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So this is a talk about gene drives,

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but I'm going to start
by telling you a brief story.

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20 years ago, a biologist
named Anthony James

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got obsessed with the idea
of making mosquitos

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that didn't transmit malaria.

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It was a great idea,
and pretty much a complete failure.

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For one thing, it turned out
to be really hard

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to make a malaria-resistant mosquito.

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James managed it, finally,
just a few years ago,

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by adding some genes
that make it impossible

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for the malaria parasite
to survive inside the mosquito.

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But that just created another problem.

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Now that you've got
a malaria-resistant mosquito,

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how do you get it to replace
all the malaria-carrying mosquitos?

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There are a couple options,

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but plan A was basically to breed up

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a bunch of the new
genetically-engineered mosquitos

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release them into the wild

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and hope that they pass on their genes.

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The problem was that you'd have to release

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literally 10 times the number
of native mosquitos to work.

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So in a village with 10,000 mosquitos,

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you release an extra 100,000.

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As you might guess,

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this was not a very popular strategy
with the villagers.

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(Laughter)

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Then, last January,
Anthony James got an email

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from a biologist named Ethan Bier.

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Bier said that he
and his grad student Valentino Gantz

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had stumbled on a tool
that could not only guarantee

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that a particular genetic trait
would be inherited,

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but that it would spread
incredibly quickly.

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If they were right,
it would basically solve the problem

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that he and James had been
working on for 20 years.

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As a test, they engineered two mosquitos
to carry the anti-malaria gene

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and also this new tool, a gene drive,

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which I'll explain in a minute.

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Finally, they set it up
so that any mosquitos

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that had inherited the anti-malaria gene

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wouldn't have the usual white eyes,
but would instead have red eyes.

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That was pretty much just for convenience

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so they could tell just at a glance
which was which.

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So they took their two
anti-malarial, red-eyed mosquitos

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and put them in a box
with 30 ordinary white-eyed ones,

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and let them breed.

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In two generations, those had produced
3,800 grandchildren.

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That is not the surprising part.

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This is the surprising part:

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given that you started
with just two red-eyed mosquitos

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and 30 white-eyed ones,

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you expect mostly white-eyed descendants.

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Instead, when James opened the box,

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all 3,800 mosquitos had red eyes.

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When I asked Ethan Bier about this moment,

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he became so excited that he was literally
shouting into the phone.

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That's because getting
only red-eyed mosquitos

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violates a rule that is the absolute
cornerstone of biology,

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Mendelian genetics.

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I'll keep this quick,

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but Mendelian genetics
says when a male and a female mate,

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their baby inherits half
of its DNA from each parent.

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So if our original mosquito was aa
and our new mosquito is aB,

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where B is the anti-malarial gene,

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the babies should come out
in four permutations:

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aa, aB, aa, Ba.

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Instead, with the new gene drive,

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they all came out aB.

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Biologically, that shouldn't
even be possible.

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So what happened?

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The first thing that happened

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was the arrival of a gene-editing tool
known as CRISPR in 2012.

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Many of you have probably
heard about CRISPR,

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so I'll just say briefly that CRISPR
is a tool that allows researchers

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to edit genes very precisely,
easily and quickly.

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It does this by harnessing a mechanism
that already existed in bacteria.

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Basically, there's a protein
that acts like a scissors

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and cuts the DNA,

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and there's an RNA molecule
that directs the scissors

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to any point on the genome you want.

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The result is basically
a word processor for genes.

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You can take an entire gene
out, put one in,

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or even edit just a single
letter within a gene.

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And you can do it in nearly any species.

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OK, remember how I said that gene drives
originally had two problems?

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The first was that it was hard
to engineer a mosquito

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to be malaria-resistant.

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That's basically gone now,
thanks to CRISPR.

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But the other problem was logistical.

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How do you get your trait to spread?

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This is where it gets clever.

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A couple years ago, a biologist
at Harvard named Kevin Esvelt

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wondered what would happen

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if you made it so that
CRISPR inserted not only your new gene

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but also the machinery
that does the cutting and pasting.

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In other words, what if CRISPR
also copied and pasted itself.

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You'd end up with a perpetual
motion machine for gene editing.

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And that's exactly what happened.

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This CRISPR gene drive that Esvelt created

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not only guarantees
that a trait will get passed on,

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but if it's used in the germline cells,

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it will automatically copy and paste
your new gene

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into both chromosomes
of every single individual.

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It's like a global search and replace,

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or in science terms, it makes
a heterozygous trait homozygous.

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So, what does this mean?

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For one thing, it means we have
a very powerful,

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but also somewhat alarming new tool.

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Up until now, the fact that gene drives
didn't work very well

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was actually kind of a relief.

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Normally when we mess around
with an organism's genes,

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we make that thing
less evolutionarily fit.

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So biologists can make
all the mutant fruit flies they want

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without worrying about it.

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If some escape, natural selection
just takes care of them.

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What's remarkable and powerful
and frightening about gene drives

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is that that will no longer be true.

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Assuming that your trait does not have
a big evolutionary handicap,

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like a mosquito that can't fly,

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the CRISPR-based gene drive
will spread the change relentlessly

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until it is in every single individual
in the population.

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Now, it isn't easy to make
a gene drive that works that well,

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but James and Esvelt think that we can.

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The good news is that this opens
the door to some remarkable things.

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If you put an anti-malarial gene drive

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in just 1 percent of Anopheles mosquitoes,

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the species that transmits malaria,

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researchers estimate that it would spread
to the entire population in a year.

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So in a year, you could virtually
eliminate malaria.

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In practice, we're still a few years out
from being able to do that,

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but still, a 1,000 children
a day die of malaria.

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In a year, that number
could be almost zero.

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The same goes for dengue fever,
chikungunya, yellow fever.

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And it gets better.

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Say you want to get rid
of an invasive species,

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like get Asian carp
out of the Great Lakes.

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All you have to do is release a gene drive

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that makes the fish produce
only male offspring.

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In a few generations,
there'll be no females left, no more carp.

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In theory, this means we could restore
hundreds of native species

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that have been pushed to the brink.

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OK, that's the good news,

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this is the bad news.

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Gene drives are so effective

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that even an accidental release
could change an entire species,

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and often very quickly.

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Anthony James took good precautions.

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He bred his mosquitos
in a bio-containment lab

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and he also used a species
that's not native to the US

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so that even if some did escape,

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they'd just die off, there'd be nothing
for them to mate with.

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But it's also true that if a dozen
Asian carp with the all-male gene drive

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accidentally got carried
from the Great Lakes back to Asia,

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they could potentially wipe out
the native Asian carp population.

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And that's not so unlikely,
given how connected our world is.

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In fact, it's why we have
an invasive species problem.

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And that's fish.

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Things like mosquitos and fruit flies,

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there's literally no way to contain them.

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They cross borders
and oceans all the time.

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OK, the other piece of bad news

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is that a gene drive
might not stay confined

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to what we call the target species.

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That's because of gene flow,

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which is a fancy way of saying
that neighboring species

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sometimes interbreed.

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If that happens, it's possible
a gene drive could cross over,

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like Asian carp could infect
some other kind of carp.

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That's not so bad if your drive
just promotes a trait, like eye color.

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In fact, there's a decent
chance that we'll see

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a wave of very weird fruit flies
in the near future.

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But it could be a disaster

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if your drive is deigned
to eliminate the species entirely.

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The last worrisome thing
is that the technology to do this,

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to genetically engineer an organism
and include a gene drive,

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is something that basically any lab
in the world can do.

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An undergraduate can do it.

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A talented high schooler
with some equipment can do it.

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Now, I'm guessing
that this sounds terrifying.

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(Laughter)

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Interestingly though,
nearly every scientist I talk to

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seemed to think that gene drives were not
actually that frightening or dangerous.

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Partly because they believe
that scientists will be

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very cautious and responsible
about using them.

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(Laughter)

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So far, that's been true.

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But gene drives also have
some actual limitations.

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So for one thing, they work
only in sexually reproducing species.

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So thank goodness, they can't be used
to engineer viruses or bacteria.

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Also, the trait spreads
only with each successive generation.

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So changing or eliminating a population

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is practical only if that species
has a fast reproductive cycle,

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like insects or maybe
small vertebrates like mice or fish.

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In elephants or people,
it would take centuries

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for a trait to spread
widely enough to matter.

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Also, even with CRISPR, it's not that easy
to engineer a truly devastating trait.

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Say you wanted to make a fruit fly

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that feeds on ordinary fruit
instead of rotting fruit,

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with the aim of sabotaging
American agriculture.

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First, you'd have to figure out

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which genes control
what the fly wants to eat,

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which is already a very long
and complicated project.

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Then you'd have to alter those genes
to change the fly's behavior

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to whatever you'd want it to be,

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which is an even longer
and more complicated project.

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And it might not even work,

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because the genes
that control behavior are complex.

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So if you're a terrorist
and have to choose

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between starting a grueling
basic research program

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that will require years of meticulous
lab work and still might not pan out,

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or just blowing stuff up?

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You'll probably choose the later.

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This is especially true
because at least in theory,

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it should be pretty easy
to build what's called a reversal drive.

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That's one that basically overwrites
the change made by the first gene drive.

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So if you don't like
the effects of a change,

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you can just release a second drive
that will cancel it out,

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at least in theory.

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OK, so where does this leave us?

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We now have the ability
to change entire species at will.

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Should we?

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Are we gods now?

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I'm not sure I'd say that.

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But I would say this:

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first, some very smart people

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are even now debating
how to regulate gene drives.

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At the same time,
some other very smart people

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are working hard to create safeguards,

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like gene drives that self-regulate
or peter out after a few generations.

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That's great.

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But this technology still requires
a conversation.

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And given the nature of gene drives,

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that conversation has to be global.

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What if Kenya wants to use a drive
but Tanzania doesn't?

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Who decides whether to release
a gene drive that can fly?

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I don't have the answer to that question.

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All we can do going forward, I think,

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is talk honestly
about the risks and benefits

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and take responsibility for our choices.

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By that I mean, not just the choice
to use a gene drive,

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but also the choice not to use one.

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Humans have a tendency to assume
that the safest option

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is to preserve the status quo.

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But that's not always the case.

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Gene drives have risks,
and those need to be discussed,

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but malaria exists now
and kills 1,000 people a day.

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To combat it, we spray pesticides
that do grave damage to other species,

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including amphibians and birds.

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So when you hear about gene drives
in the coming months,

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and trust me, you will
be hearing about them,

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remember that.

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It can be frightening to act,

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but sometimes, not acting is worse.

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(Applause)