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science.org SCIENCEmultiply; the embryo is then transferred to
a surrogate mother. In 1995, Dolly the sheep
was the first animal to be born from clon-
ing. Since then, cloning has become a rou-
tine tool for duplicating farm animals, pets
including cats and dogs, and even prized
racing camels.
Cloning for conservation has a far patch-
ier history. When black-footed ferret breed-
ers first approached Revive & Restore, for
instance, researchers had created clones of
just three endangered species, all hoofed
animals: the gaur (Bos gaurus) and Eu-
ropean mouflon (Ovis aries musimon) in
2001, and the banteng (B. javanicus) in
- In 2015, scientists cloned a fourth
endangered species, a sheep known as the
Esfahan mouflon (O. gmelini isphahanica).
All died fairly young (the banteng lived
longest, dying of injuries at age 7), and pro-
duced no offspring.
In part, cloning endangered animals has
proved harder than duplicating livestock or
pets because breeding and husbandry prac-
tices are less developed in these species.
Conservation programs also have fewer
resources than commercial enterprises, so
they’re less likely to try again after an un-
successful attempt.
Cloning endangered species faces unique
ethical questions, as well. One is whether
the clone, which can hold trace DNA from
its surrogate mother, is actually the same
as the species that researchers are trying
to save. For example, black-footed ferret
clones are created using eggs from domes-
tic ferrets, meaning they carry that species’
mitochondrial DNA, which is left in the egg
after its nucleus is extracted.
Some conservationists have other con-
cerns. They worry the ability to clone a
rare species might undermine support for
efforts to protect habitat and keep species
alive in the wild. And cloning can be expen-
sive, potentially diverting funds from other
conservation activities.
“I think cloning certainly has a future
for endangered species, but there are some
problems,” says Barbara Durrant, director
of reproductive sciences with the San Diego
Zoo Wildlife Alliance. For each species, “We
will need to be very careful to do the basic
research,” she adds.
A few years ago, after extensive technical
and ethical reviews, federal regulators de-
cided the potential benefits of cloning the
ferrets outweighed the risks. Then, with per-
mits in hand, Revive & Restore teamed up
with firms including a pet cloning company
called ViaGen Pets and a commercial ferret
breeder to develop a plan that cost about
$40,000 to execute. It called for creating em-
bryos with DNA taken from Willa, the female
black-footed ferret that had died in 1988. GRAPHIC: V. ALTOUNIAN/
SCIENCE1985–Deepening the gene pool
By cloning a black-footed ferret that died in 1988, biologists hope to add greater genetic diversity to the
existing population of this endangered species, which relies heavily on captive breeding for survival.2020202220220222In Wyoming, biologists capture 18 of the last known wild
ferrets to start a captive breeding program (left).
They freeze cells from one male and one female (right).Even ViaGen’s lead scientist, Shawn
Walker, wasn’t sure whether it would work.
“We knew we had all the boxes checked,”
he says. “But until you hear that heartbeat,
you’re always a little bit skeptical, because
everything was so new.”
In late 2020, the team implanted Willa-
based embryos into three domestic ferrets
and shipped them to the National Black-
footed Ferret Conservation Center in Colo-
rado, where about two-thirds of the nation’s
captive population lives. To their relief,
one ferret gave birth to Elizabeth Ann on
10 December 2020. “It was very exciting,”
says Robyn Bortner, captive breeding man-
ager at the facility, who was in the room
when the clone was born.
But success still wasn’t a sure thing. The
other two pregnancies failed, and Elizabeth
Ann had a stillborn litter mate. And when
keepers placed Elizabeth Ann with a secondsurrogate mother and domestic siblings,
she often ended up in a dangerous spot: at
the bottom of the pile of kits. “It was touch
and go the first couple of days. ... We kept
an incredibly close eye on her,” Bortner re-
calls. But once Elizabeth Ann’s eyes opened
about 1 month later, her black-footed fer-
ret feistiness kicked in. Ever since, Bortner
says, “She’s been healthy and everything
you would hope.”NOW FULLY GROWN, Elizabeth Ann looks and
sounds like any other black-footed ferret.
She scarfs down meat and stalks and kills
live hamsters. (The keepers aren’t willing
to risk giving her a live prairie dog, which
weighs more than she does.) She chatters
angrily at caretakers who get too close. She
loves to attack and shred paper bags. And
apart from her mitochondrial DNA, most
of which comes from her domestic mother,Colored bands
represent genetic
variation.Biologists hope
to clone the male
in the future.Only seven bred
successfully.Breeding has produced more than
10,000 ferrets. All are descendants of those
seven. Genetic variation declined by 55%.Biologists will try to breed Elizabeth Ann with a captive male.
Offspring could add Willa’s DNA to the population,
increasing genetic diversity and improving the odds of survival.Willa’s DNA was used
to produce a clone,
Elizabeth Ann.Cloning efforts have
focused on the female,
named Willa.136 14 JANUARY 2022 • VOL 375 ISSUE 6577
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