Breaking the illusion of skin color Nina Jablonski

interestingly Charles Darwin was born a

very lightly pigmented man in a

moderately - darkly pigmented world over

the course of his life

Darwin had great privilege he lived in a

fairly wealthy home he was raised by

very supportive and interested parents

and when he was in his 20s he embarked

upon a remarkable voyage on the ship the

Beagle and during the course of that

voyage he saw remarkable things

tremendous diversity of plants and

animals and humans and the observations

that he made on that epic journey were

to be eventually distilled into his

wonderful book On the Origin of Species

published 150 years ago

now what is so interesting and to some

extent what’s a bit infamous about the

Origin of Species if there’s only one

line in it about human evolution light

will be thrown on the origin of man and

his history it wasn’t until much longer

much later that Darwin actually spoke

and wrote about humans now in his years

of travelling on the Beagle and from

listening to the accounts of explorers

and naturalist he knew that skin color

was one of the most important ways in

which people varied and he was somewhat

interested in the pattern of skin colour

he knew that darkly pigmented peoples

were found close to the equator lightly

pigmented peoples like himself were

found closer to the poles so what did he

make of all this well he didn’t write

anything about it in the Origin of

Species but much later in 1871 he did

have something to say about it it was

quite curious he said of all the

differences between the races of men the

color of the skin is the most

conspicuous and one of the best marked

and he went on to say

these differences do not coincide with

corresponding differences in climate so

he had traveled all around he had seen

people of different colors living in

different places and yet he rejected the

idea that human skin pigmentation was

related to the climate

if only Darwin lived today

if only Darwin had NASA now one of the

wonderful things that NASA does is it

puts up a variety of satellites that

detect all sorts of interesting things

about our environment and for many

decades now there have been a series of

Tom’s satellites that have collected

data about radiation at the Earth’s

surface the Tom’s seven satellite data

shown here show the annual average

ultraviolet radiation at the Earth’s

surface now the really hot pink and red

areas are those parts of the world that

received the highest amounts of UV

during the year the incrementally cooler

colors blues greens yellows and finally

Gray’s indicate areas of much lower

ultraviolet radiation what’s significant

to the story of human skin pigmentation

is just how much of the northern

hemisphere is in these cool grey zones

this has tremendous implications for our

understanding of the evolution of human

skin pigmentation and what Darwin could

not appreciate or didn’t perhaps want to

appreciate at the time is that there was

a fundamental relationship between the

intensity of ultraviolet radiation and

skin pigmentation and that skin

pigmentation itself was a product of

evolution and so when we look at the map

of skin color and predicted skin color

as we know it today what we see is a

beautiful gradient from the darkest skin

pigmentations toward the equator and the

lightest ones toward the poles now

what’s very very important here is that

the earliest humans evolved in high

UV environments in Equatorial Africa the

earliest members of our lineage the

genus Homo were darkly pigmented and we

all share this incredible heritage of

having originally been darkly pigmented

2 million to one and a half million

years ago now what happened in our

history let’s first look at the

relationship of ultraviolet radiation to

the Earth’s surface in those early days

of our evolution living at the equator

we were bombarded by high levels of

ultraviolet radiation the UVC the most

energetic type was occluded by the

Earth’s atmosphere but UVB and UVA

especially came in unempioyed UVB turns

out to be incredibly important it’s very

destructive but it also catalyzes the

production of vitamin D in the skin

vitamin D being a molecule that we very

much need for our strong bones the

health of our immune system and myriad

other important functions in our bodies

so living at the equator we got lots and

lots of ultraviolet radiation and the

melanin this wonderful complex ancient

polymer compound in our skin served as a

superb natural sunscreen this polymer is

amazing because its present in so many

different organisms melanin in various

forms has probably been on the earth a

billion years and has been recruited

over and over again by evolution as

often happens why change it if it works

so melanin was recruited in our lineage

and specifically in our earliest

ancestors evolving in Africa to be a

natural sunscreen where it protected the

body against the depredations of

ultraviolet radiation the destruction or

damage to DNA and the breakdown of a

very important molecule called folate

which helps to fuel cell production and

reproduction in the body

so it’s wonderful we evolved this very

protective

wonderful covering of melanin but then

we moved and humans dispersed not once

but twice major moves outside of our

equatorial homeland from Africa into

other parts of the old world and most

recently into the new world when humans

dispersed into these latitudes what did

they face well can conditions were

significantly colder but they were also

less intense with respect to the

ultraviolet regime so if we’re somewhere

in the northern hemisphere look at

what’s happening to the ultraviolet

radiation we’re still getting a dose of

UVA but all of the UVB or nearly all of

it is dissipated through the thickness

of the atmosphere in the winter when you

are skiing in the Alps you may

experience ultraviolet radiation but

it’s all UVA and significantly that UVA

has no ability to make vitamin D in your

skin so people inhabiting northern

hemisphere ik environments were bereft

of the potential to make vitamin D in

their skin for most of the year

this had tremendous consequences for the

evolution of human skin pigmentation

because what happened in order to ensure

health and well-being these lineages of

people dispersing into the northern

hemisphere lost their pigmentation there

was natural selection for the evolution

of lightly pigmented skin here we begin

to see the evolution of the beautiful

sepia rainbow that now characterizes all

of humanity lightly pigmented skin

evolved not just once not just twice but

probably three times not just in modern

humans but in one of our distant

unrelated ancestors the Neanderthals a

remarkable remarkable testament to the

power of evolution humans have been on

the move for a law

time and just in the last 5,000 years at

increasing rates over increasing

distances here are just some of the

biggest movements of people voluntary

movements in the last 5000 years look at

some of the major latitudinal

transgressions people from high UV areas

going to low UV and vice versa and not

all these moves were voluntary between

1520 and 1867 twelve million five

hundred people were moved from high UV

to low UV areas in the transatlantic

slave trade

now this had all sorts of invidious

social consequences but it also had

deleterious health consequences to

people so what we’ve been on the move

we’re so clever we can overcome all of

these these seeming biological

impediments will often we’re unaware of

the fact that we’re living in

environments in which our skin is

inherently poorly adapted some of us

with lightly pigmented skin live in high

UV areas some of us with darkly

pigmented skin live in low UV areas

these have tremendous consequences for

our health we have to if we’re lightly

pigmented be careful about the problems

of skin cancer and destruction of folate

in our bodies by lots of Sun

epidemiologists and doctors have been

very good about telling us about

protecting our skin what they haven’t

been so good about instructing people is

the problem of darkly pigmented people

living in high latitude areas or working

inside all the time because the problem

there is just as severe but it is more

sinister because vitamin D deficiency

from a lack of ultraviolet B radiation

is a major problem

vitamin D deficiency creeps up on people

and causes all sorts of health problems

to their bones to their gradual decay of

their immune systems or loss of immune

function

and probably some problems with their

their mood and health their mental

health so we have in skin pigmentation

one of these wonderful products of

evolution that still has consequences

for us today and the social consequences

as we know are incredibly profound we

live in a world where we where we have

lightly and darkly pigmented people

living next to one another but often

brought into proximity initially as a

result of very invidious social

interactions so how can we overcome this

how can we begin to understand it

evolution helps us 200 years after

Darwin’s birthday we have the first

moderately pigmented President of the

United States how wonderful is that this

man is significant for a whole host of

reasons but we need to think about how

he compares in terms of his pigmentation

to other people on earth he as one of

many urban admixed populations is very

emblematic of a mixed parentage mixed

pigmentation and he resembles very

closely people with moderate levels of

pigmentation who live in southern Africa

or Southeast Asia

these people have a tremendous potential

to tan to develop more pigment in their

skin as a result of exposure to Sun they

also run the risk of vitamin D

deficiency if they have desk jobs like

that guy so let’s all wish for his his

great health and his awareness of his

own skin pigmentation now what is

wonderful about the evolution of human

skin pigmentation and the phenomenon of

pigmentation is that it is the

demonstration the evidence of evolution

by natural selection right on your body

when people ask you what is the evidence

for evolution

you don’t have to think about some

exotic examples or fossils you just have

to look at your skin Darwin I think

would have appreciated this even though

he eschewed the importance of climate on

the evolution of pigmentation during his

own life I think were he able to look at

the evidence we have today he would

understand it he would appreciate it and

most of all he would teach it you you

can teach it you can touch it you can

understand it take it out of this room

take your skin color and celebrate it

spread the word

you have the evolution of the history of

our species part of it written in your

skin understand it appreciate it

celebrate it go out isn’t it beautiful

isn’t it wonderful you are the products

of evolution thank you

you