“Danger, “ says the sign on the door of a laboratory at the Australian Museum in
Sydney: “Tasmanian Tiger, Trespassers will be eaten!” The joke is that the Tasmanian
tiger—a beloved symbol of the island state that appears on its license plate—has been
extinct for nearly seven decades. But researchers behind that door are working to bring
the animal back to life by cloning it, using DNA extracted from specimens preserved
decades ago. Among other things, the work raises questions about the nature of
extinction itself.
A
The Tasmanian tiger’s Latin designation, Thylacinus cynocephalus, or “dogheaded
pouched-dog,” makes it redundantly clear that the marsupial’s feline
nickname is a misnomer. Yet its striped coat was cat-like, which runs nearly
shoulder to tail. The animal had large, powerful jaws, which secured the
predator a place atop the local food chain. Females carried their young in
backward-facing pouches. Thylacines, once spread throughout mainland
Australia and as far north as New Guinea, were probably outcompeted for food
by the dingoes ( 猎狗) that humans introduced to the area some 4,000 years
ago, says Australian Museum director Mike Archer, founder of the cloning
project. Eventually, thylacines remained only on the dingo-free island of
Tasmania, south of the mainland. But with the arrival of European settlers in
the 1800s, the marsupial’s days were numbered. Blamed (often wrongly) for
killing livestock, the animals were hunted indiscriminately. The government
made thylacines a protected species in 1936, but it was too late; It was a frigid
winter night in 1936. A lone Tasmanian tiger huddled in his— or her— open
enclosure at Hobart Zoo. With nowhere to shelter from the cold and no keepers
to care, the delicately striped animal died. When this solitary animal—whose
sex was not even recorded because of lack of interest—died, so did an entire
species, the last specimen reportedly died in captivity the same year. What’s
more, with the passing into extinction of the Tasmanian tiger, Thylacinus
cynocephalus, it was the end of the line for an entire family of marsupials that
had lived in Australia for millions of years.
B
The Australian researchers set out to bring the animal back partly to atone
for humanity’s role in its extinction, Archer says. The idea took root 15 years
ago when he saw a pickled thylacine pup in the museum’s collection. “It
jarred me and started me thinking,” recalls the 58-year-old paleontologist and
zoologist, who received his undergraduate degree from Princeton University
and his doctorate from the University of Western Australia. “DNA is the
recipe for making a creature. So if there is DNA preserved in the specimen,
why shouldn’t we begin to use technology to read that information, and then
in some way use that information to reconstruct the animal? I raised the issue
with a geneticist. The response was derisive laughter.”
C
Then, in 1996, Dolly the sheep burst onto the scene and, suddenly, Archer says,
“cloning wasn’t just a madman’s dream.” Dolly proved that DNA from an
ordinary animal cell— in her case, a ewe’s udder— could generate a virtually
identical copy, or clone, of the animal after the DNA was inserted into a treated
egg, which was implanted in a womb and carried to term. Archer’s goal is
even more ambitious: cloning an animal with DNA from long-dead cells,
reminiscent of the sci-fi novel and movie Jurassic Park. The challenge? The
DNA that makes up the chromosomes in which genes are bundled falls apart
after a cell dies.
D
Researchers working with Don Colgan, head of the museum’s evolutionary
biology department, extracted DNA from a thylacine pup preserved in alcohol
in 1866, and biologist Karen Firestone obtained additional thylacine DNA
from a tooth and a bone. Then, using a technique called polymerase chain
reaction, the researchers found that the thylacine DNA fragments could
be copied. The scientists next have to collect millions of DNA bits and
pieces and create a “library” of the possibly tens of thousands of thylacine genes—
a gargantuan task, they concede. Still, an even greater obstacle looms, that of stitching all those DNA fragments together properly into functioning chromosomes; the scientists don’t
know how many chromosomes a thylacine had, but suspect that, like related
marsupials, it had 14. But no scientist has ever synthesized a mammalian
chromosome from scratch. If the Aussie scientists accomplish those feats,
they may try to generate a thylacine by placing the synthetic chromosomes
into a treated egg cell of a related species— say, a Tasmanian devil, another
carnivorous marsupial—and implant the egg in a surrogate mother.
E
Such cross-species cloning, as the procedure is called, is no longer fantasy.
In 2001, Advanced Cell Technology (ACT) of Worcester, Massachusetts,
succeeded in cloning, for the first time, an endangered animal, a rare wild ox
called a gaur. This past April, scientists from ACT, Trans Ova Genetics of
Sioux Center, Iowa, and the Zoological Society of San Diego announced they
had cloned a banteng, an endangered wild bovine species native to Southeast
Asia, using a domesticated cow as a surrogate mother. Meanwhile, researchers
in Spain are trying to clone an extinct mountain goat, called a bucardo, using
cells collected and frozen before the species’ last member died in 2000. Other
scientists hope to clone a woolly mammoth from 20,000-year-old specimens
found in Siberian permafrost.
F
Many scientists are skeptical of the thylacine project. Ian Lewis, technology
development manager at Genetics Australia Cooperative Ltd., in Bacchus
Marsh, Victoria, Australia, says the chances of cloning an animal from
“snippets” of DNA are “fanciful.” Robert Lanza, ACTs medical director and
vice president, says cloning a thylacine is beyond existing science. But it may
be within reach in several years, he adds: “This area of genetics is moving
forward at an exponential rate.”
G
In Australia, critics say the millions of dollars that the thylacine project will
cost would be better spent trying to save endangered species and disappearing
habitats. One opponent, Tasmanian senator and former Australia Wilderness
Society Director Bob Brown, says people might become blase about
conservation if they’re lulled into thinking
a lost species can always be resurrected.
The research “feeds the mind-set that
science will fix everything,” he says.
Another concern touches on the great nature-nurture quandary: Would a cloned
thylacine truly represent the species, given that it would not have had the
chance to learn key behaviors from other thylacines? For some carnivores, says
University of Louisville behavioral ecologist Lee Dugatkin, “it’s clear that
young individuals learn various hunting strategies from parents.” And a foster
parent might not fill the gap. Dugatkin asks whether a cloned Tasmanian tiger
raised by a surrogate Tasmanian devil would just be a devil in tiger’s clothing.
H
But Archer says, in effect, a thylacine is a thylacine, however its DNA
blueprint is obtained, because much animal behavior, including that of
marsupials, is genetically hardwired or instinctual. We take kittens and raise
them with humans, but they still behave like cats,” he points out. And Archer,
who envisions nature preserves populated by cloned thylacines and their
offspring, says the project is actually a boon to conservation: it shows what it
takes just to contemplate resurrecting a vanished species. For now, Archer and
coworkers are trying to piece together the thylacine’s exact genetic makeup.
14 striped coat
15 Australia
16 4000 years
17 Tasmania
18 European (settlers)
19 captivity
20 E
21 F
22 A
23 D
24 B
25 A
26 C
27 D
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