Discover 3

FROM TOP: DE AGOSTINI/C. BALOSSINI/BRIDGEMAN IMAGES; JAY SMITH; COURTESY JEREMY SEARLE

Røyrvik, one of the authors of the 2015 Nature

study, took the unusual step of publishing a different

interpretation of her own paper. “When you write

a paper with 15 different people, not everyone’s

perspective can be included,” Røyrvik says.

The response, published in Antiquity and

co-authored with Oxford University archaeologist

Jane Kershaw, offered an “alternate interpretation”

of the PoBI data regarding Danish Vikings — one

that integrated archaeological evidence as well

as historical and linguistic clues. For example,

Kershaw and Røyrvik noted the scores of Viking

Age brooches unearthed in rural England. These

brooches were more than family heirlooms or

status-associated jewelry: They were basic wardrobe

necessities, worn daily to keep a woman’s outer,

apron-like dress from falling off. The number of

brooches found points to whole families, not just an

occupying force, present across the area.

Røyrvik stresses that she stands by the bulk of

the Nature paper. “On the basis of one sentence

being incorrect, it doesn’t mean the entire paper

is incorrect,” she says. The story behind the 2015

paper’s conclusions about Danish influence

provides a cautionary tale of how DNA-based

studies of historical populations can go awry.

The trouble began when researchers sought

non-British populations to compare with their

samples. “We collected a lot of very well-sourced

samples from British people,” Røyrvik says. “Quite

late in the day, the comparison with European

populations was done. We tried to get funding but

the EU didn’t go for it.”

Without the European Union’s financial support,

the team pulled together data from previous studies,

some of them with a very different focus. Danish

genetic signatures, for example, came from the

DNA of multiple sclerosis patients at a Copenhagen

hospital who had participated in an earlier MS

study. There was no genetic material from a control

population of healthy Danes, nor was there any

information about the patients’ hometowns.

“It wasn’t ideal. It was the endpoint of a lot of

different processes,” Røyrvik says.

The lack of carefully sourced modern Danish

DNA meant that the Danish genetic signature was

not as well-defined as it would have been had the

researchers sampled a population in Denmark with

the same methodology they used for participants

in Britain. It may seem like splitting hairs, but

without a clear Danish signal, it was much harder

to separate Danish Viking patterns from those of

another northern European population present

in Britain: Just a few hundred years before the

Vikings, Anglo-Saxons from northern Germany

had landed in England, and many had settled.

“There is an overlap of geography, and they’re

also very close temporally,” Røyrvik says

of the two northern European groups.

She believes that genetic signatures

interpreted as Anglo-Saxon in the Nature

paper may have been at least partly from

Danish Vikings.

“With any given scientific paper, you

hope the data is correct, and ours was

excellent. You hope the analysis of the

data is correct, and I believe ours was. The

interpretation is the issue,” Røyrvik says.

The Littlest Vikings

While unraveling the genomes of the Vikings and

their descendants makes headlines, a humbler

source of DNA is providing some of the most

intriguing clues to their lost history. Just ask

Cornell University’s Jeremy Searle, an evolutionary

biologist whose team uses small mammals —

particularly mice — to track historical human

movement.

Because it’s especially difficult to obtain

ancient mouse DNA — genetic matter in the

small bones degrades faster than in that of

larger animals, and there’s often not enough left

to sample — Searle and his team compare the

DNA from modern, geographically diverse mice.

Much of their work focuses on the house mouse

(Mus musculus), which evolved to be commensal

with humans: The mice are not domesticated like

dogs or sheep, but they are dependent on living in

and around a human settlement.

Searle’s Viking research began with a startling

discovery more than a decade ago, while helping a

student analyze mouse DNA from the Portuguese

island of Madeira, more than 400 miles off the

coast of Morocco. Searle was initially comparing

the genetic signatures of the Madeira sample

with other mouse DNA by hand, a slow and

March 2018^ DISCOVER^29

Viking women

often wore

ornate brooches

as part of

their everyday

clothing; scores

of the brooches

have been found

in England.

Jeremy Searle