming people spread from the Near East into Europe, then split into two genetically distinct lines:  one migrated through the Mediterranean area to Iberia, another, the LBK culture, into Central Europe;

They were interbreeding with the hunter-gatherers, who were being integrated into farming, with at first a disproportionate ratio: a lot of Neolithic, a few hunter-gatherers, but as the farmers moved West, interbreeding again and again, the ancestry is still mostly Near Eastern but more hunter-gatherers enter the genome.  
2,700-2,500BC in Northern Europe: another genetic change, associated with the Yamnaya Culture from near the Caspian Sea.  Yamnaya DNA becomes visible in Europeans, suggesting interbreeding with the local Neolithic populations.  Why did the Yamnaya suddenly move out in all directions?  Evidence of Pestis suggests the Yamnaya may have been carrying plague.  Were they starting epidemics, reducing and replacing local populations, who would have had no resistance?  This does not seem like invasion, more a change in lifestyle.  Yamnaya DNA also spreads eastward into Northern India.  Were these people the first to ride horses and have wheeled vehicles?  Were they the origin of the Indo-European languages?  They changed local cultures – perhaps started the European Corded Ware Culture.

So, current European ancestry is threefold - Steppe/hunter-gatherer/farming.  Modern European countries have different percentages of these three ancestries, with a lot more evidence of Steppe in Northern European countries such as Norway, less in Southern European, e.g. Sardinia.  

Our genes can also denote physical characteristics such as skin and eye colour.  It has always been assumed people moving into Europe developed pale skin in order to absorb UV radiation to make Vitamin D.  But the genes suggest ancestral dark skin persists till the European Neolithic, and was the predominant skin colour up to 4,500 years ago, implying the Palaeolithics and Mesolithics had dark skin.  Pale skin is relatively recent, perhaps spread by the migration from the Asian Steppes where pale skin had developed.  Blue eyes had come thousands of years earlier.   So ideas about these two  characteristics going together is modern thinking.  The DNA of British Neolithics is closer to the Iberian people, suggesting physical migration Northward from Western Europe, something also suggested by the spread of megalithic tombs from Iberia, up the French coast, then into Britain.  

After the Yamnaya migration and Corded-ware Culture came the Beaker period, the earliest evidence of which occurs in Southern Iberia, but there is no Steppe ancestry there.  So Beaker Culture spread across Europe from Iberia as an idea, perhaps through the old trade routes, arriving in Britain apparently direct from the Netherlands. 

Beaker Culture is mostly defined by beakers in graves with an individual burial.  Before this, funerary practice in Britain was in the form of cremations; after 2,500BC, a lot of individual burials, but still some cremations: perhaps some lingering Neolithics.  Perhaps there was also a religious change.  In the British late Neolithic, the economy had started to fail.  People were travelling from all over Britain to build monuments, but already before the Beaker Culture arrived, cereal production and population had declined, perhaps due to a downturn in climate around 5000 years ago, and there was a switch from mixed farming to nomadic pastoralism.  So populations were so low, perhaps the Beaker people filled up the spaces?   There are no signs of invasion – no mass graves.  Were Beaker people better fitted for survival and outcompeted?  Whether their culture spread as a result of people (antiquarians had pointed out the different skull shape of Beaker people) or ideas migrating was one of the questions addressed by DNA analysis of skeletons from this period from all over Europe.  In Britain, Steppe ancestry was brought in by the Beaker culture - earlier than 2,500 years BC, no Steppe ancestry, afterward, quite a lot.  Beakers also seem to coincide with the first appearance of metal working, first copper, later bronze.

This work can also show the process of natural selection, e.g. when at the start of farming people started living in settlements with animals, and were therefore exposed to a greater variety of diseases: their DNA adapted to this, creating resistance to disease.  We are the only animal which drinks the milk of other animals, and a change in genes reveals a new ability to digest cow’s milk; fermenting of milk gets rid of the lactose so it can be drunk by those who are lactose intolerant.  Beakers from burials often seem to have contained fermented milk.  

By the British Middle Bronze Age there is hardly any Neolithic ancestry left but a lot of Beaker ancestry, suggesting an over 90% replacement of Neolithics by Beaker people.  Neolithic ancestry has never returned - it is not in modern people.  So nobody in modern Britain is descended from those who built Stonehenge.  So heritage cannot be based on ancestry. 
2,500BC: in Britain came a Chalcolithic period (stone and copper); 2,200BC: bronze.  Towards the Iron Age, in England and Wales there is slight increase in ancestry from Iberia/Northern France: is this the Celts?  This is still speculative.

Yvonne Masson