[Giant family trees based on ancient DNA from thousands of people
are revealing prehistoric politics and social structure]
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SUNDAY SCIENCE: FAMILY TIES  
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Andrew Curry
October 5, 2023
Science
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_ Giant family trees based on ancient DNA from thousands of people
are revealing prehistoric politics and social structure _

Bronze Age people buried men and women in pairs beneath the floors
and inside the walls of the hilltop fortress of La Almoloya, near
modern-day Murcia, Spain., PROYECTO BASTIDA/AUTONOMOUS UNIVERSITY OF
BARCELONA

 

The burial jar, found under the floor of a mountaintop citadel called
La Almoloya in southeastern Spain, held a puzzle. Almost 1 meter in
diameter, the vessel entombed a woman in her late 20s with a shining
silver diadem on her forehead. She also had silver earplugs threaded
through with silver hoops, an awl covered in silver—and a companion:
a middle-age man laid to rest in the same jar with a fraction of her
wealth. The pair were likely prominent members of a Bronze Age
protostate called El Argar, which dominated much of the Iberian
Peninsula from hilltop strongholds for nearly 700 years, beginning
around 2200 B.C.E.

When archaeologists first excavated these tombs more than a century
ago and found many women and men buried together in large jars, they
assumed the pairs were royal couples. But given the wealth gap between
women and men, later researchers concluded the jars held relatives who
died years apart. They thought the women’s rich adornments suggested
a matriarchy, where powerful women were buried and their sons or
grandsons added to their tombs later.

Then, in 2019, a team of geneticists and archaeologists extracted DNA
from the La Almoloya woman and her companion, along with 66 other
people buried in pairs and singly in the walls and under floors of the
hilltop houses. Rather than ancestors and descendants, the analysis
showed, the couples were partners. In three cases, children were
buried near their parents, who were buried together; one baby girl was
the daughter of the woman and man buried in the palace. “We did not
expect that,” says co-author Roberto Risch, an archaeologist at the
Autonomous University of Barcelona. “But [the couples] must have
been contemporary, because they had offspring together.”

DNA revealed the puzzling connection between a woman and man buried
together in a jar at La Almoloya, a Bronze Age fortress in Spain.
AUTONOMOUS UNIVERSITY OF BARCELONA

The results also revealed that the elite women seemed to be
transplants, perhaps from other high-status hilltop settlements.
Unrelated to others buried at the site, the women married men who were
related to each other and apparently local, perhaps as a way to knit
far-flung El Argar settlements into a cohesive early state.
“Probably women were crucial in social networking,” Risch says.
“It’s clear the culture’s protagonists are women.”

The results from La Almoloya, published last year, are part of a surge
of new studies that are shifting the focus of ancient DNA research
from genetic links between populations toward intimate, interpersonal
connections. As the cost of DNA sequencing has plummeted, researchers
have started to sequence genomes from many people at a site, revealing
the structure of ancient communities. “It’s gotten so cheap that
you can do whole cemeteries,” says computational biologist Harald
Ringbauer of the Max Planck Institute for Evolutionary Anthropology
(EVA). Combined with more traditional archaeological data, this
tsunami of ancient DNA promises unprecedented insights into
prehistoric family practices, group identity, and power. “We can
infer not only biological kinship, but social practices,” says
geneticist Vanessa Villalba-Mouco of EVA. “We can understand
marriages, maybe, in the past.”

Already, geneticists and archaeologists have teamed up to dissect the
marriage patterns of Bronze Age steppe nomads and traced thousands of
living descendants of enslaved women buried 200 years ago in a
forgotten Maryland cemetery. Forthcoming ancient family trees,
presented at two recent conferences and as preprints, promise to
reveal not just siblings and parent-child relationships, but distant
cousins 10 degrees removed, such as at an Iron Age English site where
the burials of 170 relatives spanning 10 generations are grouped by
maternal ancestry. At the International Society for Biomolecular
Archaeology meeting last month, researchers reported tracing kinship
ties among hundreds of people from a remote Polynesian island, showing
that millennia-old social practices on the island shifted along with
new arrivals.

“There’s extraordinarily exciting stuff happening, and it’s not
just geneticists who are excited about it,” says Australia National
University archaeologist Catherine Frieman. “We’re finally at a
point where you can actually ask archaeological questions about this
data,” like how people in the past organized societies and venerated
ancestors.

The field “is really blooming,” agrees Zuzana Hofmanová, an EVA
geneticist who is working on reconstructing the social structure of
medieval Moravia using the bones of people buried under Czech and
Slovak churches. “We’re just scratching the surface. There’s a
lot to be done, and it’s really fun.”

AFTER THE FIRST COMPLETE ancient human genome was published in 2010,
demonstrating the power of ancient DNA technology, a wave of studies
mapped ancient migrations and population shifts. The work drew on
samples widely scattered in time and space, because sequencing ancient
genomes was at first so expensive that researchers often sampled just
one or two individuals per site. Geneticists focused on broad patterns
of similarity in the DNA, and archaeologists seeking fine-grained
analyses of social structure and culture were sometimes sidelined.
“We told stories from a biological perspective that were only
indirectly related to actual history,” says Joachim Burger, a
geneticist at Johannes Gutenberg University Mainz. “Archaeologists
always hated us for that, and they’re absolutely right.”

Today, sequencing can be done at a fraction of what it cost a decade
ago, and often yields more information per sample. Researchers can
analyze well-preserved DNA from an ear bone for as little as a few
hundred dollars—about the same price as getting a radiocarbon date.
Based on shared stretches of DNA, studies can identify siblings and
link grandparents to grandchildren, tracing the chronology of a
cemetery in a way traditional radiocarbon dating, accurate to several
decades at most, cannot. “We often tell archaeologists to wait and
do radiocarbon dating after we put together the pedigree,” says
University of the Basque Country geneticist Iñigo Olalde.

In the early days of ancient DNA, such kinship information was
considered noise. As a Ph.D. student in 2015, Olalde recalls working
out a way to identify first-degree relationships among ancient
individuals—in order to weed siblings and parents out of his data
sets. “If you want to understand how people move, you want as many
unrelated individuals as possible. A family is just the same DNA all
over again,” Olalde says. “We weren’t particularly interested in
families.”

He was surprised to find archaeologists felt differently. As ancient
DNA technology improved, “we realized there was a lot of potential
… it wasn’t just father-son, or a couple of siblings,” he says.
“It was whole families, over multiple generations.” Soon, he was
partnering with archaeologists to spin samples originally gathered for
sprawling population studies into papers focused on prehistoric
kinship.

IN THE LATE 1970S, dozens of skeletons were found under a
50-meter-long barrow called Hazleton North, built 5700 years ago by
some of the earliest farmers in Great Britain—part of the same
population that began to construct Stonehenge 700 years later. For
decades, archaeologists wondered whether Hazleton and similar mounds
were like family crypts or functioned more as shared shrines,
collecting biologically unrelated members of the community.

A reconstruction of the 5700-year-old Hazleton North barrow in
England, in which dozens of family members were buried over
generations.CORINIUM MUSEUM © COTSWOLD DISTRICT COUNCIL

DNA from the tomb has now provided clear answers: Hazleton was a
family affair. Working with a team that included Newcastle University
archaeologist Chris Fowler, Olalde showed the tomb contained 27
relatives spanning five generations, as well as seven unrelated
people. Fifteen of the men in the tomb were related by descent to a
single man, whereas none of the adult women were. Although the family
tree included two young girls, adult women descended from the founder
were conspicuously missing (see graphic
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below).

That suggests that among these Neolithic Britons, women were buried
with the family of their mates, not their parents—an echo of
arrangements in the later El Argar culture that opens the possibility
that the people at Hazleton were patrilocal, too. “In the absence of
genetics, we just couldn’t tell,” Fowler says. Now, “We can
combine biological sex with what we know about age to see that
socially this was something significant.” Archaeologists had
speculated about patrilocality in past societies based on ethnographic
evidence and clues from bone chemistry, but had never been able to
conclusively demonstrate it. Fowler hopes studies of isotopes in the
bones, which can serve as a geographic fingergprint, can show how
those men and women moved during their lifetimes.

Even though the women at Hazleton were unrelated, they apparently
helped structure the extended families. The family’s founding father
had four female partners. They were apparently from different
generations, because a later woman in the tomb had children with the
founder’s son as well as his grandson by a different partner,
suggesting the son and grandson were somewhat similar in age. So the
team guesses the founder’s four unions were sequential, spread over
his lifetime.

Over the course of a century or more, burials were organized according
to the female line. Two women and their descendants were buried in the
tomb’s southern chamber, whereas offspring of the other women were
buried in a separate passage on the other side of the mound. “When
you look at the layout … it seems to really matter which of those
first generation women you were related to, and it seems to have been
followed for five generations,” Fowler says. “That male lineage
unifies the tomb, whereas female ancestors subdivide the community.”

A Neolithic family affair

The complex family tree of a Neolithic clan buried in a chambered tomb
called Hazleton North shows the promise of DNA to reveal ancient
relationships. The founder was one male; shades of blue indicate his
descendants with each of four female partners. The tomb holds many of
his male descendants, along with their young children of both sexes
(smaller symbols). Adult daughters are missing, presumably buried
elsewhere. One third generation male descended from the founder on
both sides.

D. AN-PHAM/SCIENCE

This summer, the longest and largest pedigree yet was published, from
a Neolithic site in France called Gurgy ‘les Noisats,’ where
nearly 100 individuals have been sequenced. The site predates Hazleton
by 1000 years, and it provides strong evidence for patrilocality:
Dozens of people over seven generations traced their descent back to
one man. To date, most of the dozen or so prehistoric family trees
from Neolithic and Bronze Age Europe suggest patrilocality. “It’s
surprising how consistent it’s been,” given the variety of social
structures seen in recent societies, says Ian Armit, an archaeologist
at the University of York who wasn’t part of the Gurgy team.

Others caution that a handful of studies from a 5000-year period
across Europe isn’t enough to show patrilocality was a rule.
“We’re still looking at single-site studies that don’t allow us
to draw strong conclusions,” says Wolfgang Haak, a geneticist at
EVA.

Some DNA from Gurgy posed riddles. There were no half-siblings,
strange at a time when people died early and partners could have taken
another mate. The absence suggests an avoidance of even serial
partners, says Ghent University geneticist Maïté Rivollat. “Maybe
they had rules we don’t know about in terms of who was buried there,
or maybe they were strictly monogamous.”

At Gurgy, the team also did a new kind of analysis, adapting a
technique commonly used by commercial ancestry testing companies to
identify distant cousins. Called “identical by descent,” or IBD,
analysis, it compares the frequency and length of identical stretches
of DNA to find more distant relatives. Standard ancient DNA analysis
can connect people two degrees apart at most—a grandmother to her
grandson, for example. IBD analysis allows geneticists to trace
distant cousins, great-great-grandparents, or beyond.

IBD analysis showed how women influenced Gurgy’s patrilocal
community. “We see one woman leaves the community and a couple of
generations later her descendants come back in,” Ringbauer says. For
example, a woman who had no daughter buried in the cemetery did have
maternal descendants buried there. The missing female relatives must
have left and borne offspring elsewhere; those offspring’s
descendants later returned and were buried at Gurgy. That suggests
women stayed connected to their home village or birth family as part
of a larger regional network.

Researchers are beginning to apply IBD to other sites and time
periods. In a recent preprint, for example, Ringbauer identified
second cousins who were buried 5000 years ago—and 1400 kilometers
apart—in southern Russia and central Mongolia. Both men were members
of the Afanasievo culture, an eastern variant of the steppe Yamnaya
people who made a major genetic contribution to European populations
around that time. At least one of the cousins must have traveled
hundreds of kilometers across the steppe during his life, an early
example of dramatic mobility in the space of a few generations.

As ancient DNA databases grow exponentially, Ringbauer hopes access to
tens of thousands of published genomes will create a sort of 23andMe
for the distant past, linking prehistoric people to one another across
time and space. “We can now screen tens of thousands of ancient
individuals for IBD,” Ringbauer says. “My vision is you’d add a
study and immediately see, ‘Oh, there’s a second cousin over
there.’”

PERHAPS CHASTENED by past criticisms, geneticists are now quick to
concede that biological relatedness is only one element of kinship.
Ethnographic studies of recent societies are rich in examples of
biological parentage taking a back seat to other kinds of family
relationships. They include matrilineal systems in which the most
significant male relative is the mother’s brother and communities
where fatherhood is determined by the transfer of cattle to a
woman’s family. “Kinship is not just genetically determined,
it’s socially constructed,” says Joanna Bruck, a University
College Dublin archaeologist. “There has to be an acknowledgement
that genetics can be read in multiple ways.”

Archaeology can help guide those readings, as an early study of
biological relatedness showed. It scrutinized the genomes of 84 people
buried in small cemeteries up and down Germany’s narrow, fertile
Lech Valley between 2500 B.C.E. and 1650 B.C.E., during the
technological transition from Neolithic farming to the Bronze Age.
Published in 2017, the results showed patrilocality. But many Lech
Valley cemeteries included both biologically related individuals and
those with no genetic links to others in the graveyard.

Material culture helped explain the pattern. The unrelated people had
many fewer grave goods, says Alissa Mittnik, a geneticist at EVA who
co-authored the study. “The farmsteads were probably run by families
who accumulated wealth. The others might have been farm workers,
servants, or enslaved people.” Those people did not establish
families in one place across generations, but were buried in the plots
of the presumably wealthier landowners, who did.

To puzzle out such community relationships, geneticists and
archaeologists are forging stronger ties. For example, when Ludwig
Maximilian University of Munich archaeologist Philipp Stockhammer, a
lead author on the Lech Valley paper, was awarded a European Research
Council grant to look for kinship patterns in Bronze Age Greece and
the Aegean, his first step was to reach out to Greek archaeologists,
asking for sites and questions where DNA could contribute. “Kinship
analysis forces every lab to work closer with local archaeologists,”
Stockhammer says. “You can’t do without archaeologists anymore.”

Earlier this year, Stockhammer’s team found that one-third of its
samples from another Aegean project had long stretches of shared DNA,
indicating they were the offspring of first cousins. That rate of
close-kin interbreeding is highest documented anywhere in the past,
although some modern societies have similarly high levels of cousin
marriage.

Although the practice was slightly more frequent on isolated islands,
it was seen across the Aegean, suggesting it was the result of a
social practice or choice, rather than a lack of potential partners.

“Why do you have long-distance mobility of marriage partners in
Central Europe in the Bronze Age, but not in Greece?” Stockhammer
asks. Culture may hold an answer: The Bronze Age people of the Aegean
grew olives and grapes. Those crops take decades to establish,
offering an incentive to keep land in the family. “This kind of data
lets us see how certain practices compare across regions,”
Stockhammer says. “The future of archaeogenetics is going to be
zooming in, and then zooming out.”

Paleogeneticists also hope to broaden their work beyond Europe, where
research has flourished thanks to adequate funding, access to samples,
and good preservation in the continent’s relatively cool caves and
burials. (See a review of research outside of Europe
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could also inform modern medicine, if researchers can identify a
genetically inherited disease and trace it back generations.
“Pedigree studies on modern individuals have been useful in tracing
rare variants and how they’re inherited,” Hofmanová says. “Nine
generation pedigrees from the past—and soon longer—will enable you
to trace rare variants much further than we can in modern
individuals.”

In 2008, Haak was one of the first to apply ancient DNA to identify
parents and children in a central German grave. Fifteen years later,
the scope of information that DNA can reveal about life in the past is
rapidly widening. “The question when you approach every grave is:
Who are they? Are they related? Does proximity in space mean
kinship?” Haak says. “Getting closer to answering some of those
questions is a long-held dream that came true.”

_ANDREW CURRY is an award-winning journalist with more than 20 years
of experience reporting from five continents covering science, travel,
history, politics, cycling and more. He has for a wide variety of
publications, from Architect and Bicycling to National Geographic, The
New York Times, Rouleur, and Wired. I am a contributing correspondent
for Science [[link removed]] and a contributing editor at
Archaeology [[link removed]]. Andrew Curry lives in
Berlin, Germany._

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_In the quest to measure how antimatter falls, the possibility that it
fell "up" provided hope for warp drive. Here's how it all fell apart._
ETHAN SIEGEL
Starts with a Bang  October 3, 2023

* Science
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* Archaeology
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* marriage
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* human genome
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* neolithic
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* kinship
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