30 DISCOVERMAGAZINE.COM
JAY SMITHpainstaking process that has since been largely
replaced by computer programs.
“I expected [the Madeira mouse DNA] would
match with sequences from Portugal — Madeira
was discovered by the Portuguese, colonized by
the Portuguese, and the bulk of movement via
ports was with Portugal,” says Searle. “When
I compared the sequences by eye, they didn’t
link up with Iberia at all, but were identical to
northern Europe.”
Further analysis, including ancient DNA
sequencing published by a second team in 2014,
confirmed a strong link in the genetic signatures of
Madeira mice with mice that lived among Danish
Viking Age populations. Although there is no
archaeological or historical record of the Vikings
landing on Madeira, Searle believes one of their
ships may have been blown off course, ending upon the remote Atlantic island. The Vikings’ stay on
the island was apparently brief, just long enough
for a few stowaway rodents to take some shore
leave that ended up being permanent.
Similar research since has found what may be
the genetic signatures of Norwegian Viking Age
mice in modern populations on the Azores, an
island chain more than 900 miles west of Portugal.
Mice, says Searle, make particularly goodsurrogates, or bioproxies, for human movement.
“Apart from humans and some domestics that
humans brought with them, mice are the most
globally distributed mammals,” he says. “They
reproduce quickly and can get onto vehicles and
boats. And when you’re trying to understand
human history and movement, you’re talking
about boats and caravans.”
Despite the occasional unintentional global
hitchhiking, mice are relative homebodies. They
generally stay within a territory of a few hundred
feet, so they’re unlikely to colonize new areas
unless human movement takes them there.
“Mice were accidentally dropped, left like a
pottery shard,” says Searle. “But unlike a pottery
shard, these living artifacts have DNA, which is
an extraordinary encyclopedia of information that
you can now use in a very sophisticated way.”
And using mice as bioproxies can tell us not only
where the Vikings traveled, but also how many of
them occupied a place. Says Searle: “Where you have
more people, you’re likely going to have more mice.”The Viking Cods
University of Oslo evolutionary biologist Sanne
Boessenkool and her botanist colleague Anneleen
Kool are three years into exploring a question that
flips Searle’s research on its head.
“We’re not using plants and animals to figure
out where the Vikings went,” says Boessenkool.
“We’re using where the Vikings went to find out
what they did with the plants and animals.”
At the outset of their multiyear project, Kool
and Boessenkool planned to base their research
exclusively on ancient flora and fauna DNA
samples from museum collections and some fresh
excavations. But all ancient DNA is prone to
degradation and contamination from both microbes
in the environment and modern human handling —
and ancient plant DNA is even more fragile.
“We wondered, are we going to get any DNA?”
recalls Boessenkool. “The answer was no.”
Instead of abandoning the Viking flora project
altogether, Kool is now working with linguists
to use plant names as a kind of substitute for
DNA to trace the spread of their use, and how
that use evolved.
Their work on ancient DNA from Viking Age
horses is more promising: Kool and Boessenkool
have collected about 100 samples, in different
states of preservation, from which they hope to
build a detailed picture of how equine populations
moved and changed.
“We have no idea what story will be told, but
we’re going to have a good data set to tell it with,”
says Boessenkool.
University of Oslo biologist Bastiaan Star“We can sequence DNA,
but without knowing
the stories, the context,
it’s meaningless,” says an
evolutionary biologist.