Should we try to bring extinct species back to life?
A
AFew birds have entered legend as the ashen plains-dove did. Across the grasslands of southern Argentina it once travelled in flocks so enormous — millions of birds, on occasion, moving as one — that its seasonal passage ranked among the natural world's most extraordinary sights. That spectacle ended on 19 April 1921, the day the very last of the species died in the zoological gardens at Rosario. Reviving it is now the aim of a bold undertaking led by the geneticist Dr Karl Vogel, who is pursuing what has come to be called 'de-extinction'. In essence, the method takes DNA recovered from a vanished animal, converts it into a fertilised embryo, and places that embryo inside the closest surviving relation — here, the still-plentiful widespread scrub-dove — which then carries and delivers a living creature. The plains-dove was among the first species to which the approach was applied, though far from the last, since the same advanced techniques are now being tried on many other animals.
B
BA comparable effort is under way for the Kestran wolf, a predator that once roamed the island of Kestra and disappeared roughly a century ago. 'Since the wolf was lost, no meat-eater on Kestra has taken over the role it used to play,' notes Professor Ravi Anand of the University of Otago. In the years after the animal vanished, he explains, a severe and disfiguring facial-tumour disease has spread through the population of Kestran quolls — the small marsupial for which the island is otherwise best known — and now endangers their survival. Had the wolves remained, Anand argues, they would have killed enough quolls to keep the sickness in check. 'A contagious cancer of that sort, arising in earlier times, would simply have died out wherever it first appeared. Bringing the wolf back to Kestra might guarantee that the quolls are never exposed to such a danger again.'
C
CSupposing lost species really can be revived, might our kind at last begin to undo the harm done to nature over the last few thousand years? 'What de-extinction promises is a reversal — a way of restoring creatures that have ceased to exist,' says Dr Lena Haas, of the Genomics Centre at the University of Leiden. 'My own view is that this cannot truly be achieved. Something that vanished in the distant past can never be reproduced so as to be one hundred per cent the same.' For species gone a very long time, she suggests, the more workable route is to treat a living species' DNA as a foundation and splice into it fragments of the extinct animal's genetic material. What emerges is not the old animal but a new one — a hybrid based on the living species, yet resembling the lost creature in look or behaviour.
D
DGiven how intricate the procedure is, and how uncertain its result, one might reasonably ask what the technology is really for. 'Our aim, from the start, has been to put a fitting stand-in where the extinct species used to be,' Vogel says. 'Scrub-doves nest apart from one another — perhaps a nest or two to a hectare — but plains-doves were intensely sociable birds that would pack ten thousand nests or more into that same hectare.' Once this pivotal bird was gone, the woodlands of the Argentine interior began to decline: with no thousands of plains-doves breaking branches and battering the trees, little disturbance occurred, and so little regrowth was ever called for. The forests grew static, and thus inhospitable to the very plants and creatures that had evolved to restore woodland after such disturbance. Vogel believes a scrub-dove crossed with the nesting behaviour of a plains-dove might, at least in principle, bring that disturbance back, and by doing so recreate the conditions on which a great many other native species depend.
E
EThe tundra elephant is another favourite candidate for such work. Professor Mateo Silva — who teaches at the Ashcroft Institute of Molecular Biology and heads the Tundra Elephant Revival Project — has concentrated on cold tolerance, the chief respect in which the vanished tundra elephant and its closest living cousin, the endangered lowland elephant, part company. By identifying the genetic traits that once let these animals endure the tundra's freezing climate, the team hopes to return them, or some near equivalent, to that landscape. 'Safeguarding the endangered lowland elephant is what I would put first,' Silva remarks, 'along with pushing its range out into the immense expanse of the tundra. That would call for a few adjustments — ears of a smaller size, a thicker coat of hair, added layers of insulating fat — each a means of curbing heat loss in the cold, and each present in the tundra elephant that is now gone.' Restoring large mammals to the tundra and northern Eurasia's forests might also help hold down carbon emissions: such elephants drive holes through the snow and topple trees, which favours the spread of grass, and the grass, by cooling the ground, restrains the emissions released as frozen soil thaws.
F
FReviving extinct animals may fire the imagination, yet rescuing a living species that is merely at risk of dying out is, naturally, a far simpler matter. 'A good deal of the technology people picture when de-extinction comes up can equally serve as a kind of "genetic rescue",' Haas points out. What she would rather the discussion centred on is how these new methods might reveal precisely why particular species were lost to begin with — and, from that, how the same tools could be used to make the genetic changes that would head off large-scale extinctions in years to come. 'There is, I'd add, a tremendous moral hazard in doing nothing whatsoever,' she goes on. 'What we manage today plainly falls short, and we must be prepared to take a few carefully weighed risks.'
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Question 1 - 4
Choose the correct paragraph, A-F.
A
B
C
D
E
F
1.
the reason it is impossible to recreate a species exactly as it once was
2.
a comparison of how densely two related bird species build their nests
3.
a suggestion that the technology could keep large numbers of species from disappearing in future
4.
a statement giving the exact day on which a species finally disappeared