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Some Stone Age people in Ireland left the bodies of their dead to decompose in a natural rocky chamber on a mountain. Genetic analysis of two of these bodies shows they had darker skin, like many people in Europe at the time, and suggests they lived in fairly large communities.

The boulder chamber was accidentally discovered in 2016 by a hillwalker exploring Bengorm mountain in north-west Ireland. Finding human bones on the floor, he called the police. The bones turned out to be thousands of years old and the site was turned over to archaeologists led by Marion Dowd at the Institute of Technology Sligo in Ireland. 鈥淚t鈥檚 a Neolithic site that has been completely undisturbed for 4500 to 5000 years,鈥� she says.

The team found a total of 4899 bone fragments, which belonged to at least eight individuals, both adults and children. However, the chamber wasn鈥檛 these people鈥檚 final resting place. Instead, people carried corpses to the chamber and left them there for up to 2 years to allow the flesh to decompose, then took away the skulls and other large bones. 鈥淲hat鈥檚 left behind are very small bones and very small fragments,鈥� says Dowd.

Such elaborate funerary practices were common in the Neolithic, the last phase of the Stone Age. By this time, the first farmers had moved into western Europe from further east. In the British Isles, they largely replaced the hunter-gatherers that had been living there for millennia.

Neolithic funeral practices often lasted years and were probably tied to religious beliefs about the afterlife, says Dowd. 鈥淭he physical disintegration of the body possibly mirrors the spiritual journey.鈥�

Lara Cassidy at Trinity College Dublin in Ireland managed to obtain DNA from two of the bones, belonging to two adult males from around 3000 BC. The pair were distantly related. 鈥淲e can鈥檛 say exactly what that relationship would have been, but it would have been about the same amount of sharing of genetic material as for second cousins,鈥� says Cassidy. 鈥淭hat tells us they鈥檙e coming from a community that鈥檚 sizeable enough that you can avoid close inbreeding.鈥�

Both Bengorm men were lactose-intolerant, meaning that as adults they couldn鈥檛 digest the lactose in milk without discomfort. Today, most people with European ancestry can digest lactose, but the trait only evolved within the past 5000 years 鈥� thousands of years after people began keeping dairy animals like cows.

Neolithic farmers probably coped by processing milk to remove most of the lactose, says Carles Lalueza-Fox at the Institute of Evolutionary Biology in Barcelona, Spain. 鈥淚f you make cheese, then you get rid of the lactose problem.鈥�

The two adult males had skin that was 鈥渋ntermediate to dark鈥�, according to the DNA analysis. We can鈥檛 be too precise, but their skin was probably in a range traditionally associated with the Middle East or Mediterranean today, says Cassidy.

This is in line with other Neolithic Europeans, she says. 鈥淭here was diversity. You鈥檙e getting a lot of variants circling at that time.鈥�

The Bengorm population may well have living ancestors in Ireland today, says Dowd. The site was used for funeral rites for at least 800 years, suggesting a long-lasting population.

We have less information about the hunter-gatherer groups that lived in the British Isles before the farmers, but a 2018 study of the 10,000-year-old 鈥淐heddar Man鈥� skeleton from the UK found evidence that he had dark skin that was significantly darker than the Bengorm men had.

Later, genetic variants linked to lighter skin tones became much more common in Europe, but we don鈥檛 know when that happened, says Cassidy, because we have little DNA from the Bronze Age and Iron Age so far.

鈥淭here is a habit of projecting current ranges in skin colour on past populations,鈥� says Cassidy. In reality,聽human skin tones have varied for 900,000 years, so our assumptions are often wrong.