Ancient DNA unearthed from a European rock shelter suggests that local herders tended goats and sheep more than 5000 years ago, but switched to primarily pigs 2000 years later – right about when the surrounding forests became much less biodiverse.
Although further research is needed, the findings hint that keeping pigs – which root the ground and are far less picky eaters than goats and sheep – might have played a role in how modern forests took shape. The discovery provides strong evidence that analysing ancient sedimentary DNA can – in addition to fossils and artefacts – help paint a picture of ancient human life and its effects on the environment, says at the University of Calgary in Canada.
Archaeologists already knew that people in central Europe started about 6000 years ago. Studies analysing pollen have shown that within the following two millennia, forests had . While scientists have long suspected that this agricultural practice influenced the biodiversity loss, they lacked the tools and evidence to prove it.
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Recently, researchers have been developing a technique for . Inspired by that technology, Walls and his colleagues took samples from up to 2.5 metres under the ground beneath a large rock overhang in a small canyon in the mountainous Bohemian Forest, in the Czech Republic. The area apparently sheltered animals and herders from wind, rain and sun over several millennia, says at the University of Copenhagen, Denmark.
Previous research teams have already extracted multiple well-preserved fossils from the shelter’s sediment layers, which represent the past 11,000 years. Walls, Winther Pedersen and their team analysed more than 400 million DNA sequences that they found in 10 layers of sediment. Some of the DNA came directly from plants and animals, and some from faeces.
The researchers found that the deepest, oldest sediments contained no animal DNA. But starting 7000 years ago, they saw DNA from goats, says team member at the University of Copenhagen. However, the quality of the DNA wasn’t good enough to tell if they were wild or domesticated.
From 6000 years ago, DNA indicates that domesticated goats were clearly in the area. Over time, sheep became more common, with cows sometimes accompanying them. Little by little, starting 4000 years ago, pigs became part of the mix as well.
By the late Bronze Age, 1000 years later, the most predominant domestic animal at the shelter was the pig. Although the DNA can’t clearly distinguish domestic pigs from wild boar, since they were so closely related at the time, what matters is that the animals appeared to be herded in enclosed areas, says Zampirolo.
That timing corresponds with a shift in woody plant DNA, the researchers say. Starting about 4000 years ago, beech and spruce – which lack nutritional value for animals – became predominant. Two millennia before that, the forest was far more diverse and contained primarily hazel, maple and a little bit of elm.
“What we’re able to see in this neat perspective from the DNA is that [previous research about biodiversity loss in early Bronze Age forests] coincides very clearly with this shift from sheep to pigs,” says Walls. “So there’s a fairly good indication that there could be a clear correlation between those, and that it’s sort of a bigger shift in the whole transformation of central European landscapes, in this nice representation of a single shelter.”
Associating pig herding with the change in the forest would be a “very reasonable interpretation”, says at the University of Georgia, who wasn’t involved in the study. “As the authors state, pigs and boars are less selective in their feeding habits and can be quite destructive. So it’s not surprising that an increase in relative abundance of pigs would impact the forest composition over time.”
The study adds a critical contribution to our understanding of how ancient humans interacted with the environment, especially as they began practising agriculture, she adds.
“The fact that they are able to align this with changes in the forest mosaic composition makes it a powerful tool for interpreting complex interrelationships between people, animals and plant communities,” says Pilaar Birch.
“This is a precedent-setting paper with exciting implications for the way we integrate genomics with archaeology in the future. I hope there are more like it in the future.”
Current Biology
