Is human evolution speeding up or slowing down? - Laurence Hurst
-
0:07 - 0:13The Tibetan high plateau lies
about 4500 meters above sea level, -
0:13 - 0:17with only 60% of the oxygen found below.
-
0:17 - 0:21While visitors and recent settlers
struggle with altitude sickness, -
0:21 - 0:25native Tibetans sprint up mountains.
-
0:25 - 0:28This ability comes not from training
or practice, -
0:28 - 0:32but from changes to a few genes
that allow their bodies -
0:32 - 0:35to make the most of limited oxygen.
-
0:35 - 0:38These differences are apparent from birth—
-
0:38 - 0:42Tibetan babies have, on average,
higher birth weights, -
0:42 - 0:44higher oxygen saturation,
-
0:44 - 0:49and are much likelier to survive than
other babies born in this environment. -
0:49 - 0:53These genetic changes are estimated
to have evolved -
0:53 - 0:57over the last 3,000 years or so,
and are ongoing. -
0:57 - 0:59That may sound like a long time,
-
0:59 - 1:06but would be the fastest an adaptation
has ever evolved in a human population. -
1:06 - 1:09It’s clear that human evolution
isn’t over— -
1:09 - 1:11so what are other recent changes?
-
1:11 - 1:17And will our technological and scientific
innovations impact our evolution? -
1:17 - 1:18In the past few thousand years,
-
1:18 - 1:23many populations have evolved genetic
adaptations to their local environments. -
1:23 - 1:30People in Siberia and the high arctic are
uniquely adapted to survive extreme cold. -
1:30 - 1:32They’re slower to develop frostbite,
-
1:32 - 1:36and can continue to use their hands
in subzero temperatures -
1:36 - 1:39much longer than most people.
-
1:39 - 1:42They’ve undergone selection
for a higher metabolic rate -
1:42 - 1:45that increases heat production.
-
1:45 - 1:50Further south, the Bajau people
of southeast Asia can dive 70 meters -
1:50 - 1:54and stay underwater
for almost fifteen minutes. -
1:54 - 1:58Over thousands of years living
as nomadic hunters at sea, -
1:58 - 2:05they have genetically-hardwired unusually
large spleens that act as oxygen stores, -
2:05 - 2:09enabling them to stay underwater
for longer— -
2:09 - 2:13an adaptation similar
to that of deep diving seals. -
2:13 - 2:16Though it may seem pedestrian
by comparison, -
2:16 - 2:20the ability to drink milk
is another such adaptation. -
2:20 - 2:23All mammals can drink
their mother’s milk as babies. -
2:23 - 2:28After weaning they switch off the gene
that allows them to digest milk. -
2:28 - 2:33But communities in sub-Saharan Africa,
the middle east and northwest Europe -
2:33 - 2:38that used cows for milk have seen
a rapid increase in DNA variants -
2:38 - 2:44that prevent the gene from switching off
over the last 7 to 8000 years. -
2:44 - 2:49At least in Europe, milk drinking may
have given people a source of calcium -
2:49 - 2:53to aid in vitamin D production,
as they moved north and sunlight, -
2:53 - 2:57the usual source of vitamin D,
decreased. -
2:57 - 2:59Though not always in obvious ways,
-
2:59 - 3:04all of these changes improve people’s
chance of surviving to reproductive age— -
3:04 - 3:06that’s what drives natural selection,
-
3:06 - 3:10the force behind all these
evolutionary changes. -
3:10 - 3:14Modern medicine removes
many of these selective pressures -
3:14 - 3:16by keeping us alive when our genes,
-
3:16 - 3:19sometimes combined
with infectious diseases, -
3:19 - 3:21would have killed us.
-
3:21 - 3:25Antibiotics, vaccines, clean water
and good sanitation -
3:25 - 3:29all make differences between our genes
less important. -
3:29 - 3:32Similarly, our ability to cure
childhood cancers, -
3:32 - 3:37surgically extract inflamed appendixes,
and deliver babies -
3:37 - 3:41whose mothers have life-threatening
pregnancy-specific conditions, -
3:41 - 3:46all tend to stop selection by allowing
more people to survive -
3:46 - 3:48to a reproductive age.
-
3:48 - 3:52But even if every person on Earth
has access to modern medicine, -
3:52 - 3:55it won’t spell the end of human evolution.
-
3:55 - 4:00That’s because there are other aspects
of evolution besides natural selection. -
4:00 - 4:02Modern medicine makes genetic variation
-
4:02 - 4:06that would have been subject
to natural selection -
4:06 - 4:10subject to what’s called
genetic drift instead. -
4:10 - 4:15With genetic drift, genetic differences
vary randomly within a population. -
4:15 - 4:20On a genetic level, modern medicine
might actually increase variety, -
4:20 - 4:24because harmful mutations don’t kill
people and thus aren’t eliminated. -
4:24 - 4:29This variation doesn’t necessarily
translate to observable, or phenotypic, -
4:29 - 4:33differences among people, however.
-
4:33 - 4:36Researchers have also been investigating
whether genetic adaptations -
4:36 - 4:40to a specific environment
could appear very quickly -
4:40 - 4:44through epigenetic modification:
changes not to genes themselves, -
4:44 - 4:49but to whether and when certain genes
are expressed. -
4:49 - 4:51These changes can happen
during a lifetime, -
4:51 - 4:54and may even be passed to offspring—
-
4:54 - 4:59but so far researchers are conflicted
over whether epigenetic modifications -
4:59 - 5:02can really persist over many generations
-
5:02 - 5:07and lead to lasting changes
in populations. -
5:07 - 5:10There may also be other contributors
to human evolution. -
5:10 - 5:13Modern medicine and technology
are very new, -
5:13 - 5:17even compared to the quickest,
most recent changes by natural selection— -
5:17 - 5:22so only time can tell how our present
will shape our future.
- Title:
- Is human evolution speeding up or slowing down? - Laurence Hurst
- Speaker:
- Laurence Hurst
- Description:
-
View full lesson: https://ed.ted.com/lessons/is-human-evolution-speeding-up-or-slowing-down-laurence-hurst
In the past 3,000 years, many populations have evolved genetic adaptations to their local environments. People in Siberia and the high arctic are uniquely adapted to survive extreme cold. The Bajau people can dive 70 meters and stay underwater for almost 15 minutes. So what are other recent changes? And will our technological innovations impact our evolution? Laurence Hurst investigates.
Lesson by Laurence Hurst, directed by Philip Piaget & Rikke Planeta.
- Video Language:
- English
- Team:
- closed TED
- Project:
- TED-Ed
- Duration:
- 05:25
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