Ancient Britons 'replaced' by newcomers

http://www.bbc.com/news/science-environment-43115485

Ancient Britons 'replaced' by newcomers

By Paul Rincon
Science editor, BBC News website

21 February 2018

The ancient population of Britain was almost completely replaced by newcomers about 4,500 years ago, a study shows. The findings mean modern Britons trace just a small fraction of their ancestry to the people who built Stonehenge. The astonishing result comes from analysis of DNA extracted from 400 ancient remains across Europe. The mammoth study, published in Nature, suggests the newcomers, known as Beaker people, replaced 90% of the British gene pool in a few hundred years. (snip) The reasons remain unclear, but climate change, disease and ecological disaster could all have played a role.

People in Britain lived by hunting and gathering until agriculture was introduced from continental Europe about 6,000 years ago. These Neolithic farmers, who traced their origins to Anatolia (modern Turkey) built giant stone (or "megalithic&quot structures such as Stonehenge in Wiltshire, huge Earth mounds and sophisticated settlements such as Skara Brae in the Orkneys.

But towards the end of the Neolithic, about 4,450 years ago, a new way of life spread to Britain from Europe. People began burying their dead with stylised bell-shaped pots, copper daggers, arrowheads, stone wrist guards and distinctive perforated buttons. Co-author Dr Carles Lalueza-Fox, from the Institute of Evolutionary Biology (IBE) in Barcelona, Spain, said the Beaker traditions probably started "as a kind of fashion" in Iberia after 5,000 years ago. From here, the culture spread very fast by word of mouth to Central Europe. After it was adopted by people in Central Europe, it exploded in every direction - but through the movement of people.
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The genetic data, from hundreds of ancient British genomes, reveals that the Beakers were a distinct population from the Neolithic British. After their arrival on the island, Beaker genes appear to swamp those of the native farmers.
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The newcomers brought ancestry from nomadic groups originating on the Pontic Steppe, a grassland region extending from Ukraine to Kazakhstan. These nomads moved west during the Neolithic, mixing heavily with established populations in Europe. The Beaker migration marks the first time this eastern genetic signature appears in Britain.
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What triggered the massive genetic shift remains unclear. But a paper published in PNAS journal last year suggested a downturn in the climate around 5,500 years ago (3,500 BC) pushed Neolithic populations into a thousand-year-long decline. Dr Steven Shennan, from UCL, who co-authored that study, told BBC News: "In Britain, after a population peak at around 3,500 or 3,600 BC, the population goes down steadily and it stays at a pretty low level until about 2,500 BC and then starts going up again. Around 2,500 BC the population is very low and that's precisely when the Beaker population seems to come in."

The reasons behind this slow population decline were probably complex, but the temporary downturn in the climate caused a permanent change in the way people farmed. One possibility is that the over-exploitation of land by Neolithic farmers applied pressure to food production.
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