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  • The idea of de-extinction is that we can bring back species that are now completely gone.

  • The major flashpoint of interest in what has now led to de-extinction technology happened

  • about 10 years ago when Dolly the sheep was created. In many ways, Dolly was the harbinger

  • of the kind of technology that will permit us to do even more sophisticated kinds of

  • creation of species that used to exist, species that still exist and perhaps even species

  • that never existed.

  • We can group relevant methods into three large categories. There's back-breeding which humans

  • have practiced literally for thousands and thousands of years.

  • This is being done right now in Western Europe, trying to recreate what's known as the aurochs.

  • The way cows look today is not the way the cattle family looked 10,000 years ago. So,

  • if your problem is to recreate one of those primitive cows, what do you do? Well you reach

  • back into the genetic code by selecting for animals that have slightly longer horns or

  • a bigger bulk or the kind of hide coloration that you think is appropriate. It is a very

  • viable and low-tech way of de-extinction.

  • And the investigators trying to do this back-breeding to aurochs have had some success. The animals

  • look quite a bit like old representations that go right back to cave paintings.

  • But what is it really? What it is really is a constellation of traits that you've selected

  • for and you know nothing, really, about how close it is physiologically to an aurochs

  • because there's no way of examining a living aurochs at present. You also don't know about

  • behavior. Behavior tends not to fossilize in any realistic manner and the degree to

  • which any modern cow resembles an aurochs in terms of behavior is a complete unknown.

  • A second method for de-extinction that has improved greatly in the last 10 years is cloning,

  • particularly the kind of cloning known as somatic cell nuclear transfer.

  • You take the genetic material -- the nucleus -- of one cell, you put it into another -- an

  • egg -- and that egg is then placed in an animal that will act as surrogate mother and produce

  • an offspring.

  • There's also been massive improvements in what we can call synthesis. Synthesis involves

  • making up our own sequence, just like in a recipe.

  • If you have two species -- one extinct, one living -- you can get the genetic material

  • of the extinct one and compare that to the living one.

  • Passenger pigeons died out, finally, almost exactly a hundred years ago. Passenger pigeons

  • have several very close relatives among pigeons and one is the band-tailed pigeon, which is

  • very close indeed. In recent years, scientists have been able to isolate the differences

  • between the genomes of extinct passenger pigeons and living band-tailed pigeons. They've been

  • able to inject these novel sequences into the germ line of developing band-tailed pigeons

  • and using surrogates with the sex cells of passenger pigeons. If you cross breed them

  • one to another, you will in the next generation get something that should look exactly like

  • a passenger pigeon.

  • Now comes the basic question here, which is: What are you going to do with passenger pigeons,

  • assuming that you go ahead and create a whole flock of them?

  • It's been estimated that there were probably more passenger pigeons than any other kind

  • of bird ever. I don't know what we would do with a billion passenger pigeons. We don't

  • like pigeons to begin with in this place.

  • A very important thing to consider about extinctions in general in the course of life on the planet

  • is that the waters close very quickly when a species disappears. What tends to happen

  • is that other species move in. This is how evolution in fact works.

  • The mammoth behind me perfectly illustrates some of the issues that we're going to face

  • with de-extinction.

  • There is no place for several more very large herbivores in a place like the U.S. except

  • under very controlled conditions. Who's going to take care of them? How are you going to

  • provision them? Are we thinking that we're going to bring back the Pleistocene by virtue

  • of having a few extinct species?

  • What we're really talking about is undertaking a whole lot of unplanned experiments, the

  • consequences of which are very hard to predict. We don't want a situation in which we drive

  • out species that are perhaps already endangered thanks to us with something else that we drove

  • to extinction thousands of years ago.

  • De-extinction to the degree it will take place should be limited in its scope, limited in

  • its ambition, limited in the kinds of species that we bring back. But if there was one animal

  • I could vote for to bring back, it would be one of these giant ground sloths.

  • If you want people to be interested in not only what the planet still has and how we

  • might conserve it, but what the planet has recently lost and perhaps most particularly

  • what it's lost because of human activities, then to see these again, to see mammoths again

  • in the flesh would be an exciting prospect.

  • It would raise rather than dampen interest in preserving what we have and what we used

  • to have.

The idea of de-extinction is that we can bring back species that are now completely gone.

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B1 中級

消滅を支える科学 (The Science Behind De-extinction)

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    Bing-Je に公開 2021 年 01 月 14 日
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