segunda-feira, 27 de abril de 2015
A mammoth project that raises hairy ethical qualms
Shaggy of coat and extravagantly curled of tusk, woolly mammoths were the iconic species of the Ice Age. These cousins of the Asian elephant last lumbered across the planet around 6,000 years ago; a dwarf species survived on Wrangel Island, a Russian Arctic wilderness, until 4,000 years ago.
They could lumber once more if scientists have their way. A number of breakthroughs — including the insertion of mammoth DNA into living elephant cells, techniques to “edit” existing genomes and stitch together new ones, and, as announced last week, the decoding of the mammoth genome — has revived enthusiasm for so-called mammoth “de-extinction”.
The concept of resuscitating long-lost species is fashionable: a charity in the UK is consulting on whether wild lynx, which disappeared about 1,300 years ago from the British Isles, should be released to control deer numbers (there is public support but farmers fear the big cats will attack livestock).
On occasion, the idea of reintroducing species may have some environmental merit, as with the lynx. Mammoths once grazed the tundra of Eurasia, and one argument is that restoring these herbivores could help to mitigate climate change by keeping the tundra colder.
But attempts to knit a living woolly mammoth from scratch are misguided, mostly for reasons of animal welfare. Recent findings suggest that mammoths may not have died out, as popularly believed, through overhunting or inbreeding, but due to climate change. The wisdom of welcoming them back to a warming world is questionable.
The mammoth revival project is led by George Church at Harvard University, and supported by the Long Now Foundation. Dr Church has noted that the Asian elephant is a closer genetic relative to the mammoth than to the African elephant. The easiest route to resurrection would be to find a living mammoth cell and clone it, using an Asian elephant as a surrogate. Alas, no living mammoth cells have been discovered.
But scraps of decayed DNA do regularly turn up, lurking in bones rendered visible by melting permafrost. These mammoth DNA fragments indicate which genetic tweaks could be made to an elephant embryo to result in a more mammoth-like creature. Crucial genes conferring resistance to cold could be inserted, resulting in a thick layer of fat, deep fur and smaller ears (to cut heat loss). This genetic “cut and paste” effort works in principle: the Harvard team claimed last month that 14 artificially created mammoth genes were successfully sewn into a living elephant cell.
Gene-editing technology, however, cannot resolve the estimated 70m genetic differences between mammoths and Asian elephants. Scientists would have to settle with a part-elephant, part-mammoth hybrid, to be implanted in a female elephant. As the biologist Beth Shapiro, author of How to Clone a Mammoth, points out, it is uncertain how this chimera would develop, bathed as it is in elephant hormones.
None of this has deterred a South Korean team, which announced last year it would use DNA from blood samples from a well-preserved Siberian specimen to create a mammoth “within our generation”.
If born, any calf is likely to spend its childhood in captivity, learning to be . . . what? Not a mammoth because its elephant mother cannot teach that. The idea of a social, intelligent animal being released into the wild, alone and unversed in the skills required for mammoth survival, is disturbing.
That is not to dismiss all revivalist attempts; the Long Now Foundation also longs to bring back the passenger pigeon, which became extinct in 1914. But in the roll call of extinct genomes, there is something cartoonish about alighting on the biggest of them all for resurrection. Recreating the mammoth would be spectacular — but more as a Disneyesque showpiece of human vanity than an environmental fix.
Anjana Ahuja is a science commentator