Hendrik Poinar: Bring back the woolly mammoth!

243,203 views ・ 2013-05-30

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Translator: Joseph Geni Reviewer: Morton Bast
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When I was a young boy,
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I used to gaze through the microscope of my father
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at the insects in amber that he kept in the house.
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And they were remarkably well preserved,
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morphologically just phenomenal.
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And we used to imagine that someday,
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they would actually come to life
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and they would crawl out of the resin,
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and, if they could, they would fly away.
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If you had asked me 10 years ago whether or not
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we would ever be able to sequence the genome of extinct animals,
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I would have told you, it's unlikely.
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If you had asked whether or not we would actually be able
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to revive an extinct species,
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I would have said, pipe dream.
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But I'm actually standing here today, amazingly,
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to tell you that not only is the sequencing
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of extinct genomes a possibility, actually a modern-day reality,
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but the revival of an extinct species is actually within reach,
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maybe not from the insects in amber --
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in fact, this mosquito was actually used
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for the inspiration for "Jurassic Park" —
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but from woolly mammoths, the well preserved remains
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of woolly mammoths in the permafrost.
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Woollies are a particularly interesting,
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quintessential image of the Ice Age.
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They were large. They were hairy.
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They had large tusks, and we seem to have
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a very deep connection with them, like we do with elephants.
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Maybe it's because elephants share
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many things in common with us.
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They bury their dead. They educate the next of kin.
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They have social knits that are very close.
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Or maybe it's actually because we're bound by deep time,
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because elephants, like us, share their origins in Africa
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some seven million years ago,
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and as habitats changed and environments changed,
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we actually, like the elephants, migrated out
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into Europe and Asia.
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So the first large mammoth that appears on the scene
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is meridionalis, which was standing four meters tall
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weighing about 10 tons, and was a woodland-adapted species
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and spread from Western Europe clear across Central Asia,
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across the Bering land bridge
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and into parts of North America.
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And then, again, as climate changed as it always does,
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and new habitats opened up,
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we had the arrival of a steppe-adapted species
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called trogontherii in Central Asia
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pushing meridionalis out into Western Europe.
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And the open grassland savannas of North America
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opened up, leading to the Columbian mammoth,
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a large, hairless species in North America.
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And it was really only about 500,000 years later
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that we had the arrival of the woolly,
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the one that we all know and love so much,
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spreading from an East Beringian point of origin
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across Central Asia, again pushing the trogontherii
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out through Central Europe,
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and over hundreds of thousands of years
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migrating back and forth across the Bering land bridge
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during times of glacial peaks
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and coming into direct contact
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with the Columbian relatives living in the south,
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and there they survive over hundreds of thousands of years
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during traumatic climatic shifts.
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So there's a highly plastic animal dealing with great transitions
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in temperature and environment, and doing very, very well.
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And there they survive on the mainland until about 10,000 years ago,
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and actually, surprisingly, on the small islands off of Siberia
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and Alaska until about 3,000 years ago.
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So Egyptians are building pyramids
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and woollies are still living on islands.
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And then they disappear.
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Like 99 percent of all the animals that have once lived,
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they go extinct, likely due to a warming climate
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and fast-encroaching dense forests
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that are migrating north,
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and also, as the late, great Paul Martin once put it,
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probably Pleistocene overkill,
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so the large game hunters that took them down.
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Fortunately, we find millions of their remains
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strewn across the permafrost buried deep
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in Siberia and Alaska, and we can actually go up there
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and actually take them out.
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And the preservation is, again,
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like those insects in [amber], phenomenal.
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So you have teeth, bones with blood
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which look like blood, you have hair,
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and you have intact carcasses or heads
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which still have brains in them.
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So the preservation and the survival of DNA
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depends on many factors, and I have to admit,
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most of which we still don't quite understand,
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but depending upon when an organism dies
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and how quickly he's buried, the depth of that burial,
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the constancy of the temperature of that burial environment,
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will ultimately dictate how long DNA will survive
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over geologically meaningful time frames.
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And it's probably surprising to many of you
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sitting in this room that it's not the time that matters,
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it's not the length of preservation,
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it's the consistency of the temperature of that preservation that matters most.
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So if we were to go deep now within the bones
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and the teeth that actually survived the fossilization process,
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the DNA which was once intact, tightly wrapped
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around histone proteins, is now under attack
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by the bacteria that lived symbiotically with the mammoth
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for years during its lifetime.
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So those bacteria, along with the environmental bacteria,
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free water and oxygen, actually break apart the DNA
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into smaller and smaller and smaller DNA fragments,
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until all you have are fragments that range
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from 10 base pairs to, in the best case scenarios,
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a few hundred base pairs in length.
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So most fossils out there in the fossil record
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are actually completely devoid of all organic signatures.
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But a few of them actually have DNA fragments
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that survive for thousands,
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even a few millions of years in time.
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And using state-of-the-art clean room technology,
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we've devised ways that we can actually pull these DNAs
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away from all the rest of the gunk in there,
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and it's not surprising to any of you sitting in the room
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that if I take a mammoth bone or a tooth
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and I extract its DNA that I'll get mammoth DNA,
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but I'll also get all the bacteria that once lived with the mammoth,
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and, more complicated, I'll get all the DNA
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that survived in that environment with it,
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so the bacteria, the fungi, and so on and so forth.
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Not surprising then again that a mammoth
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preserved in the permafrost will have something
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on the order of 50 percent of its DNA being mammoth,
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whereas something like the Columbian mammoth,
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living in a temperature and buried in a temperate environment
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over its laying-in will only have 3 to 10 percent endogenous.
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But we've come up with very clever ways
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that we can actually discriminate, capture and discriminate,
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the mammoth from the non-mammoth DNA,
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and with the advances in high-throughput sequencing,
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we can actually pull out and bioinformatically
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re-jig all these small mammoth fragments
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and place them onto a backbone
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of an Asian or African elephant chromosome.
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And so by doing that, we can actually get all the little points
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that discriminate between a mammoth and an Asian elephant,
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and what do we know, then, about a mammoth?
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Well, the mammoth genome is almost at full completion,
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and we know that it's actually really big. It's mammoth.
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So a hominid genome is about three billion base pairs,
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but an elephant and mammoth genome
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is about two billion base pairs larger, and most of that
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is composed of small, repetitive DNAs
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that make it very difficult to actually re-jig the entire structure of the genome.
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So having this information allows us to answer
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one of the interesting relationship questions
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between mammoths and their living relatives,
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the African and the Asian elephant,
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all of which shared an ancestor seven million years ago,
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but the genome of the mammoth shows it to share
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a most recent common ancestor with Asian elephants
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about six million years ago,
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so slightly closer to the Asian elephant.
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With advances in ancient DNA technology,
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we can actually now start to begin to sequence
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the genomes of those other extinct mammoth forms that I mentioned,
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and I just wanted to talk about two of them,
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the woolly and the Columbian mammoth,
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both of which were living very close to each other
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during glacial peaks,
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so when the glaciers were massive in North America,
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the woollies were pushed into these subglacial ecotones,
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and came into contact with the relatives living to the south,
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and there they shared refugia,
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and a little bit more than the refugia, it turns out.
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It looks like they were interbreeding.
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And that this is not an uncommon feature
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in Proboscideans, because it turns out
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that large savanna male elephants will outcompete
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the smaller forest elephants for their females.
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So large, hairless Columbians
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outcompeting the smaller male woollies.
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It reminds me a bit of high school, unfortunately.
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(Laughter)
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So this is not trivial, given the idea that we want
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to revive extinct species, because it turns out
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that an African and an Asian elephant
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can actually interbreed and have live young,
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and this has actually occurred by accident in a zoo
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in Chester, U.K., in 1978.
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So that means that we can actually take Asian elephant chromosomes,
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modify them into all those positions we've actually now
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been able to discriminate with the mammoth genome,
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we can put that into an enucleated cell,
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differentiate that into a stem cell,
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subsequently differentiate that maybe into a sperm,
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artificially inseminate an Asian elephant egg,
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and over a long and arduous procedure,
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actually bring back something that looks like this.
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Now, this wouldn't be an exact replica,
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because the short DNA fragments that I told you about
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will prevent us from building the exact structure,
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but it would make something that looked and felt
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very much like a woolly mammoth did.
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Now, when I bring up this with my friends,
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we often talk about, well, where would you put it?
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Where are you going to house a mammoth?
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There's no climates or habitats suitable.
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Well, that's not actually the case.
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It turns out that there are swaths of habitat
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in the north of Siberia and Yukon
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that actually could house a mammoth.
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Remember, this was a highly plastic animal
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that lived over tremendous climate variation.
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So this landscape would be easily able to house it,
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and I have to admit that there [is] a part of the child in me,
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the boy in me, that would love to see
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these majestic creatures walk across the permafrost
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of the north once again, but I do have to admit
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that part of the adult in me sometimes wonders
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whether or not we should.
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Thank you very much.
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(Applause)
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Ryan Phelan: Don't go away.
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You've left us with a question.
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I'm sure everyone is asking this. When you say, "Should we?"
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it feels like you're reticent there,
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and yet you've given us a vision of it being so possible.
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What's your reticence?
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Hendrik Poinar: I don't think it's reticence.
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I think it's just that we have to think very deeply
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about the implications, ramifications of our actions,
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and so as long as we have good, deep discussion
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like we're having now, I think
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we can come to a very good solution as to why to do it.
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But I just want to make sure that we spend time
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thinking about why we're doing it first.
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RP: Perfect. Perfect answer. Thank you very much, Hendrik.
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HP: Thank you. (Applause)
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