An ancient DNA study of dozens of skeletons found in a monumental Neolithic tomb in Britain has allowed researchers to reconstruct to an unprecedented degree the family tree of a prehistoric clan that lived on the island some 5,700 years ago.
It has also revealed some fascinating cultural mores of these Neolithic farmers, such as the fact that they placed great importance on both paternal and maternal descent, that they seemingly adopted non-biological children, and had multiple husbands and wives.
The analysis published Wednesday in Nature sequenced the genome of 35 individuals representing five generations of people who were buried at Hazleton North, a massive 50-meter-long stone cairn in the picturesque Cotswold area, west of Oxford. Among those buried there, 27 people were closely related, representing by far the largest family pedigree reconstructed through ancient DNA, according to the team of archaeologists and geneticists that conducted the study.
Hazleton North was excavated between 1979-1982 and is one of more than 100 Neolithic funerary monuments that dot the area between south Wales and southwestern England, and are known as the Cotswold-Severn long barrows. Based on radiocarbon dating, it is estimated that this cairn was in use for some 70 years, from around 3690 B.C.E. to 3620 B.C.E., the Nature study says.
Built with flat stones, most of the monument was filled in with soil, except for two chambered passageways, on the northern and southern sides of the tomb, which is where the dead were placed.
In addition to the 27 family members found there, the tomb hosted eight people who were not biological kin of the clan, and we’ll talk about who they may be later on. We will also address the mystery of why the burial contained 26 men and only nine women.
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By looking at the percentage of genetic material each individual shared with the others, the researchers were able to reconstruct the biological relationship (if there was any) between clan members and fill in the family tree, even intuiting the existence of people whose DNA they didn’t directly sample.
The founders of this dynasty appear to have been a man who fathered multiple children with at least four women. The scientists, as they tend to do, call this person by a number, but for the purposes of this article we are going to call him Jacob, like the biblical patriarch who also had four wives. We don’t know much about this Neolithic Jacob, because only a single tooth belonging to him has been recovered. But we can be sure that he was fruitful and multiplied, siring at least seven children who were male. We say “at least” because it is statistically unlikely that there wouldn’t be any daughters born unto Jacob, notes Inigo Olalde, a geneticist from the University of the Basque Country who led the genetic analysis.
This is a pattern that is repeated across the five generations present in the tomb: the few females who are found are either unrelated women who reproduced with the males of Jacob’s lineage or they are girls who died before puberty.
This suggests that this population practiced female exogamy, a custom in which, to avoid inbreeding, local men reproduce only with women from a different group, Olalde says. It is possible that some of Jacob’s missing female descendants may have been married off into a different community and ultimately buried in one of the many other long barrows in the region, notes Chris Fowler, an archaeologist from Newcastle University who is the lead author on the study. However, this only partially answers the question, because males vastly outnumber females in Cotswold-Severn monuments, suggesting that some people, mainly women, were either cremated or buried in simpler tombs that did not survive until today, Fowler says. Why that was the case is still a mystery.
Another open question regards the multiple partners. Some men and women in the clan procreated with different people. For example, one of Jacob’s “wives” – we shall call her Leah – had a son with another man, who was also a distant relative of the patriarch. Because of the exogamy rule, when women, who came from outside the clan, tended to have multiple partners they inevitably ended up with men who were related to each other, Olalde says. In one case with a high ewww factor (by our standards), one of Jacob’s sons reproduced with a woman who also had a child with one of the patriarch’s grandsons from a different matriarch.
If your head is spinning at this point, keep also in mind that that DNA doesn’t tell us whether these people actually practiced polygyny and polyandry or whether these were all cases of serial monogamy, says Prof. David Reich, a Harvard University geneticist and one of the world’s top experts in the study of ancient DNA.
In the name of the father
What we do know is that these step-children represent an exception to the strict rule of patrilineality that marked the identity of the clan’s members. Generally, only those who descended from the male spawn of the family’s founders were buried in the tomb, Reich notes.
“Belonging in this community is defined through the male lineage: you have to be able to trace yourself back to that founding family through a series of male links, and if you have female links you probably get buried somewhere else,” he says. “It’s like in the Bible: this guy begat this guy, who begat this guy, who begat that guy.”
But this seemingly biblical tradition was not rigidly enforced. The presence in the tomb of three step-children suggests that these individuals were adopted into the family and accepted as full members even though they were sired by non-lineage males, Reich says.
Of course, it is possible that women like Leah simply lied about the origin of their other children, Olalde notes. But ethnographic evidence from modern traditional societies as well as the large number of adoptions in the family tree indicates instead that this was likely a common and accepted practice, he says.
Some of the eight individuals in the tomb who were completely unrelated to the clan may also have been adopted, Olalde says. However, these unrelated individuals could also be spouses of lineage members who didn’t have kids, or who had only daughters who married into another community and are therefore not found in the tomb, he cautions.
Be that as it may, the study of Hazelton North is further evidence that, even in the Neolithic, kinship could be divorced from pure biological facts, Reich notes.
“There is an open question as to how much kinship is connected to biology. In some ethnographic contexts it’s not biological at all, it’s about friendship and adoption,” he says. “Here it is heavily correlated to biology, but not completely.”
Who’s your mama?
Another aspect of kinship that was clearly important to this culture was maternal descent. The researchers found that while patrilineality (by nature or adoption) determined membership in the community, bodies in the tomb were usually arranged according to their connection to Jacob’s wives. The descendants of two wives were all buried in the tomb’s southern chambers while the scions of the other two were gathered mostly in the northern chambers, meaning that the structure of the family determined the architecture of the tomb.
This suggests that these people knew who their maternal ancestors were up to four generations back, and that this sense of belonging had some deep significance, certainly in death, and probably also in life.
“In a patrilineal society it doesn’t mean that women are necessarily marginal,” says Fowler. “Now we can say it clearly mattered to people not just who their fathers were but who their mothers and grandmothers and great-grandmothers were. These were important women, whom they remembered and from whom they traced their identity.”
Altogether, the study’s finds point to a particularly complex family structure, which is not entirely unexpected for this period but which so far researchers had been unable to see, the archaeologist says.
This complexity may have been fostered by the particular historical circumstances of these prehistoric Brits. Farming was introduced to the British isles from the European mainland around 6,000 years ago, just a few centuries before long barrows like Hazleton North were built. The new settlers, distant descendants of the first Anatolian farmers who came to Europe, must have travelled by boat, probably from France, because the land bridge that once connected the continent to Britain had long since sunk under the sea.
Britain would witness later migrations, one of which occurred just around 3,000 years ago and was documented by Reich’s team in a separate study also published Wednesday in Nature. But this early Neolithic influx, 6,000 years ago, was notable in that it almost completely replaced the original hunter-gatherer population of Britain, Reich says.
While the people of Hazleton North were not immigrants like their recent ancestors, they were still benefiting from the rapid economic and demographic expansion brought about by the introduction of agriculture and animal husbandry, the geneticist says.
“What you see here is a family where there is a guy who reproduces with four women and is also adopting children that his reproductive partners had with other men,” he says. “This a strategy that can potentially grow a family quite rapidly in a context of economic plenty and opportunities.”
One question that future research will have to answer is how much this picture reflects the family lives of all Neolithic farmers in Britain and beyond, Fowler notes. While it may be possible to assume that this societal structure existed throughout the Cotswold-Severn region, this may not be true for other populations that built similar clusters of monuments elsewhere in England, Ireland and Scotland, the archaeologist says.
“Neolithic chambered tombs are in many parts of Britain,” he says. “Lots of communities were building these monuments in slightly different ways and I’m interested in why did they did it and what those differences mean.” Just like at Hazleton North the architecture and arrangement of the dead was linked to the family structures of its builders, studying the DNA of the bodies inside other tombs could unlock their family secrets as well.