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TED2009

Nina Jablonski: Skin color is an illusion

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Nina Jablonski says that differing skin colors are simply our bodies' adaptation to varied climates and levels of UV exposure. Charles Darwin disagreed with this theory, but she explains, that's because he did not have access to NASA.

- Anthropologist
Nina Jablonski is author of Skin: A Natural History, a close look at human skin’s many remarkable traits: its colors, its sweatiness, the fact that we decorate it. Full bio

Interestingly, Charles Darwin
00:18
was born a very lightly pigmented man,
00:22
in a moderately-to-darkly pigmented world.
00:26
Over the course of his life,
00:30
Darwin had great privilege.
00:33
He lived in a fairly wealthy home.
00:35
He was raised by very supportive and interested parents.
00:38
And when he was in his 20s
00:42
he embarked upon a remarkable voyage on the ship the Beagle.
00:44
And during the course of that voyage,
00:48
he saw remarkable things:
00:51
tremendous diversity of plants and animals, and humans.
00:53
And the observations that he made
00:57
on that epic journey
00:59
were to be eventually distilled
01:01
into his wonderful book, "On the Origin of Species,"
01:03
published 150 years ago.
01:05
Now what is so interesting
01:09
and to some, the extent, what's a bit infamous
01:11
about "The Origin of Species,"
01:15
is that there is only one line in it
01:17
about human evolution.
01:19
"Light will be thrown on the origin of man
01:22
and his history."
01:25
It wasn't until much longer,
01:27
much later,
01:29
that Darwin actually spoke
01:31
and wrote about humans.
01:33
Now in his years of
01:36
traveling on the Beagle,
01:38
and from listening to the accounts
01:40
or explorers and naturalists,
01:42
he knew that skin color
01:44
was one of the most important ways
01:48
in which people varied.
01:50
And he was somewhat interested in the pattern of skin color.
01:52
He knew that darkly pigmented peoples
01:56
were found close to the equator;
01:58
lightly pigmented peoples, like himself,
02:01
were found closer to the poles.
02:03
So what did he make of all this?
02:06
Well he didn't write anything about it in The Origin of Species.
02:08
But much later, in 1871,
02:11
he did have something to say about it.
02:14
And it was quite curious. He said,
02:16
"Of all the differences between the races of men,
02:18
the color of the skin is the most conspicuous
02:21
and one of the best marked."
02:23
And he went on to say,
02:25
"These differences do not coincide
02:27
with corresponding differences in climate."
02:30
So he had traveled all around.
02:33
He had seen people of different colors
02:35
living in different places.
02:38
And yet he rejected the idea
02:40
that human skin pigmentation
02:42
was related to the climate.
02:45
If only Darwin lived today.
02:48
If only Darwin had NASA.
02:51
Now, one of the wonderful things that NASA does
02:54
is it puts up a variety of satellites
02:58
that detect all sort of interesting things about our environment.
03:00
And for many decades now
03:03
there have been a series of TOMS satellites
03:06
that have collected data about the radiation of the Earth's surface.
03:09
The TOMS 7 satellite data, shown here,
03:12
show the annual average
03:16
ultraviolet radiation at the Earth's surface.
03:18
Now the really hot pink and red areas
03:21
are those parts of the world that receive the highest amounts
03:24
of UV during the year.
03:27
The incrementally cooler colors --
03:30
blues, greens, yellows, and finally grays --
03:33
indicate areas of much lower ultraviolet radiation.
03:36
What's significant to the story of human skin pigmentation
03:39
is just how much of the Northern Hemisphere
03:43
is in these cool gray zones.
03:47
This has tremendous implications for our understanding
03:50
of the evolution of human skin pigmentation.
03:53
And what Darwin could not appreciate,
03:56
or didn't perhaps want to appreciate at the time,
03:59
is that there was a fundamental relationship
04:02
between the intensity of ultraviolet radiation
04:05
and skin pigmentation.
04:08
And that skin pigmentation itself
04:10
was a product of evolution.
04:13
And so when we look at a map of skin color,
04:16
and predicted skin color, as we know it today,
04:19
what we see is a beautiful gradient
04:22
from the darkest skin pigmentations toward the equator,
04:25
and the lightest ones toward the poles.
04:28
What's very, very important here
04:31
is that the earliest humans
04:35
evolved in high-UV environments,
04:37
in equatorial Africa.
04:40
The earliest members of our lineage,
04:42
the genus Homo, were darkly pigmented.
04:45
And we all share this incredible heritage
04:48
of having originally been
04:52
darkly pigmented,
04:54
two million to one and half million years ago.
04:56
Now what happened in our history?
04:59
Let's first look at the relationship
05:04
of ultraviolet radiation to the Earth's surface.
05:06
In those early days of our evolution,
05:09
looking at the equator,
05:12
we were bombarded by high levels of ultraviolet radiation.
05:14
The UVC, the most energetic type,
05:17
was occluded by the Earth's atmosphere.
05:20
But UVB and UVA
05:23
especially, came in unimpeded.
05:25
UVB turns out to be incredibly important.
05:27
It's very destructive,
05:31
but it also catalyzes the production of vitamin D in the skin,
05:33
vitamin D being a molecule that we very much need
05:37
for our strong bones, the health of our immune system,
05:41
and myriad other important functions in our bodies.
05:45
So, living at the equator, we got
05:48
lots and lots of ultraviolet radiation
05:50
and the melanin --
05:53
this wonderful, complex, ancient polymer
05:56
compound in our skin --
06:00
served as a superb natural sunscreen.
06:02
This polymer is amazing
06:06
because it's present in so many different organisms.
06:08
Melanin, in various forms, has probably been on the Earth
06:11
a billion years,
06:13
and has been recruited over and over again
06:16
by evolution, as often happens.
06:18
Why change it if it works?
06:22
So melanin was recruited, in our lineage,
06:24
and specifically in our earliest ancestors
06:28
evolving in Africa,
06:31
to be a natural sunscreen.
06:33
Where it protected the body
06:35
against the degradations of ultraviolet radiation,
06:37
the destruction, or damage to DNA,
06:40
and the breakdown of a very important molecule called folate,
06:43
which helps to fuel cell production,
06:47
and reproduction in the body.
06:50
So, it's wonderful. We evolved this very protective,
06:53
wonderful covering of melanin.
06:56
But then we moved.
06:59
And humans dispersed -- not once, but twice.
07:03
Major moves, outside of our equatorial homeland,
07:07
from Africa into other parts of the Old World,
07:11
and most recently, into the New World.
07:15
When humans dispersed into these latitudes,
07:17
what did they face?
07:20
Conditions were significantly colder,
07:22
but they were also less intense
07:25
with respect to the ultraviolet regime.
07:27
So if we're somewhere in the Northern Hemisphere,
07:29
look at what's happening to the ultraviolet radiation.
07:33
We're still getting a dose of UVA.
07:36
But all of the UVB,
07:39
or nearly all of it,
07:41
is dissipated through the thickness of the atmosphere.
07:43
In the winter, when you are skiing in the Alps,
07:46
you may experience ultraviolet radiation.
07:50
But it's all UVA,
07:53
and, significantly, that UVA
07:55
has no ability to make vitamin D in your skin.
07:57
So people inhabiting northern hemispheric environments
08:02
were bereft of the potential
08:07
to make vitamin D in their skin for most of the year.
08:10
This had tremendous consequences
08:13
for the evolution of human skin pigmentation.
08:16
Because what happened, in order to ensure health and well-being,
08:18
these lineages of people
08:23
dispersing into the Northern Hemisphere
08:25
lost their pigmentation.
08:29
There was natural selection
08:31
for the evolution of lightly pigmented skin.
08:33
Here we begin to see the evolution
08:38
of the beautiful sepia rainbow
08:40
that now characterizes all of humanity.
08:42
Lightly pigmented skin evolved not just once,
08:45
not just twice, but probably three times.
08:49
Not just in modern humans,
08:52
but in one of our distant unrelated ancestors,
08:54
the Neanderthals.
08:58
A remarkable, remarkable testament
09:00
to the power of evolution.
09:02
Humans have been on the move for a long time.
09:04
And just in the last 5,000 years,
09:07
in increasing rates, over increasing distances.
09:09
Here are just some of the biggest movements of people,
09:12
voluntary movements, in the last 5,000 years.
09:16
Look at some of the major latitudinal transgressions:
09:19
people from high UV areas
09:22
going to low UV and vice versa.
09:24
And not all these moves were voluntary.
09:27
Between 1520 and 1867,
09:31
12 million, 500 people
09:34
were moved from high UV
09:38
to low UV areas
09:40
in the transatlantic slave trade.
09:42
Now this had all sorts of invidious social consequences.
09:45
But it also had deleterious
09:49
health consequences to people.
09:52
So what? We've been on the move.
09:54
We're so clever we can overcome all of these
09:57
seeming biological impediments.
10:00
Well, often we're unaware
10:03
of the fact that we're living
10:05
in environments in which our skin
10:07
is inherently poorly adapted.
10:09
Some of us with lightly pigmented skin
10:12
live in high-UV areas.
10:14
Some of us with darkly pigmented skin
10:16
live in low-UV areas.
10:18
These have tremendous consequences for our health.
10:21
We have to, if we're lightly pigmented,
10:25
be careful about the problems of skin cancer,
10:28
and destruction of folate in our bodies,
10:32
by lots of sun.
10:35
Epidemiologists and doctors
10:37
have been very good about telling us
10:39
about protecting our skin.
10:41
What they haven't been so good about instructing people
10:43
is the problem of darkly pigmented people
10:48
living in high latitude areas,
10:51
or working inside all the time.
10:54
Because the problem there is just as severe,
10:56
but it is more sinister,
10:59
because vitamin D deficiency,
11:01
from a lack of ultraviolet B radiation,
11:03
is a major problem.
11:07
Vitamin D deficiency creeps up on people,
11:09
and causes all sorts of health problems to their bones,
11:11
to their gradual decay of their immune systems,
11:14
or loss of immune function,
11:18
and probably some problems
11:20
with their mood and health,
11:22
their mental health.
11:25
So we have, in skin pigmentation,
11:27
one of these wonderful products of evolution
11:30
that still has consequences for us today.
11:33
And the social consequences,
11:35
as we know, are incredibly profound.
11:37
We live in a world where we
11:40
have lightly and darkly pigmented people
11:42
living next to one another,
11:46
but often brought into proximity initially
11:48
as a result of very invidious social interactions.
11:51
So how can we overcome this?
11:55
How can we begin to understand it?
11:58
Evolution helps us.
12:00
200 years after Darwin's birthday,
12:04
we have the first moderately pigmented President of the United States.
12:08
(Applause)
12:13
How wonderful is that?
12:14
(Applause)
12:16
This man is significant for a whole host of reasons.
12:18
But we need to think about how he compares,
12:22
in terms of his pigmentation, to other people on Earth.
12:25
He, as one of many urban admixed populations,
12:27
is very emblematic
12:31
of a mixed parentage, of a mixed pigmentation.
12:33
And he resembles, very closely,
12:36
people with moderate levels of pigmentation
12:38
who live in southern Africa, or Southeast Asia.
12:41
These people have a tremendous potential
12:45
to tan, to develop more pigment in their skin,
12:47
as a result of exposure to sun.
12:50
They also run the risk of vitamin D deficiency,
12:52
if they have desk jobs, like that guy.
12:56
So lets all wish for his great health,
13:00
and his awareness of his own skin pigmentation.
13:04
Now what is wonderful
13:09
about the evolution of human skin pigmentation,
13:12
and the phenomenon of pigmentation,
13:16
is that it is the demonstration,
13:18
the evidence, of evolution
13:21
by natural selection,
13:24
right on your body.
13:26
When people ask you, "What is the evidence for evolution?"
13:30
You don't have to think about some exotic examples, or fossils.
13:33
You just have to look at your skin.
13:37
Darwin, I think, would have appreciated this,
13:40
even though he eschewed the importance
13:44
of climate on the evolution of pigmentation during his own life.
13:47
I think, were he able to look
13:51
at the evidence we have today, he would understand it.
13:54
He would appreciate it.
13:57
And most of all, he would teach it.
13:59
You, you can teach it.
14:03
You can touch it.
14:06
You can understand it.
14:08
Take it out of this room.
14:10
Take your skin color,
14:13
and celebrate it.
14:15
Spread the word.
14:17
You have the evolution
14:19
of the history of our species,
14:21
part of it, written in your skin.
14:25
Understand it. Appreciate it. Celebrate it.
14:27
Go out. Isn't it beautiful? Isn't it wonderful?
14:30
You are the products of evolution.
14:34
Thank you.
14:37
(Applause)
14:39

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About the speaker:

Nina Jablonski - Anthropologist
Nina Jablonski is author of Skin: A Natural History, a close look at human skin’s many remarkable traits: its colors, its sweatiness, the fact that we decorate it.

Why you should listen

"Much of what we consider our humanity is imbued in our skin," Nina Jablonski tells us. This insight came to her in 1981, as she observed a jittery anatomy class warm to a cadaver only after cutting through its skin. As it turns out, marvels abound of this sweaty, hardwearing, social -- and underappreciated -- organ. Many are collected in her book, Skin: A Natural History, a look at what makes our skin unique and, perhaps, more important than we realize.

A fascination with the multicolored, multi-talented human hide fits Jablonski, a truly eclectic scientist. She's also a paleontologist and primatologist, studying the form, behavior and diet of mammals in light of climate change and evolution. She teaches at Penn State and recently found the world's oldest chimpanzee fossil.

More profile about the speaker
Nina Jablonski | Speaker | TED.com