ABOUT THE SPEAKER
Jennifer Kahn - Science journalist
In articles that span the gene-editing abilities of CRISPR, the roots of psychopathic behavior in children, and much more, Jennifer Kahn weaves gripping stories from unlikely sources.

Why you should listen

Jennifer Kahn likes to seek out complex stories, with the goal of illuminating their nuances. She teaches in the magazine program at the UC Berkeley Graduate School of Journalism, and is a contributing writer for the New York Times Magazine; she has written features and cover stories for The New Yorker, National Geographic, Outside, Wired and many more.

Her work has appeared in the Best American Science Writing anthology series four times, most recently for the New Yorker story “A Cloud of Smoke,” a story on the complicated death of a policeman after 9/11.

More profile about the speaker
Jennifer Kahn | Speaker | TED.com
TED2016

Jennifer Kahn: Gene editing can now change an entire species -- forever

Filmed:
1,922,129 views

CRISPR gene drives allow scientists to change sequences of DNA and guarantee that the resulting edited genetic trait is inherited by future generations, opening up the possibility of altering entire species forever. More than anything, the technology has led to questions: How will this new power affect humanity? What are we going to use it to change? Are we gods now? Join journalist Jennifer Kahn as she ponders these questions and shares a potentially powerful application of gene drives: the development of disease-resistant mosquitoes that could knock out malaria and Zika.
- Science journalist
In articles that span the gene-editing abilities of CRISPR, the roots of psychopathic behavior in children, and much more, Jennifer Kahn weaves gripping stories from unlikely sources. Full bio

Double-click the English transcript below to play the video.

00:12
So this is a talk about gene drives,
0
844
2462
00:15
but I'm going to start
by telling you a brief story.
1
3330
2553
00:18
20 years ago, a biologist
named Anthony James
2
6621
3223
00:21
got obsessed with the idea
of making mosquitos
3
9868
2319
00:24
that didn't transmit malaria.
4
12211
2579
00:27
It was a great idea,
and pretty much a complete failure.
5
15683
4056
00:32
For one thing, it turned out
to be really hard
6
20596
2660
00:35
to make a malaria-resistant mosquito.
7
23280
2007
00:38
James managed it, finally,
just a few years ago,
8
26286
3627
00:41
by adding some genes
that make it impossible
9
29937
2071
00:44
for the malaria parasite
to survive inside the mosquito.
10
32032
2714
00:47
But that just created another problem.
11
35551
1822
00:50
Now that you've got
a malaria-resistant mosquito,
12
38043
2842
00:52
how do you get it to replace
all the malaria-carrying mosquitos?
13
40909
3586
00:58
There are a couple options,
14
46107
1473
00:59
but plan A was basically to breed up
15
47604
2023
01:01
a bunch of the new
genetically-engineered mosquitos
16
49651
3087
01:04
release them into the wild
17
52762
1326
01:06
and hope that they pass on their genes.
18
54112
1967
01:08
The problem was that you'd have to release
19
56673
2114
01:10
literally 10 times the number
of native mosquitos to work.
20
58811
4300
01:15
So in a village with 10,000 mosquitos,
21
63135
2087
01:17
you release an extra 100,000.
22
65246
2079
01:20
As you might guess,
23
68229
1150
01:21
this was not a very popular strategy
with the villagers.
24
69403
2754
01:24
(Laughter)
25
72181
1150
01:26
Then, last January,
Anthony James got an email
26
74963
3704
01:30
from a biologist named Ethan Bier.
27
78691
1951
01:33
Bier said that he
and his grad student Valentino Gantz
28
81400
2859
01:36
had stumbled on a tool
that could not only guarantee
29
84283
2944
01:39
that a particular genetic trait
would be inherited,
30
87251
2674
01:41
but that it would spread
incredibly quickly.
31
89949
2079
01:44
If they were right,
it would basically solve the problem
32
92734
2666
01:47
that he and James had been
working on for 20 years.
33
95424
2381
01:50
As a test, they engineered two mosquitos
to carry the anti-malaria gene
34
98450
4658
01:55
and also this new tool, a gene drive,
35
103132
2159
01:57
which I'll explain in a minute.
36
105315
1491
01:59
Finally, they set it up
so that any mosquitos
37
107506
2333
02:01
that had inherited the anti-malaria gene
38
109863
1938
02:03
wouldn't have the usual white eyes,
but would instead have red eyes.
39
111825
3999
02:08
That was pretty much just for convenience
40
116682
2050
02:10
so they could tell just at a glance
which was which.
41
118756
2537
02:14
So they took their two
anti-malarial, red-eyed mosquitos
42
122192
2757
02:16
and put them in a box
with 30 ordinary white-eyed ones,
43
124973
2659
02:19
and let them breed.
44
127656
1174
02:21
In two generations, those had produced
3,800 grandchildren.
45
129383
3857
02:26
That is not the surprising part.
46
134217
1793
02:28
This is the surprising part:
47
136716
1922
02:30
given that you started
with just two red-eyed mosquitos
48
138662
2907
02:33
and 30 white-eyed ones,
49
141593
1334
02:34
you expect mostly white-eyed descendants.
50
142951
2761
02:38
Instead, when James opened the box,
51
146514
3024
02:41
all 3,800 mosquitos had red eyes.
52
149562
3341
02:45
When I asked Ethan Bier about this moment,
53
153315
2040
02:47
he became so excited that he was literally
shouting into the phone.
54
155379
3515
02:51
That's because getting
only red-eyed mosquitos
55
159886
2163
02:54
violates a rule that is the absolute
cornerstone of biology,
56
162073
2948
02:57
Mendelian genetics.
57
165045
1242
02:58
I'll keep this quick,
58
166912
1169
03:00
but Mendelian genetics
says when a male and a female mate,
59
168105
2764
03:02
their baby inherits half
of its DNA from each parent.
60
170893
2642
03:05
So if our original mosquito was aa
and our new mosquito is aB,
61
173559
3595
03:09
where B is the anti-malarial gene,
62
177178
1802
03:11
the babies should come out
in four permutations:
63
179004
2387
03:13
aa, aB, aa, Ba.
64
181415
2573
03:16
Instead, with the new gene drive,
65
184884
2289
03:19
they all came out aB.
66
187197
1512
03:21
Biologically, that shouldn't
even be possible.
67
189900
2552
03:24
So what happened?
68
192476
1304
03:26
The first thing that happened
69
194709
1444
03:28
was the arrival of a gene-editing tool
known as CRISPR in 2012.
70
196177
3270
03:32
Many of you have probably
heard about CRISPR,
71
200701
2110
03:34
so I'll just say briefly that CRISPR
is a tool that allows researchers
72
202835
3301
03:38
to edit genes very precisely,
easily and quickly.
73
206160
2579
03:41
It does this by harnessing a mechanism
that already existed in bacteria.
74
209533
3729
03:45
Basically, there's a protein
that acts like a scissors
75
213286
2626
03:47
and cuts the DNA,
76
215936
1234
03:49
and there's an RNA molecule
that directs the scissors
77
217194
2483
03:51
to any point on the genome you want.
78
219701
1718
03:53
The result is basically
a word processor for genes.
79
221443
2690
03:56
You can take an entire gene
out, put one in,
80
224157
2626
03:58
or even edit just a single
letter within a gene.
81
226807
2445
04:01
And you can do it in nearly any species.
82
229646
1953
04:05
OK, remember how I said that gene drives
originally had two problems?
83
233328
3714
04:09
The first was that it was hard
to engineer a mosquito
84
237835
3120
04:12
to be malaria-resistant.
85
240979
1387
04:14
That's basically gone now,
thanks to CRISPR.
86
242390
2127
04:17
But the other problem was logistical.
87
245117
1762
04:19
How do you get your trait to spread?
88
247307
1802
04:22
This is where it gets clever.
89
250196
1476
04:24
A couple years ago, a biologist
at Harvard named Kevin Esvelt
90
252943
3602
04:28
wondered what would happen
91
256569
1350
04:29
if you made it so that
CRISPR inserted not only your new gene
92
257943
3627
04:33
but also the machinery
that does the cutting and pasting.
93
261594
2841
04:37
In other words, what if CRISPR
also copied and pasted itself.
94
265233
3840
04:42
You'd end up with a perpetual
motion machine for gene editing.
95
270145
3131
04:46
And that's exactly what happened.
96
274458
1734
04:49
This CRISPR gene drive that Esvelt created
97
277037
2878
04:51
not only guarantees
that a trait will get passed on,
98
279939
3643
04:55
but if it's used in the germline cells,
99
283606
2438
04:58
it will automatically copy and paste
your new gene
100
286068
2576
05:00
into both chromosomes
of every single individual.
101
288668
2646
05:03
It's like a global search and replace,
102
291743
2397
05:06
or in science terms, it makes
a heterozygous trait homozygous.
103
294164
3221
05:11
So, what does this mean?
104
299045
2611
05:13
For one thing, it means we have
a very powerful,
105
301680
2724
05:16
but also somewhat alarming new tool.
106
304428
2657
05:20
Up until now, the fact that gene drives
didn't work very well
107
308576
2889
05:23
was actually kind of a relief.
108
311489
1483
05:25
Normally when we mess around
with an organism's genes,
109
313425
2682
05:28
we make that thing
less evolutionarily fit.
110
316131
2349
05:30
So biologists can make
all the mutant fruit flies they want
111
318504
2833
05:33
without worrying about it.
112
321361
1253
05:34
If some escape, natural selection
just takes care of them.
113
322638
3007
05:38
What's remarkable and powerful
and frightening about gene drives
114
326750
3223
05:41
is that that will no longer be true.
115
329997
1760
05:45
Assuming that your trait does not have
a big evolutionary handicap,
116
333092
3564
05:48
like a mosquito that can't fly,
117
336680
2079
05:50
the CRISPR-based gene drive
will spread the change relentlessly
118
338783
3453
05:54
until it is in every single individual
in the population.
119
342260
3006
05:59
Now, it isn't easy to make
a gene drive that works that well,
120
347101
2889
06:02
but James and Esvelt think that we can.
121
350014
2174
06:05
The good news is that this opens
the door to some remarkable things.
122
353339
3824
06:09
If you put an anti-malarial gene drive
123
357187
1904
06:11
in just 1 percent of Anopheles mosquitoes,
124
359115
2200
06:13
the species that transmits malaria,
125
361339
1752
06:15
researchers estimate that it would spread
to the entire population in a year.
126
363488
4119
06:20
So in a year, you could virtually
eliminate malaria.
127
368178
2869
06:23
In practice, we're still a few years out
from being able to do that,
128
371455
3872
06:27
but still, a 1,000 children
a day die of malaria.
129
375351
2718
06:30
In a year, that number
could be almost zero.
130
378093
2190
06:32
The same goes for dengue fever,
chikungunya, yellow fever.
131
380966
2896
06:37
And it gets better.
132
385211
1405
06:39
Say you want to get rid
of an invasive species,
133
387215
2476
06:41
like get Asian carp
out of the Great Lakes.
134
389715
2123
06:44
All you have to do is release a gene drive
135
392434
2024
06:46
that makes the fish produce
only male offspring.
136
394482
2317
06:49
In a few generations,
there'll be no females left, no more carp.
137
397386
4198
06:53
In theory, this means we could restore
hundreds of native species
138
401608
3079
06:56
that have been pushed to the brink.
139
404711
1667
06:59
OK, that's the good news,
140
407410
3287
07:02
this is the bad news.
141
410721
1292
07:05
Gene drives are so effective
142
413070
2028
07:07
that even an accidental release
could change an entire species,
143
415122
3825
07:10
and often very quickly.
144
418971
1190
07:13
Anthony James took good precautions.
145
421178
2126
07:15
He bred his mosquitos
in a bio-containment lab
146
423328
2166
07:17
and he also used a species
that's not native to the US
147
425518
2588
07:20
so that even if some did escape,
148
428130
1555
07:21
they'd just die off, there'd be nothing
for them to mate with.
149
429709
3015
07:24
But it's also true that if a dozen
Asian carp with the all-male gene drive
150
432748
4023
07:28
accidentally got carried
from the Great Lakes back to Asia,
151
436795
3929
07:32
they could potentially wipe out
the native Asian carp population.
152
440748
3429
07:37
And that's not so unlikely,
given how connected our world is.
153
445930
2912
07:40
In fact, it's why we have
an invasive species problem.
154
448866
2571
07:43
And that's fish.
155
451912
1168
07:45
Things like mosquitos and fruit flies,
156
453428
2588
07:48
there's literally no way to contain them.
157
456040
1960
07:50
They cross borders
and oceans all the time.
158
458024
2111
07:53
OK, the other piece of bad news
159
461754
2182
07:55
is that a gene drive
might not stay confined
160
463960
2318
07:58
to what we call the target species.
161
466302
1813
08:00
That's because of gene flow,
162
468556
1499
08:02
which is a fancy way of saying
that neighboring species
163
470079
2597
08:04
sometimes interbreed.
164
472700
1248
08:05
If that happens, it's possible
a gene drive could cross over,
165
473972
3151
08:09
like Asian carp could infect
some other kind of carp.
166
477147
2527
08:11
That's not so bad if your drive
just promotes a trait, like eye color.
167
479698
3715
08:15
In fact, there's a decent
chance that we'll see
168
483437
2247
08:17
a wave of very weird fruit flies
in the near future.
169
485708
2571
08:21
But it could be a disaster
170
489390
1263
08:22
if your drive is deigned
to eliminate the species entirely.
171
490677
2904
08:26
The last worrisome thing
is that the technology to do this,
172
494351
3528
08:29
to genetically engineer an organism
and include a gene drive,
173
497903
3691
08:33
is something that basically any lab
in the world can do.
174
501618
3334
08:36
An undergraduate can do it.
175
504976
1340
08:39
A talented high schooler
with some equipment can do it.
176
507209
3282
08:44
Now, I'm guessing
that this sounds terrifying.
177
512526
2309
08:47
(Laughter)
178
515351
2206
08:49
Interestingly though,
nearly every scientist I talk to
179
517581
2890
08:52
seemed to think that gene drives were not
actually that frightening or dangerous.
180
520495
3881
08:56
Partly because they believe
that scientists will be
181
524400
2628
08:59
very cautious and responsible
about using them.
182
527052
2204
09:01
(Laughter)
183
529280
1014
09:02
So far, that's been true.
184
530318
1230
09:04
But gene drives also have
some actual limitations.
185
532302
2696
09:07
So for one thing, they work
only in sexually reproducing species.
186
535022
3309
09:10
So thank goodness, they can't be used
to engineer viruses or bacteria.
187
538704
3428
09:14
Also, the trait spreads
only with each successive generation.
188
542156
3190
09:17
So changing or eliminating a population
189
545370
1993
09:19
is practical only if that species
has a fast reproductive cycle,
190
547387
3326
09:22
like insects or maybe
small vertebrates like mice or fish.
191
550737
2800
09:26
In elephants or people,
it would take centuries
192
554438
2261
09:28
for a trait to spread
widely enough to matter.
193
556723
2380
09:32
Also, even with CRISPR, it's not that easy
to engineer a truly devastating trait.
194
560079
5142
09:38
Say you wanted to make a fruit fly
195
566079
1729
09:39
that feeds on ordinary fruit
instead of rotting fruit,
196
567832
2555
09:42
with the aim of sabotaging
American agriculture.
197
570411
2633
09:45
First, you'd have to figure out
198
573068
1530
09:46
which genes control
what the fly wants to eat,
199
574622
2772
09:49
which is already a very long
and complicated project.
200
577418
2547
09:52
Then you'd have to alter those genes
to change the fly's behavior
201
580489
3304
09:55
to whatever you'd want it to be,
202
583817
1538
09:57
which is an even longer
and more complicated project.
203
585379
2801
10:00
And it might not even work,
204
588204
1318
10:01
because the genes
that control behavior are complex.
205
589546
2494
10:04
So if you're a terrorist
and have to choose
206
592064
2008
10:06
between starting a grueling
basic research program
207
594096
2358
10:08
that will require years of meticulous
lab work and still might not pan out,
208
596478
3527
10:12
or just blowing stuff up?
209
600029
1347
10:13
You'll probably choose the later.
210
601400
1655
10:15
This is especially true
because at least in theory,
211
603498
2420
10:17
it should be pretty easy
to build what's called a reversal drive.
212
605942
3134
10:21
That's one that basically overwrites
the change made by the first gene drive.
213
609100
3698
10:24
So if you don't like
the effects of a change,
214
612822
2294
10:27
you can just release a second drive
that will cancel it out,
215
615140
2833
10:29
at least in theory.
216
617997
1150
10:33
OK, so where does this leave us?
217
621374
1722
10:36
We now have the ability
to change entire species at will.
218
624604
3595
10:41
Should we?
219
629017
1166
10:42
Are we gods now?
220
630552
1365
10:45
I'm not sure I'd say that.
221
633972
1333
10:48
But I would say this:
222
636094
1227
10:50
first, some very smart people
223
638329
1858
10:52
are even now debating
how to regulate gene drives.
224
640211
2856
10:55
At the same time,
some other very smart people
225
643598
2564
10:58
are working hard to create safeguards,
226
646186
2111
11:00
like gene drives that self-regulate
or peter out after a few generations.
227
648321
3552
11:04
That's great.
228
652644
1200
11:06
But this technology still requires
a conversation.
229
654313
2547
11:10
And given the nature of gene drives,
230
658059
1730
11:11
that conversation has to be global.
231
659813
1690
11:14
What if Kenya wants to use a drive
but Tanzania doesn't?
232
662131
2707
11:17
Who decides whether to release
a gene drive that can fly?
233
665241
3367
11:22
I don't have the answer to that question.
234
670874
1954
11:25
All we can do going forward, I think,
235
673618
2008
11:27
is talk honestly
about the risks and benefits
236
675650
2834
11:30
and take responsibility for our choices.
237
678508
2222
11:33
By that I mean, not just the choice
to use a gene drive,
238
681817
3913
11:37
but also the choice not to use one.
239
685754
1999
11:41
Humans have a tendency to assume
that the safest option
240
689111
2977
11:44
is to preserve the status quo.
241
692112
1792
11:46
But that's not always the case.
242
694905
1572
11:49
Gene drives have risks,
and those need to be discussed,
243
697711
3401
11:53
but malaria exists now
and kills 1,000 people a day.
244
701136
3150
11:56
To combat it, we spray pesticides
that do grave damage to other species,
245
704977
3564
12:00
including amphibians and birds.
246
708565
1570
12:03
So when you hear about gene drives
in the coming months,
247
711668
2864
12:06
and trust me, you will
be hearing about them,
248
714556
2254
12:08
remember that.
249
716834
1544
12:10
It can be frightening to act,
250
718402
2020
12:12
but sometimes, not acting is worse.
251
720446
2137
12:16
(Applause)
252
724746
7820

▲Back to top

ABOUT THE SPEAKER
Jennifer Kahn - Science journalist
In articles that span the gene-editing abilities of CRISPR, the roots of psychopathic behavior in children, and much more, Jennifer Kahn weaves gripping stories from unlikely sources.

Why you should listen

Jennifer Kahn likes to seek out complex stories, with the goal of illuminating their nuances. She teaches in the magazine program at the UC Berkeley Graduate School of Journalism, and is a contributing writer for the New York Times Magazine; she has written features and cover stories for The New Yorker, National Geographic, Outside, Wired and many more.

Her work has appeared in the Best American Science Writing anthology series four times, most recently for the New Yorker story “A Cloud of Smoke,” a story on the complicated death of a policeman after 9/11.

More profile about the speaker
Jennifer Kahn | Speaker | TED.com