Session 5.1b - Pre-Reading - Skin Pigmentation Evolution

Question 1

Which part of the world receives the highest UV radiation?

Answer 1

Near the equator, with decreasingly incremental amounts near the poles.

Question 2

Fig. 3:15

What is significant about the Northern Hemisphere?

Answer 2

Much of it is in the cool gray zones (which receives less UV radiation as compared to the equator).

Question 3

What is the relationship between skin pigmentation and evolution?

Answer 3

Human skin pigmentation/colour is the product of evolution, to the zones of UV radiation, by natural selection.

Question 4

What is the relationship between human skin colour and UV radiation?

Answer 4

When we look at a map of skin colour, and predicted skin colour, as we know it today, what we see is a beautiful gradient from the darkest skin pigmentations towards the equator, and the lightest ones toward the poles

Question 5

Where did the earliest human originate?

Answer 5

The earliest humans evolved in high-UV environments, in equatorial Africa.

Question 6

What are the earliest members of our lineage known as?

Answer 6

Genus - homo

Question 7

What colour were the earliest humans?

Answer 7

The earliest members of our lineage, the genus Homo, were darkly pigmented.

Question 8

When were the earliest humans born?

Answer 8

Two million to one and half million years ago

Question 9

What race do we all share common ancestry with?

Answer 9

The earliest members of our lineage, the genus Homo, were darkly pigmented, so we all share this incredible heritage of having originally been darkly pigmented, two million to one and half million years ago

Question 10

What happened to the UV radiation in our history?

Answer 10

Let’s first look at the relationship of ultraviolet radiation to the Earth’s surface. In those early days of our evolution, looking at the equator, we were bombarded by high levels of ultraviolet radiation

Question 11

What are the 3 types of UV radiation emitted by sunlight?

Answer 11

UVA
UVB
UVC

Question 12

Describe some facts about UVA sunlight at the equator.

Answer 12

• It can come into the Earth’s atmosphere, unimpeded

Question 13

Describe some facts about UVB sunlight at the equator.

Answer 13

• It can come into the Earth’s atmosphere, unimpeded
• It’s very destructive
• But it is incredibly important: it catalyses the production of vitamin D in the skin

Question 14

Describe some facts about UVC sunlight.

Answer 14

• The most energetic type (out of UVA, UVB and UVC)

- Occluded by the Earth’s atmosphere

Question 15

What catalyses the production of vitamin D in the skin?

Answer 15

UVB radiation (found in sunlight)

Question 16

What is vitamin D?

Answer 16

A molecule that we very much need for our
- strong bones
- health of our immune system
- myriad other important functions
in our bodies

Question 17

What serves as a natural sunscreen to UV radiation?

Answer 17

Melanin

Question 18

What happens to people who live at the equator?

Answer 18

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.

Thus, we developed more melanin due to natural selection, showing that skin pigmentation was a result of evolution.

Question 19

What is melanin?

Answer 19

A wonderful, complex, ancient polymer compound in our skin – serves as a superb natural sunscreen

Question 20

What is the function of melanin?

Answer 20

To serve as a natural sunscreen.

Question 21

What organisms is melanin found in?

Answer 21

This polymer is amazing because it’s 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.

Question 22

How long has melanin been on the Earth for?

Answer 22

Probably about a billion years.

Question 23

Where did our earliest ancestors evolve?

Answer 23

In Africa

Question 24

What does melanin protect the body against?

Answer 24

The degradations of ultraviolet radiation, the destruction, or damage to DNA, and the breakdown of a very important molecule called folate

(Protection against damage to DNA and breakdown of folate)

Question 25

What is the relationship between folate and sunlight?

Answer 25

UV radiation from sunlight can lead to the breakdown of folate, which is damaging. because our body needs folate.

Question 26

What is the function of folate?

Answer 26

Helps to fuel cell production and reproduction in the body.

Question 27

What is the difference between the Northern Hemisphere and the equator?

Answer 27

Conditions are significantly colder, but they are also less intense with respect to the ultraviolet regime

Question 28

How is skin colour protective?

Answer 28

Darkly pigmented skin is highly protective under intense UVR regimes

Question 29

What is the Old World and New World?

Answer 29

Old World = Africa, Asia and Europe

New World = America and Oceania

(Western hemisphere)

Question 30

Where did humans migrate?

Answer 30

“And humans dispersed – not once, but twice”
- First humans originated in Africa

Then, they moved to other parts of the Old world

THEN, more recently, into the New World

Question 31

What happens to UVA radiation in the Northern Hemisphere?

Answer 31

We still get a dose of it

Question 32

What happens to UVB radiation in the Northern Hemisphere?

Answer 32

All of the UVB, or nearly all of it, is dissipated through the thickness of the atmosphere

Question 33

Do you experience more or less UV radiation skiing in the Alps or at the equator? Explain your answer.

Answer 33

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

At the equator, you experience more UVB radiation, which is able to make vitamin D BUT can also damage DNA/breakdown folate.

So you don’t experience more or less, just different types of UV radiation.

Question 34

What is significant about UVA radiation?

Answer 34

It is more common in the Northern hemispheres but you cannot make vitamin D from it.

Question 35

Describe some facts about UVA.

Answer 35

• It can come into the Earth’s atmosphere, unimpeded
• In the Northern Hemisphere, it is mostly UVA that is found
• This is important because UVA CANNOT make vitamin D

Question 36

Describe some facts about UVB.

Answer 36

• It can come into the Earth’s atmosphere, unimpeded at the equator
• It’s very destructive
• But it is incredibly important: it catalyses the production of vitamin D in the skin
• However, in the Northern Hemisphere, all (or nearly all) of the UVB is dissipated through the thickness of the atmosphere (meaning mainly UVA radiation occurs in the Northern Hemisphere).

Question 37

What is the relationship between vitamin D and lighter-skinned people?

Answer 37

So people inhabiting northern hemispheric environments were bereft of the potential to make vitamin D in their skin for most of the year.

Question 38

Explain how vitamin D is related to evolution.

Answer 38

• Vitamin D production occurs from UVB radiation of sunlight into the skin
• UVB radiation is most pronounced at the atmosphere
• Therefore, populations in the Northern Hemisphere were bereft of the potential to make vitamin D for most of the year
• This had tremendous consequences for the evolution of human skin pigmentation: people dispersing into the Northern Hemisphere lost their pigmentation to maximise vitamin D production
• There was natural selection for the evolution of lightly pigmented skin.

Question 39

Why did people in the Northern Hemispheres lose their pigmentation?

Answer 39

• Less UVB rays in the Northern Hemisphere which allows vitamin D production (compared to the equator)
• Melanin, which also gives people their skin colour, protects the body from excess UVB radiation
• So less melanin was produced to allow more UVB radiation through in the Northern Hemispheres (where there was less UVB penetration from the atmosphere)
• This means vitamin D production can be maximised.

Question 40

What evolution occurred relating to UVB production?

Answer 40

Depigmented skin evolved to maximise vitamin D production in the skin

Question 41

When did evolution of skin colour occur?

Answer 41

• As humans dispersed out of the tropics, lightly pigmented skin evolved multiples times. … at least twice in Homo sapiens and…

Question 42

When did evolution of skin colour occur?

Answer 42

• As humans dispersed out of the tropics, lightly pigmented skin evolved multiples times. … at least twice in Homo sapiens and… once in Neanderthals

Question 43

What are Neanderthals?

Answer 43

Neanderthals are an extinct species or subspecies of archaic humans in the genus Homo, who lived within Eurasia from circa 400,000 until 40,000 years ago.

Question 44

Make SAQ question about Darwin being white - link into ASBHDS

Answer 44

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