Skin color is ‘bone-deep’
This is a sculptor's rendering of Australopithecus afarensis, an ancient human relative that lived 3.2 million years ago.
May 4th, 2013
06:00 AM ET

Skin color is ‘bone-deep’

By Kelly Murray, CNN

From the darkest brown to the pastiest white and every shade in between, humans display a tremendous variety of skin colors. Human skin color is directly linked to our survival as a species as we lost our fur and developed a need for protection from the sun, and then migrated into cloudier regions of the globe. Over the course of evolution, scientists argue, skin color was influenced, among other factors, by our need for healthy bones.

To begin to explain this, we turn to Nina Jablonski, professor of anthropology at Pennsylvania State University. She is a well-recognized researcher in primate evolution, and specifically the evolution of human skin, and she was the subject of a Science Seat on CNN Light Years.

The story of human skin color begins with our furry ancestors about 6 to 7 million years ago in Africa, the last time that humans and chimpanzees shared an ancestor. Jablonski says that these ancestors, called Australopithecus, still had ape-like body proportions: fairly long arms and relatively short legs.

“When we look at their skeletons in detail, it’s pretty clear that they were not active runners,” she said. “They could walk on two legs but they weren’t running or striding purposefully across the savannah most of the time, they were sort of living lives that are much like those of chimpanzees: fairly close to the edge of the forest, sometimes going into trees for protection, and then walking for short distances in the open to forage.”

By about 1.2 million years ago, humans ancestors had lost their fur and were able to sweat more efficiently to avoid overheating. The fossil record shows this in the species Homo ergaster, for example. During this time, individuals began to walk across the hot savannah, so there was a need for more internal body heat regulation.

Without fur, however, our skin was exposed to the strong equatorial sun. The skin pigment melanin, which is responsible for most of the color of our skin, is a terrific sunscreen. Darkly pigmented skin became a substitute for fur.

But as our ancestors migrated away from the Earth’s equator, which has lots of UV exposure, it became less and less beneficial for those populations to have so much pigmentation as protection from the sun. Why? For answers, we must look at vitamin D.

“Vitamin D is produced at high levels in the skin when it is exposed to ultraviolet light from the sun,” says Dr. Michael Holick, a professor of medicine, physiology and biophysics at Boston University Medical Center. He is a leader in vitamin D nutrition, and among countless other works, published the book “The Vitamin D Solution.”
According to Holick, back in the 1930s to 1950s, it was thought that the main reason for skin pigmentation was to prevent having too much vitamin D being produced in the skin. Too much vitamin D leads to vitamin D intoxication, which can result in death. However, in the early 1980s, Holick and his colleagues published a paper that disproved that theory.

“It turns out that Mother Nature was quite clever, in that any excessive exposure to sunlight destroys any excess vitamin D produced in the skin,” Holick explained.

Vitamin D is produced in skin that’s exposed to the sun, and it’s involved in helping the intestines absorb calcium, which is a critical nutrient in our bones. However, heavily pigmented skin reduces a person’s ability to produce vitamin D in the skin “probably by 90-95%,” according to Holick, meaning they were more likely to be deficient in the vitamin.

As our ancestors migrated to areas away from the equator, with lower UV radiation, pigmentation became a problem. For example, Holick explained, a person from Africa who is very darkly pigmented has a sun protection factor of around 30. That person would have to be out in the sun at least 10 to 15 times longer to produce the same amount of vitamin D as a lightly-pigmented person from Europe.

Vitamin D is critical for healthy bones, which have always been essential to human survival. Not only are healthy bones important to movement and holding our bodies upright, but they are essential for reproduction. A pregnant mother who is vitamin D deficient can have a baby born with infantile rickets syndrome, a disease that leads to severe bone abnormalities. If the mother remains vitamin D deficient, she is also calcium-deficient. If breast milk is the main food source for the infant, the infant will not receive enough calcium to build healthy bones.

The female infant "will have a flat, deformed pelvis with a small pelvic outlet, making child delivery impossible,” Holick said.

While rickets may not have affected male reproductive abilities as much, it would have given them weaker, more brittle bones, increasing their risk of fracture, and therefore affecting their ability to survive.

Vitamin D deficiency is associated with a host of other health problems, such as preeclampsia, asthma, upper respiratory infections in children, and even multiple sclerosis, Holick said. This is because of the vitamin’s role in immune function, as it is thought to decrease risk of developing autoimmune diseases.

On the other hand, scientists know that too much sun can deplete a person’s reserve of folate, a B-vitamin that is necessary for cell division and repair and known to reduce risk of fetal birth defects. A big source of folate comes from leafy green vegetables, but Holick argues that our hunter-gatherer ancestors would have eaten plenty of those. Today, many people do not eat enough of them.

So how much sun do modern humans actually need? Dr. Holick says that it’s not possible to give an absolute recommendation because of the time of day, latitude and skin pigmentation, which all influence vitamin D production.

“For example, a lightly pigmented person in Boston in June at noontime, 10 to 15 minutes of sun exposure between the hours of 10 AM and 3 PM on arms, legs and abdomen and back when appropriate 2 to 3 times a week is usually sufficient,” Holick said.

Now that most humans in modern society spend most of their days indoors, away from sunlight, you might assume that humans will eventually become homogeneous in terms of skin color and may lose darker pigmentation.

But Jablonski offers a different explanation for why human skin color will become more homogenous:

“Because of human migrations, especially in the world’s largest cities, skin color will become somewhat more homogeneous because of increased admixture of people, while depopulated rural areas will tend to remain much as they are.”

She emphasizes that that increased color homogeneity will result as a product of the intermingling of populations, not natural selection.

“There is no significant evolution acting on people who are either ‘too light’ or ‘too dark’ for their solar conditions because we have layers of protection in the form of complex culture, like buildings, clothing and diet,” she asserted.

Any city-dwelling person, regardless of skin color, can become vitamin D deficient if he or she doesn’t receive enough sun exposure. As Jablonski explained, just as lighter-skinned people are more likely to suffer from sunburn and therefore skin cancer, darker-skinned people experience more vitamin D deficiency because short periods of outdoor exposure aren’t sufficient to allow them to produce enough vitamin D in the skin.

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Filed under: Human ancestors • On Earth
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    July 31, 2013 at 11:31 pm |
  2. Pedrodevaca

    Most people here, whether creationist or evolutionist (and they are not mutually exclusive despite all the arguing), are not taking into account that even though evolutionary theory is well supported, it does not explain all of the biological variation we observe on Earth, nor does it claim to do so. There remains room for other theories. That does not mean evolutionary theory is a pile of junk. That means that the ability of evolutionary theory to explain all life on Earth is limited.

    Secondly, Darwin has been proven wrong on numerous details, for instance the discovery of and development of the field of genetics, but that does not mean that evolutionary theory is a pile of junk. Instead, quite the contrary, evolutionary theory has been tested, corrected, subject to new discoveries, refined, etc.

    Lastly, evolutionary theory has nothing to do with God. It does not disprove the existence of God nor disprove creation theory. In fact, it doesn't address the presence or absence of God what so ever. Evolution and Creation serve, in part, as explanations for the origins of humanity but with different objectives and different temporal contexts and therefore the two explanations are not mutually exclusive.

    Any insistence by a evolutionist that evolutionary theory disproves God is subscribing to dogmatic extensions of the theory that are not part of the theory at all. Similarly, fundamentalist creationists who insist evolution is wrong because of a literal interpretation of Genesis stories within the Old Testament or a literal interpretation of the Hebrew Calendar (the original source for the 6,000-10,000 year old Earth commonly referenced by contemporary Protestant Christians) are subscribing to dogmatic interpretations of the sources. However, these literal interpretations are not called for by either of the respective fields. What I mean is that nowhere in either field is it necessary to subscribe to these literal interpretations to accept generally the explanation of creation provided by the field.

    It is the narrow-minded dogmatic approaches to either explanation that fosters this division between creationists and evolutionists, not the explanations themselves. Christians and P.h.d.'s alike fall victim to this narrow-minded approach. It is not at all surprising considering that the act of insisting that one's own way of thinking, behaving, and believing is the most righteous, most correct way, is a common human vice that has driven the course of history for thousands of years.

    July 12, 2013 at 2:13 pm |
  3. Bernie Smaldone

    During the past decades doctors have become increasingly aware of the increase in skin cancer in the United States and that all people need to protect themselves from ultraviolet radiation (UV). The harm caused by UV includes premature aging (such as wrinkling and age spots), skin cancer, and permanent, sometimes blinding, damage to eyes.`......

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    July 6, 2013 at 1:32 am |
  4. guptil

    There is some great advice here and all of the poses are easily achievable without looking forced or contrived. I particularly like pose 7 which can make a very dramatic bridal portrait shot in the right location and light. I’ll check out the app for more ideas.

    July 3, 2013 at 3:03 pm |
  5. Wong

    Well, before I head out. I would just like to add this in. I appreciated your post quite a lot. I just had one question. Are you able enough to build upon what you've said here?

    May 9, 2013 at 7:59 pm |
  6. Reticuli

    Another reason why the tanning tax was not science-based.

    May 7, 2013 at 9:26 pm |
  7. Ric B

    Articles like this lead t responses that really show the lack of science education in this country.

    May 7, 2013 at 11:06 am |
    • Reticuli

      Our president isn't the most science-educated, himself. I voted for the guy and am embarrassed by the tanning tax and the d-bag population control advocate he appointed as WH science advisor. Pretty sad.

      May 7, 2013 at 9:28 pm |
  8. MassiveMarbles

    The best way to keep us apart is to spread word of our differences. You Get a Gold Star

    May 6, 2013 at 4:29 pm |
  9. StarGazer

    No mention of sunscreen? It's recommended after your required dose of sun.

    May 6, 2013 at 7:13 am |
  10. StarGazer

    I'm surprised they didn't mention the fact that some skin tones need sunscreen after you get your required amount of sun.

    May 6, 2013 at 7:06 am |
  11. jokerman

    I always heard that ugly went clean to the bone.

    May 5, 2013 at 9:58 pm |
  12. No Man

    Lamarkian Evolution lives! Perhaps this "scientist" should go back and review Darwinian V Lamarkian evolutionary theory!
    Evolutionary advantages don't just develop over time – those advatages, whatever they might be, are present and selected for and or against in varying environments.

    May 5, 2013 at 9:46 pm |
  13. Possum

    Evolution is a fact. We see evolution all the time – the development of new strains of influenza, introduction of HIV into humans and resistance to antimicrobials and pesticides are examples of evolution. The variety in domestic animals – pygmy horses vs Clydesdales,and shih tzus vs mastiffs are a form of evolution except the selective pressure is man as opposed to nature. This may be a theory but it is supported by a lot fact.

    May 5, 2013 at 9:06 pm |
    • John P. Tarver

      The slow change over time is something widely known long before Darwin. However, the notional hypothesis that species are an outcome of evolution is false. The photo of an ape, when speculating as to evolution of pigment, is pure racism.

      May 5, 2013 at 9:32 pm |
      • Ric B

        The article is about Vitamin D!Go look at your milk carton – do you even understand WHY the FDA makes the milk manufacturers infuse Vitamin D in your milk?

        May 5, 2013 at 9:39 pm |
      • John P. Tarver

        As a Pixy I have very little pigment and the sun provides the D I need. Evolution is a fact well known for several millenia before Darwin was born. Darwin's conclusion that species are an outcome of evolution is false. The image of an ape at the top of this article is racist, not science.

        May 5, 2013 at 9:47 pm |
  14. SillyRabbit

    The word "Theory" in science, has different meaning than the word "Theory" in any other part of life. I encourage you to read this article on one controversial scientific theory (http://en.wikipedia.org/wiki/Evolution_as_fact_and_theory) One could easily apply the same explanation made in this article to any other non-controversial scientific "theory" if you would prefer, such as Circuit Theory, Gravitational Theory, or any of the other thousands of "Theories" we have in Science.

    Regarding the statement of using Science to "discredit" religion.... This seems to imply that the two are somehow on equal ground.... Which is not the case. Religion or Faith, is something you either believe or not. It is something that doesn't require evidence nor does it require facts. It's something that can be complete nonsense, with no facts to support it or there can even be facts that disprove it (fact: the earth is not 6000 years old), but you can still believe it. Much like my belief in Santa. I believe in Santa, because it makes the pagan celebration of Sol and Victus (known as a Christmas today) more enjoyable to me.

    Science, however, is not something you can believe in or not. It is something you either acknowledge or you don't. It is something backed by research, evidence, and continuously evolving knowledge. Science doesn't care about your religion and it also doesn't care if you want to take that which we don't know or understand about the Universe and say "you don't understand it, it must be god". It's fine for you to think that, but if you are content enough with that answer, that you stop researching, you stop trying to understand how it works or "how god made it work" if that is your belief, then you are useless in the Scientific field.

    Point being: Science is not, nor has it ever been some evil force that wants to discredit or disprove religion. It simply doesn't care about religion. Religion however, has made many efforts to hinder scientific research and development. And that's a problem.

    May 5, 2013 at 8:49 pm |
    • John P. Tarver

      Evolution as a means tom species was never a theory under the scientific method. A theory under the scientific method must be demonstrable and repeatable, like relativity; where we know gravity is mass bending time.

      May 5, 2013 at 9:36 pm |
  15. Tulipo

    Everyone please read.

    http://www.talkorigins.org/faqs/evolution-fact.html

    May 5, 2013 at 6:27 pm |
    • John P. Tarver

      Talk origins believes horses are an example of natural selection, not very much science there.

      May 5, 2013 at 7:55 pm |
  16. JL

    Whoops, didn't know I stumbled into one of the fairy tale sections of CNN. Caution, they have several.

    May 5, 2013 at 6:18 pm |
  17. Walter Gates

    I see zero conflicts between evolution and creationism. Period. I think it is unreasonable and self-centered to say otherwise. To be perfectly honest, none of us were there to observe thousands of years of evolution just as none of us are God. I see the fossil record that heavily supports (if not proves) evolution as increased evidence that a higher power exists, not less. It seems highly unlikely that a omnipotent supreme being grabbed some clay and made everything ever in a day shy of a week. It seems much more credible that the will to survive, the sheer genetic luck rendered upon some populations, and the improbable right-place-right-time of all existence was guided in some part by a higher power.

    Evolution gives credence to creationism.

    May 5, 2013 at 5:51 pm |
    • John P. Tarver

      The fossil record disproved evolution as a means to species 40 years ago. Species occur rapidly following a mass extinction, the opposite of evolution.

      May 5, 2013 at 7:56 pm |
      • Ric B

        LOL – you are hysterical - this is good comedy for anyone who has had any amount of science education in the last 30 years. How old are you – 80???

        May 5, 2013 at 8:09 pm |
      • John P. Tarver

        Dr. Gould provides 1400 pages of peer reviewed evidence to reconcile the notional hypothesis that evolution is a means to species with the global geological record. His baseless assertion afterwards is that punctuated evolution must be true since Darwin is false.

        May 5, 2013 at 9:41 pm |
      • Ric B

        You are simply put – a liar. You, like all of the science deniers I have ever met make up your own facts because you have no credible ones of your won. If Dr Gould were alive today he would choke you! Stephen Jay Gould (September 10, 1941 – May 20, 2002) was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation. Gould spent most of his career teaching at Harvard University and working at the American Museum of Natural History in New York. In the later years of his life, Gould also taught biology and evolution at New York University near his home in SoHo.
        Gould's most significant contribution to evolutionary biology was the theory of punctuated equilibrium, which he developed with Niles Eldredge in 1972. The theory proposes that most evolution is marked by long periods of evolutionary stability, which is punctuated by rare instances of branching evolution. The theory was contrasted against phyletic gradualism, the popular idea that evolutionary change is marked by a pattern of smooth and continuous change in the fossil record.

        May 5, 2013 at 9:53 pm |
      • John P. Tarver

        Dr. Gould would have strangled me when he was alive over my use of his work at talk.origins, except that I am a 1%er and he would not have therefore had little hope of surviving. Fact is Dr. Gould applied the fossil record from geology, along with the iridium-24 layer, to further biology beyond the ant study. Darwin's notional hypothesis is false, the standard Darwin arrogantly created and called the "scientific method", even though Issac Newton had already created a standard of the same name.

        May 5, 2013 at 10:10 pm |
      • SillyRabbit

        It is so sad that retards like you are out there influencing public policy..... please go search for the edge of the "flat earth" and jump off when you find it

        May 5, 2013 at 8:53 pm |
      • John P. Tarver

        Is silly rabbit your science avatar? The global geological record includes a layer of iridium-24 with new species in one era and old species on the other side; of this physical marker of mass extinction.

        May 5, 2013 at 9:34 pm |
  18. Jayleigh

    It is sad and funny to read comments...I just read someone argue against evolution saying it is a theory....like gravity....and cannot be proved. Gravity is a law, newton proposed he theory. It has been proven. Evolution is no different. You may believe god dropped us out of the sky and we did not evolve from monkeys. That is fine, but do not be ignorant and dispute that evolution exists at all.

    May 5, 2013 at 5:37 pm |
    • John P. Tarver

      Evolution as a means to species was never a theory, however gravity is mass bending time, as we know from the theory of relativity.

      May 5, 2013 at 7:57 pm |
  19. Steve

    The above picture, obama's uncle??

    May 5, 2013 at 5:22 pm |
  20. shawbrooke

    Sounds good, but this is rampant speculation and there is no evidence for any of it. Where is the evidence that our ancestors were covered in fur in the first place? There is much to be learned and I am waiting for it. In the mean time, the media should spare us the speculation, or at least put it in the National Enquirer.

    May 5, 2013 at 5:20 pm |
  21. HurrZ

    Judging by the illustration, the primitive pre-humans were dark skinned.

    Why is that?

    May 5, 2013 at 4:39 pm |
  22. dikoosh

    Looks like an ugly monkey to me.

    Maybe that's your great grandfather but I was created by God.

    May 5, 2013 at 4:21 pm |
    • Joseph Bleaux

      Which god? Zeus, Manitou, Krishna, Yahweh, Zoroaster? There are so many invisible sky fairies I lose track. All the gods that have been worshiped throughout history would fill 10 football stadiums, but of course YOURS is the only one that's real. Grow a brain, dimwit. All religions are nothing but ancient mythology, written thousand of years ago by members of a primitive culture. I'll take modern scientific knowledge over ancient mythology any day.

      May 5, 2013 at 4:47 pm |
      • Walter Gates

        Or there is a degree to merit in all religions. Do not a steadfast majority of world religions promote peace, love, service, and cooperation. It's like telling the same story in a different language or cultural setting. It doesn't mean it's wrong. In fact science can be described as no more than a retelling of these quintessential tales. Humanity is simply given a how to a pre-established why.

        May 5, 2013 at 5:54 pm |
      • Joseph Bleaux

        There is merit in some fairytales too, but they're still fairytales, just like religion.

        May 5, 2013 at 8:31 pm |
  23. Buck Rogers

    Oh boy, here we go again.... Mankind 'evolved' from apes 'n monkeys... Earth is billiards of years old and 'spins' and 'wobbles' on an axis shot from a cosmic cannon..... And this evolutionary junk is labeled as "science"... One thing is certain, mankind's 'evolutionary science idol' and his vain attempts at duping the masses with such nonsense does indeed provide comic relief for those of us who know better.

    http://www.fountainsofthegreatdeep.com/IFS.htm

    May 5, 2013 at 4:11 pm |
    • Joseph Bleaux

      Learn to spell and use proper grammar. Then people might take your ignorant opinion seriously. But... probably not.

      May 5, 2013 at 4:44 pm |
  24. religion

    hey everyone! It's a picture of jesus.

    May 5, 2013 at 3:22 pm |
  25. Sheldon

    All of you holy rollies, geeks, nerds, self proclaimed genious dweebs make my brain hurt, not to mention waste my time.

    May 5, 2013 at 3:02 pm |
  26. Rachael

    Would the lunatic religious people get away from everything science and stop interfering with the sciences please? I've had enough of hearing about how you may attack everyone and everything because some book written in 600BC tells you how to think AND you tell everyone else to think that way. Otherwise this is an excellent article of scientific research. Maybe someday the sciences will learn how to implant brain cells into the religious fanatics so we don't have to hear them rant everytime a scientific article comes out.

    May 5, 2013 at 2:56 pm |
    • Mark

      If you think the bible was written in 600 BC then you really should avoid discussing the subject.

      May 5, 2013 at 4:22 pm |
      • GCode

        Lol

        May 5, 2013 at 5:49 pm |
    • MrChameleon

      You shouldn't talk about things you don't have any truthful knowledge about. Science has been wrong more times then the Weatherman when it comes to the past. Every so called "new discovery" they adopt is to cover up the previous flaw in theory.

      The truth is, Science has a far less chance of discovering the truth then a series of history books that were written over a span of several thousands years.

      The ego's of Scientists can't bare to bring themselves to the reality that there is something of the Universe greater then themselves. What happens to their lives when Science proves God exist? Do they undermine the discovery and wish it away? GL with that, certainly they will try their best. 😉

      May 5, 2013 at 6:17 pm |
  27. John P. Tarver

    This is just more proof that liberalism is an outcome of guilt over racism. DNA has shown that Ape is not an ancestor of Man, neither do Man and Ape share a common ancestor. Species occur rapidly following a mass extinction, the opposite of evolution.

    May 5, 2013 at 2:06 pm |
    • paul

      so you just demonstrated you no NOTHING of biology,chimps and humans share 96%of our DNA that ignorant sir is a FACT...no go away and let the adults talk

      May 5, 2013 at 2:23 pm |
    • John P. Tarver

      Science is what I am discussing, but the atheist religion is what this article is about. Ape did not make blacks and then they evolved into whites, that is racism, not science.

      May 5, 2013 at 2:30 pm |
      • Soda Bob

        Of course not, nobody said apes turned into blacks, who turned into whites. We all share a common ancestor with apes, including our closest DNA "cousin" the chimps.

        May 5, 2013 at 7:37 pm |
      • John P. Tarver

        DNA has proven that Man and Ape do not share a common ancestor, unless you mean that little rat from US Riverside Biology. What you are writing is racism, not science bob.

        May 5, 2013 at 7:43 pm |
      • kabs kubs

        @John P. Tarver,for a science page like this,you're rather too enthusiastically waving your flag of ignorance by calling Atheism a religion.

        May 5, 2013 at 9:51 pm |
      • John P. Tarver

        Atheism finds it's basis in science that has become outdated. The fossil record demonstrates beyond any doubt that species occur rapidly following a mass extinction, the opposite of evolution. Relativity proved that time-space is not real and cancelled the big bang a century ago, but the big bang remains a pillar of the atheist religion.

        May 5, 2013 at 10:14 pm |
      • Ric B

        You are truly an illiterate. Dr Gould – who you falsely accused of disproving evolution -demonstrated that there are periods of rapid evolutionary development in the development of species. This is not in opposition to evolutionary theory that you nut jobs so desperately want – it merely suggests that evolution comes in rapid periods like tens of missions of years – instead of slow periods – like hundreds of missions of years! You really are a nut job troll who has no understanding of science or how it produces results.

        May 5, 2013 at 10:23 pm |
    • SkepticalOne

      Stop discussing science and find a topic that you know something about.

      May 5, 2013 at 2:43 pm |
      • John P. Tarver

        I believer my master of engineering gets me way past yourself in science skeptic troll. Darwin's notional hypothesis that evolution is a means to species was proven false by geology 40 years ago. A theory must be experimentally demonstrable and repeatable, like relativity. Darwin's racism was never a theory under the scientific method.

        May 5, 2013 at 7:54 pm |
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