Pasarea DODO & alti chitzorani

Ten extinct beasts that could walk the Earth again

* 07 January 2009 by Henry Nicholls
* Magazine issue 2690.

The Dodo, Raphus cucullatus, is one of the most well-known extinct
animals (Image: Photo Researchers / SPL)

The Dodo, Raphus cucullatus, is one of the most well-known extinct
animals (Image: Photo Researchers / SPL)

THE recipe for making any creature is written in its DNA. So last
November, when geneticists published the near-complete DNA sequence of
the long-extinct woolly mammoth, there was much speculation about
whether we could bring this behemoth back to life.

Creating a living, breathing creature from a genome sequence that
exists only in a computer's memory is not possible right now. But
someone someday is sure to try it, predicts Stephan Schuster, a
molecular biologist at Pennsylvania State University, University Park,
and a driving force behind the mammoth genome project.

So besides the mammoth, what other extinct beasts might we coax back
to life? Well, it is only going to be possible with creatures for
which we can retrieve a complete genome sequence. Without one, there
is no chance. And usually when a creature dies, the DNA in any flesh
left untouched is soon destroyed as it is attacked by sunshine and
bacteria.

There are, however, some circumstances in which DNA can be preserved.
If your specimen froze to death in an icy wasteland such as Siberia,
or snuffed it in a dark cave or a really dry region, for instance,
then the probability of finding some intact stretches of DNA is much
higher.

Even in ideal conditions, though, no genetic information is likely to
survive more than a million years - so dinosaurs are out - and only
much younger remains are likely to yield good-quality DNA. "It's
really only worth studying specimens that are less than 100,000 years
old," says Schuster.

The genomes of several extinct species besides the mammoth are already
being sequenced, but turning these into living creatures will not be
easy (see "Revival recipe"). "It's hard to say that something will
never ever be possible," says Svante Pääbo of the Max Planck Institute
for Evolutionary Anthropology in Leipzig, Germany, "but it would
require technologies so far removed from what we currently have that I
cannot imagine how it would be done."

But then 50 years ago, who would have believed we would now be able to
read the instructions for making humans, fix inherited diseases, clone
mammals and be close to creating artificial life? Assuming that we
will develop the necessary technology, we have selected 10 extinct
creatures that might one day be resurrected. Our choice is based not
just on feasibility, but also on each animal's "megafaunal charisma" -
just how exciting the prospect of resurrecting these animals is.

Of course, bringing extinct creatures back to life raises a whole host
of practical problems, such as where they will live, but let's not
spoil the fun...
Sabre-toothed tiger

(Smilodon fatalis)

Extinct: ~10,000 years ago
DNA preservation: 3/5
Suitable surrogate: 3/5

This fabled beast with its extraordinary canines would be a sight to
behold. There are some spectacularly preserved sabre-toothed specimens
from the La Brea tar pits in Los Angeles, but the tar makes extracting
DNA tricky, so nobody has been able to isolate decent sequences.
However, there are also some permafrost-preserved specimens that might
be a better source of DNA. If we could obtain a genome, a close living
relative of the sabre-tooth, the African lion, should be a good egg
donor and surrogate mother. Californians, beware!
Neanderthal

(Homo neanderthalensis)

Extinct: ~25,000 years ago
DNA preservation: 1/5
Suitable surrogate: 5/5

A draft sequence of the Neanderthal genome should be published
sometime this year. "To have a reasonable-quality genome, say
comparable to the chimpanzee, will then be another two years of work
or so," says Svante Pääbo of the Max Planck Institute for Evolutionary
Anthropology in Leipzig, Germany. While he and his colleagues hope the
genome will offer unique insights into the differences between us
humans and our mysterious cousins, there is speculation it could also
be used to resurrect the Neanderthal. Because of our very close shared
ancestry, humans would make ideal egg donors and surrogate mothers.

However, while Soviet scientists might once have tried to create a
human-ape hybrid, today it is hard to imagine even the most crazed of
mad scientists entering such taboo territory. "I find the idea of
resurrecting the Neanderthal so ridiculous that any speculation on
surrogate mothers is superfluous," says Pääbo. At most, researchers
might replace some human genes with the Neanderthal versions in cells
growing in a dish to see what the effect is, he says.
Short-faced bear

(Arctodus simus)

Extinct: ~11,000 years ago
DNA preservation: 3/5
Suitable surrogate: 2/5

This towering beast would dwarf the world's largest living land
carnivore, the polar bear. The short-faced bear may have been a third
taller than the polar bear when standing upright, and it weighed up to
a tonne. Recovering its DNA should be possible as there are specimens
encased in permafrost. The short-faced's closest living relative is
the spectacled bear of South America. The two species parted
evolutionary company only around 5 million years ago, but
unfortunately, at just a tenth the body mass of the short-faced bear,
the spectacled bear is unlikely to be a particularly good surrogate.
Tasmanian tiger

(Thylacinus cynocephalus)

Extinct: 1936
DNA preservation: 4/5
Suitable surrogate: 1/5

The last Tasmanian tiger or thylacine - an individual that has become
known as Benjamin - died in Hobart Zoo in 1936. The existence of
various preserved tissues less than a century old means geneticists
should be able to get good-quality DNA and produce a complete sequence
of the thylacine genome before too long. When it comes to
resurrection, marsupials like the thylacine might be easier than most
other mammals. Pregnancy in marsupials typically lasts just weeks, and
a simple placenta forms only briefly, meaning there might be less risk
of incompatibility between an embryo and a surrogate mother of another
species. For the thylacine, the surrogate would be the Tasmanian
devil. After birth, the fetus could be raised on milk in an artificial
pouch.
Glyptodon

(Doedicurus clavicaudatus)

Extinct: ~11,000 years ago
DNA preservation: 2/5
Suitable surrogate: 1/5

The Volkswagen Beetle-sized "colossal" armadillo, with its spiky, club-
like tail, once rumbled across the South American countryside, and
some might fancy seeing it do so again. Because there are no frozen
glyptodons, obtaining usable DNA will depend on finding well-preserved
remains in a cool, dry cave. Beyond that, there is an even bigger
problem: the most suitable species to act as a host for a developing
glyptodon embryo would be the far smaller 30-kilogram "giant"
armadillo. The difference in size means it would struggle to carry its
extinct relative to term.
Woolly rhinoceros

(Coelodonta antiquitatis)

Extinct: ~10,000 years ago
DNA preservation: 4/5
Suitable surrogate: 5/5

Resurrecting the woolly rhino has lots going for it. As with the
mammoth, there are plenty of specimens preserved in permafrost, and
the availability of hair, horns and hooves is a big plus. These
tissues can be cleaned up with shampoo and bleach to remove
contaminant DNA from microbes and fungi before using enzymes to
release an abundance of near-pure rhino DNA. This makes it likely that
geneticists will publish the complete genome of this hirsute beast
before long. However, although the woolly rhino has close living
relatives that might make suitable surrogates, all contemporary rhino
species are themselves on the brink of extinction. As long as this
remains the case, resurrecting a woolly rhino is unlikely to be a top
priority.
Dodo

(Raphus cucullatus)

Extinct: ~AD 1690
DNA preservation: 1/5
Suitable surrogate: 3/5

In 2002, geneticists at the University of Oxford got permission to cut
into the world's best-preserved dodo specimen, a foot bone - complete
with skin and feathers - held under lock and key at the university's
Museum of Natural History. "It was one of the scariest things I've had
to do," recalls Beth Shapiro, an ancient DNA specialist now at
Pennsylvania State University. This yielded minute fragments of dodo
mitochondrial DNA but nothing more. Since then, no other specimen has
yielded even a whiff of dodo DNA, but there is still hope that some
will one day be found. "We're still looking," says Shapiro. If one
turns up and a genome sequence could be produced from it, it would
then be down to pigeons to help bring their famous cousin back from
the dead.
Giant ground sloth

(Megatherium americanum)

Extinct: ~8000 years ago
DNA preservation: 2/5
Suitable surrogate: 1/5

This giant stood around 6 metres tall and is estimated to have weighed
a whopping 4 tonnes. The sloth's relatively recent extinction means
that several specimens have been found with hair, an excellent source
of DNA. So are we likely to see the giant sloth genome published?
"Absolutely," says Hendrik Poinar of MacMaster University in Canada,
who has extracted giant ground sloth DNA from fossilised dung
deposited some 30,000 years ago. The difficulty for anyone intent on
resurrection would be the lack of a suitable surrogate. Its closest
living relative - the three-toed tree sloth - is tiny by comparison.
It might be able to provide eggs with which to create a giant ground
sloth embryo, but the fetus would quickly outgrow its surrogate
mother.
Moa

(Dinornis robustus)

DNA preservation: 3/5
Suitable surrogate: 2/5

There is plenty of moa DNA to be found in well-preserved bones and
even eggs in caves across New Zealand, so obtaining a moa genome
should be doable. But which one? It would be tempting to go for the
massive Dinornis robustus, which stood more than 3 metres tall, but
starting with the more modestly sized Megalapteryx didinus might make
more sense. Although only distantly related to ostriches, it might be
possible to boot up the moa genome in an ostrich egg. As no bird has
yet been cloned, however, perhaps the most feasible approach would be
to engineer an ostrich embryo to be moa-like.
Irish elk

(Megaloceros giganteus)

Extinct: ~7700 years ago
DNA preservation: 3/5
Suitable surrogate: 2/5

Deer-hunting enthusiasts would give almost anything for a chance to
stalk this Pleistocene giant, once found across Europe. A typical male
Megaloceros stood more than 2 metres tall at the shoulder and sported
antlers 4 metres wide. It is actually a deer rather than an elk, and
its closest living relative is the much smaller fallow deer, the two
species having parted evolutionary company around 10 million years
ago. The gulf between the two species means it is hard to see how a
complete genome could be converted into a living, breathing animal.
Giant beaver

(Castoroides ohioensis)

Extinct: ~10,000 years ago
DNA preservation: 2/5
Suitable surrogate: 1/5

There is fierce controversy over the reintroduction of normal beavers
in some countries, so imagine how much fuss there would be over the
reintroduction of the 2.5-metre-long giant beaver to North America.
It's not too much to hope for a genome sequence of this massive
rodent, says Hendrik Poinar, a geneticist at McMaster University in
Hamilton, Canada. The capybara, which is about half the mass, would
probably be the most suitable surrogate, though it might still be too
distant a relative.
Gorilla

(Gorilla gorilla)

Extinct: Almost
DNA preservation: 5/5
Suitable surrogate: 5/5

The first species to be brought back from extinction will most likely
be one that is alive today. Conservationists are freezing tissue
samples from some threatened species, so clones could be created with
the help of a closely related surrogate species if a suitable habitat
becomes available. For gorillas, the surrogate would be the
chimpanzee.
Revival recipe

YOU WILL NEED:

* Well-preserved DNA
* Several billion DNA building blocks
* A suitable surrogate species
* Some seriously advanced technology

HERE'S WHAT TO DO...

1. Extract the DNA from your extinct species, sequence the fragments
and assemble to obtain a complete genome.

REALITY CHECK: genome sequences from extinct animals are likely to be
riddled with lethal errors.

2. Now take your DNA building blocks and recreate the DNA of your
extinct beast, in the correct number of chromosomes.

REALITY CHECK: it is not yet possible to make such long DNA molecules
from scratch, but we should be able to one day.

3. Package the chromosomes up into an artificial nucleus and pop it in
an egg collected from your suitable surrogate species. This should
then develop into an embryo, which will be a clone of a long-dead
animal.

REALITY CHECK: finding compatible species, let alone extracting eggs
from them, could be a huge problem. Plus, no one has yet managed to
clone birds or reptiles.

4. Grow a baby animal from the embryo. For mammals, implant the embryo
in the womb of a compatible surrogate mother. For a reptile or bird,
incubate embryo using yet-to-be-developed techniques. For an amphibian
or fish where fertilisation takes place outside the body, just sit
back and watch.

REALITY CHECK: compatible surrogate mothers may not exist for many
extinct mammals.

HOW TO CHEAT:

Rather than synthesising the entire genome from scratch, you could
take the DNA of a closely related living species and modify it to be
more like that of the extinct species you are aiming for.

REALITY CHECK: some living species have already been made
superficially more like extinct ones, but with today's knowledge and
technology they remain far from the real thing.

Henry Nicholls is a science writer based in London, and author of
Lonesome George (Macmillan, 2006)
.

Relevant Pages

  • Re: Ping Rumple
    ... A "Eugenics plan" sounds very dangerous to me, ... for individuals and for whole species. ... I don't think that you can claim with any degree of certainty that any species that becomes extinct might not appear again if the evolutionary environment favors it. ... In the DNA study of biological evolution, it has been shown that the tree of life is, in fact, not a tree but a network of reconvergent branches. ...
    (soc.retirement)
  • Re: Ping Rumple
    ... undesirable would reduce genetic diversity by definition. ... for individuals and for whole species. ... I don't think that you can claim with any degree of certainty that any species that becomes extinct might not appear again if the evolutionary environment favors it. ... In the DNA study of biological evolution, it has been shown that the tree of life is, in fact, not a tree but a network of reconvergent branches. ...
    (soc.retirement)
  • Re: Ping Rumple
    ... undesirable would reduce genetic diversity by definition. ... for individuals and for whole species. ... I don't think that you can claim with any degree of certainty that any species that becomes extinct might not appear again if the evolutionary environment favors it. ... In the DNA study of biological evolution, it has been shown that the tree of life is, in fact, not a tree but a network of reconvergent branches. ...
    (soc.retirement)
  • Re: Ping Rumple
    ... undesirable would reduce genetic diversity by definition. ... A "Eugenics plan" sounds very dangerous to me, ... If we'd gone extinct, we ... In the DNA study of biological evolution, ...
    (soc.retirement)
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