Rough Transcript of Skin Deep Video

Transcription

1 Rough Transcript of Skin Deep Video Professor Joblonski head of the Department of Anthroopology Pennsylvania State University. She's one of the world's leading experts on the issue evolution of of human skin color. Human skin comes in a great variety of colors, but we don't have true black or white or bright red or yellow skin. Rather we have subtle gradations from very dark brown black to almost ivory white. None of these are really stark colors are very subtle and we see an almost infinite gradation from one color to another. Our research work on skin color was really aimed illuminating why the gradient of skin color that we see in modern humans exists. The main pigment in human skin is called melanin and people have it to greater or lesser extents. Melanin is an extraordinary biomolecule. Melanin is produced in the lower layers of the skin by cells known melanocytes. There are two types of melanin eumelanin, which is brown or black and pheomelanin which is red or yellow. The relative amount of these two types of melanin determines the shade of skin color. But as well as providing color melanin provides protection. It6 is well known that moderate dar.. exposure to sunlight can produce a darkening of the skin giving us a suntan.... And But overexposure can produce a nasty case of sunburn or even worse, skin cance. In an effort to protect us from the damaging effects of ultraviolet radiation the skin produces more melanin. Melanin is superior natural sunscreen in that it absorbs UV radiation and it neutralizes chemicals that are formed by UV radiation. So its this remarkable product of evolution. The evolution of human skin color is inextricably tied to the story of human migration. Scientists believe all modern humans are descended from a single group of Homo sapiens who migrated out ofafricaaround 120,000 years ago. Gradually the human population grew as it spread throughout Europe and across Asia to as far away asaustralia. During the epic migration, the incredible sepia rainbow of human skin color slowly evolved. But more recently history saw the launch of an equally epic period of aggressive mass migration across the planet. This was the age of European exploration and colonization. In most places they went, the light skinned Europeans encountered darker skinned indiginouse people for the first time. In Africa, Asia, the Americans, the Pacific andaustralia. The consequences were often disastrous. For many years research into the evolution of skin color was frozen in time because it was considered a socially unpopular subject in which to search. But I felt that when I started doing this research we were mature enough as a society to begin to address this question again to be able to understand the science. The first clue in her journey of scientific discovery came when Jablonski read the epic treatise... Races and People of the World by a 20th-century Italian geographer. It was the first attempt at a serious scientific study of the global distribution of human skin color. It took years as he traveled from population to population, country to country. His maps made from his data showed a gradual transition of skin colors. Jablonski was more interested in why this distribution had evolved. I am certain he had an idea about sunlight being strongly involved in the evolution of skin color. It was quite clear that darkly pigmented people were found in areas with a lot of sun.

2 Jablonski set out to investigate whether there was indeed a direct link between sunlight and global distribution of human skin color. She sought the help of one of her closest collaborators geographer and husband George Chaplin. Chaplain had access to a massive database from NASA satellites showing ultraviolet levels across the planet. Chalpain constructed the most complete record ever compiled of ultraviolet radiation across the globe. We could see that ultraviolet radiation was related to latitude but it was also related to the amount of humidity in the air, the mountains so forth. So ultraviolet radiation is not simply a latitude effect. It is much more complex. They compared the distribution of UV light with the skin color of indigenous people. They found a 90% match between UV radiation and skin color distribution. UV light was an important driver in the evolution of human skin color. This very strong correlation clearly calls for a good evolutionary explanation. So Jablonski is going back to where human evolution began,east Africa, one of the hottest and driest places on earth. This (Eastern Rift Valley) is the cradle of human kind where most of the important phases of human evolution are marked. Over the years research in the rift valley has unearthed large numbers of early human fossils. Some date back millions of years to our most distant ancestor. Humans have been evolving in the Rift Valley for 5 million years. This was a period was one of great environmental change. Scientists have discovered that eastafricawas not always high and dry. Millions of years ago when early Hominids walked the Rift Valley the climate was much wetter and the environment much greener that today. Scientists believe that our early ancestors were covered in hair and like the modern chimpanzee they had light colored skin. But gradually things began to change in the great Rift Valley. In 1984 a discovery was made inkenyathat sent shockwaves around the world. It was the well preserved skeleton of a 12-year-old boy. Research revealed when this boy lived here the forests of eastafricahad become a vhot and dry savannah with animals grazing in open grasslands. Humans in order to survive in this new environment were forced to adapt. Humans about a million and a half years ago looked quite modern in their body proportions and from what we can tell, they were also modern in many of their activities. They were striding walkers and runners and they would have built up a lot of body heat. Those people would have needed to lose excess body through radiant heat loss and from sweating and it's at that point we reconstruct that we would've lost most of our body hair leaving our skin vulnerable to UV radiation. In fact, it was at this time we began to develop permanent dark pigmentation to protect us from ultraviolet radiation. One of the most widespread explanations about why we evolved dark skin was that high levels of melanin protected our early ancestors from skin cancer. But Jablonski would discover the real reason on the other side of the world in a country where skin cancer killed thousands of people every year. Australiahas the highest rate of skin cancer in the world. Over fifty percent of the population will develop some form of skin cancer in their lifetime and conservatively an estimated one thousand seven hundred sufferers die every year. Professor Rick Sturm of the University of Queensland is examining a sample of normal human skin which looks very different than

3 skin affected by the most dangerous form of skin cancer, melanoma. Excessive exposure to ultraviolet radiation is the main cause of skin cancer. For many young people on beach today the damage they do is. a biological time bomb. It is a consequence of living in the southern hemisphere where there are higher rates of UV radiation and also a consequence of genetics because of a large portion of population from northern Europe,IrelandandScotland. The light-skinned population ofaustraliais most susceptible to skin cancer. Unlike indigenous people whose dark skin is perfectly adapted to this ultrahigh UV environment. Aboriginal people have tens times less skin cancer than fair-skinned Australians. The theory that dark skin evolved as a protection against skin cancer seemed persuasive. Jablonski was not convinced. This really didn't make much sense because skin cancer affects people after their reproductive age. So the idea that evolution has to work on something that affects reproductive success kept praying on my mind. Jablonski reasoned that because skin cancer usually develops after our childbearing years it's unlikely that the disease had anything to do with the evolution of skin color. We kept searching to see if there were any new data that might shed light on this and we discovered that different wavelengths of ultraviolet radiation had dramatically different effects on human physiology. Ultraviolet radiation is an invisible component of sunlight and is found beyond the violet end of the visible spectrum. There are a number of different types of UV defined by their different wavelength. The two wavelengths which have the greatest effect on human skin are UVA and UVB. All these UV radiations penetrate down into the skin. UVB can penetrate very little. UVA can penetrate somewhat more. UVA is absorbed by less molecules but there is more of it, of the order of ten to one hundred times more UVA than UV-B. UV-A can penetrate deeper. In fact the longer wavelength of the UV-A radiation enables it to penetrate through the protective of the skin all the way down to the blood stream. The strong correlation between ultraviolet A radiation and skin pigmentation clearly indicated to us that there was something in the blood supply that was being protected by melanin. What is in the blood that effects reproductive success? The answer came with the announcement of groundbreaking new findings into the causes of some types of birth defects. In 1991 I was sitting in a lecture inperth,western Australiawhere I was working and I listened to this fascinating lecture about folate deficiencies and birth defects. That lecture was by renowned Australian epidemiologist Professor Fiona Stanley. We had the most exciting time researching folate in the prevention of spina bifida. Spina bifida and related defects are very severe and the majority children die this with this defect and the others have major paralyses below the lesion which is a spinal cord lesion. How a fetus can be affected by sunlight while still in the uterus can best be understood by looking at the almost unbelievable complexity of the chemical processes involved. The foundations of a nervous system are created in the first weeks of the new embryos life. If at that time certain chemicals are missing or in short supply the consequences can be devastating birth defects. Stanley s research showed a major association between folate deficiency and spinal cord birth defects. Folate is a water-soluble vitamin found in leafy green vegetables and whole grains. It is needed for a large number of the body s biochemical reactions but is especially critical in the production of DNA. Exposure to prolonged or intense UV radiation can destroy folate circulating in the blood. During reproductive years women are particularly vulnerable. Folate is important for developing embryos but it is also important for all sorts of other cellular processes. It is important to men to make healthy sperm. Folate is something that needs to be protected in terms of evolutionary success. For this reason Folate is a mandatory I bread in countries that have high levels of ultraviolet radiation and large populations of fair skinned people. So when I put two and two together that was the evolutionary key I was seeking. It was a small, eureka moment for me. I was sitting in the seminar very squirmy excitement. I was

4 so excited and immediately afterward, I went to talk to Professor Stanley about this idea. She probably thought I was a bit crazy because I was so excited. The development of dark protective skin can be seen as one of the most important milestones in the evolution of the human species. However a fundamental question remained unanswered. What was the evolutionary imperative that saw humans living in low UV environments develop light colored skin. For the answer Jablonksi had to look deep below the surface of the skin to the fundamental building blocks that makes up our genetic inheritance The development of dark skin in human beings living in areas of high UV radiation was an elegant solution to a complex biological problem that saw them perfectly adapted to their environment It required the precise combination of more than one hundred genes providing the genetic codes essential for survival. But surprisingly, hundreds of thousands of years of evolution can be swept away a single mutation. Sisters grace and Martha Zimmerman have inherited a rare genetic disorder. Both suffer from albinism, an absence pigmentation in their skin and in the irises of their eyes. Albinism if caused by a major DNA mutation leaving sufferers with an almost total lack of melanin. For every baby born to parents carrying the mutation there is twenty five percent chance of having a child with albinism. Africans with albinism face discrimination for a trait virtually than among Europeans would go virtually unnoticed. Martha and Grace s fair skin provides little protection from the high UV levels of their equatorial home inkenya. Here dark skin has been essential for survival for over a million years. But Jablonski has found that sunlight holds the secret why humans as they moved away from the equator lost their skin color. The loss of pigmentation in people inhabiting higher latitudes and lower UV level 's lead to increased reproductive success. Lighter skin allows more ultraviolet radiation to penetrate the skin but it wasn't harmful. Quite the opposite it was helpful. The reason why is linked to an important beneficial effect that sunlight has on human health. This crucial link was first revealed during the Industrial Revolution in the late eighteenth century when urban populations in Europe andamericabegan to swell and major health issues started to develop. In big manufacturing cities likenew York,LondonandParis, children begin to develop terrible bone deformities that soon became an epidemic of a disease called Ricketts. It was estimated by the turn of the nineteenth century that upwards of eighty to ninety percent of children living inlondonandglasgowand other urban centers had Ricketts. Scientists soon realized that Ricketts was somehow related to insufficient UV exposure found in sunlight. We realized that ultraviolet radiation was mostly destructive force also had one very constructive and important aspect for humans. UV light is needed to produce vitamin D in the skin. Vitamin D helps the body absorb calcium, strengthening bones and boosting the immune system. The most important source of vitamin E is the shorter wave length UVB radiation in sunlight. The way you make vitamin D in your skin is that there is a form of cholesterol in your skin that absorbs ultraviolet B portion of sunlight and it converts the vitamin D. It turns out that

5 if you are the severely vitamin D deficient for about the first two years of your life, you're at very high risk of having gross retardation and the skeletal abnormalities like Ricketts. At the turn of the last century scientist from all walks of life became involved in trying to understand the cause and trying to find a cure.. And what they concluded was that if you took cod liver oil you could help prevent Ricketts. Cod liver oil is a rich source of Vitamin D. Soon reluctant children throughout the world are being forced fed the fishy oil and by the 1920 s Ricketts was all but cured. Today however Vitamin D deficiency is still one of the most common medical conditions in the world, and dark skinned people living far from the equator are at much higher risk. We did a study ofbostonthat showed that eighty four percent of African-American men and women were Vitamin D deficient at the end of the summer. There are now hundreds of thousands of cases in theunited Statesalone where vitamin D levels need to be boosted through special diet or the use of Vitamin supplements. Our dark ancestors could not have survived in a northern European or North American climate because their skin is so effective as a sunscreen. It would've prevented them from making any sufficient vitamin D. As a result they would have growth retardation, they would have had a difficult time child-birthing, thing they would've had muscle weakness increased risk of infectious diseases. All of those in combination would have caused the demise of dark skinned people as they moved North and South of the equator which is I believe the driver in evolution for de-pigmentation. InCanada sarctic Circle, a unique set of circumstances has led to an interesting exception to the skin color rule. Inuits, the indigenous people of the region don't have the light-colored skin normally associated with low UV environments. For Eskimos and Inuit people when they were killing seals or Polar bear that they would be eating some of the blubber or a slice of the polar bear liver. It turns out that those are excellent sources of vitamin D, so that they learned early on that they needed vitamin D through their dietary sources. This traditional diet was the richest natural source of vitamin D next to sunlight. With such an effective substitute there was little selective pressure here for the Inuit to evolve light colored skin. Today, however Inuit food sources have changed. There is mounting evidence that Inuits that have now taken Western lifestyle is that there are very high risk of vitamin D deficiency and therefore at very high risk of having Ricketts in their children, aching bone pain as adults. So westernized diet certainly is not accommodated their need for vitamin D. So we now know that light colored skin evolved to allow UV-B to penetrate to make Vitamin D and dark colored skin evolved in order to prevent the damaging effects of UV-A (destruction folate). This happened in different populations in response to different UV levels. But incredibly, our skin color can also vary in response to different biological needs over our lifetime. In this village we can see the natural range of variation that you would find in any human population. In this group and the women that are slightly lighter than men in general and

6 you can also see a little baby is much lighter than its mother. This is natural that an infant does not develop much pigmentation until it becomes really a toddler and we really don't develop our full pigmentation until were nearly only reproductively competent adults in our late teen years. The reason why the child has lighter skin than his parents is because he needs more ultraviolet radiation to stimulate the production of vitamin D, so vital for his young growing body. On the other hand his mother and father needed darker skin to protect folate in their bloodstream, which is so important to the production of healthy sperm and to embryonic development. Skin pigmentation is an essential regulator of reproductive success and levels of pigmentation have evolved because they determine levels of vitamins that are essential to reproductive success. All pieces didn't seem to be falling into place. One more important piece of the puzzle was found in 2005 when a cancer researcher was studying the black and white stripes of zebrafish. There are lot of zebrafish in my laboratory because I am a geneticist and I study how mutations occur which is how cancer occurs and I use pigmentation to detect those mutations. By chance the light colored skin of fish I use for that research also taught us a lot about how Europeans, how humans became lighter skin. What Professor King discovered was perhaps one of the most important genetic mutations ever found. A single change among billions of coded instructions in zebrafish DNA that reduced black pigment from their stripes. Soon after, this identical genetic mutation was found in fair-skinned Europeans. There was a magic moment in this research when I got back the results which showed the number and the size and the amount of pigment in light skinned zebrafish were all diminished in and the same thing happened in humans when I opened the textbook. Not only did light skinned people evolve from black skinned people, but lighter skinned people whether they are European or Asian were actually mutants of the dark skinned people. This was remarkable because we had only inferred on the basis of circumstantial evidence that this must have occurred in evolution. We didn't have any concrete genetic evidence. Now we do. Two years later Jablonski would have the final proof she needed to piece together the story of the evolution of human skin color. In 1994 in a cave in northwesternspaina group of scientists uncovered the well preserved skeletons of Neanderthals, an extinct species of Hominid (genus Homo). They had similar ancestors to modern humans but evolved separately and migrated out of Africa toeurope. For more than ten years Doctor Carl Lovelies Fox tried to extract DNA from these ancient bones. It was an almost impossible undertaking, but one was to provide the final clue in the quest to understand the origins of human skin color. Finally they were successful in extracting a fragment Neanderthal DNA. One of the genes recovered showed a genetic mutation that suppresses the production of melanin. This means that like modern Europeans the Neanderthals had pale skin. The twentieth century saw unprecedented mass migration across the planet. The sepia rainbow of skin color began to blend and mix like never before. The composition of most cities in the world are filled with people who have come long distances from their ancestral

7 homelands. Throughout the world millions of light skinned people now live in countries with high levels of ultraviolet radiation. And millions of dark skinned people now live in countries where ultraviolet levels are very low. Humans in a sense are out of sync with their natural environments in that there is a mismatch now between pigmentation ultraviolet radiation levels for many people if do not attend to this mismatch there will be increasing health problems. We know that light people getting a lot of sun are subject to more skin cancers. An equally big problem is the problem of people working in indoor environments and not enjoying any ultraviolet radiation at all during the year. In this day and age, we have been taught that you should never be exposed to direct sunlight; that should always wear sun protection. So if you put a sunscreen on with a protection factor of thirty (which is what is usually recommended) it reduces your ability to make vitamin D in your skin by as much as ninety five percent. Children and adults are working indoors more or are playing on the computer more, they are avoiding sun exposure, and that is the major reason for the vitamin D deficiency epidemic that is global in nature. With human populations now constantly on the move, there is little chance that evolution can keep up. The key for our success and well being is understanding where we are in relation to our environment. We have to take personal responsibility and make decisions about the level of sun exposure that we need and if there is a mismatch we compensate using culture, we compensate by diet, or we compensate by covering up. We (need to) make cultural adjustments. Those cultural adjustments include vitamin D and folate supplements, eating the right foods and wearing the right level of sunscreen. What took evolution millions of years to fine tune can now be managed with the help of science. We now have tremendously more knowledge than we did just a decade ago. This allows us to live healthy, happy lives under any condition, regardless of our skin pigmentation. Science has given us an understanding of the importance of human skin color to our evolution, our health and our humanity. But has it given us any insight into the way we see ourselves and each other. Even in multicultural countries likebrazilattempts to classify people by skin color bring to mind the misunderstanding of the past. Story of two identical twins whose African and Portuguese heritage is typical. Their skin created controversy when they applied to enroll in a local university under a quota system for minorities of color. They were classified as different! About 50 genes of human 30,000 genes are involved in determining skin color. People all over the world are genetically speaking almost identical no matter what color our skin color. Science shows that any effort to classify people in unique categories in according to skin pigmentation is a complete fallacy. Science has swept away outdated concepts of race and once and for all shown that while the color of our skin might be the most conspicuous marker of our identity, our differences really are only skin deep.