Chris - Well the answer is Troy—yes, people are very interested in this very question, and also from borrowing from biology using the venoms from other creatures that have anticoagulant properties. For instance, people are looking at the genes that come out of leeches. They’ve got a drug now called Hirudin which is a protein that stops blood coagulating by stealing what leeches use. This same thing could be used because we are always looking for ways to thin blood in a slightly less damaging way than using things like Warfarin, which does have side effects. So I suspect that there are certainly scientists right now who are looking at that very question.

Chris - It was a good question and we think inevitably it’s down to overactivity of some elements of the immune system and some people make more of these gene products, that are being discussed between Ben and Paul Martin there, and it could be that this leads to more inflammatory response at the site of the wound, therefore more production of fibrous tissue by those fibroblasts and that’s why you get more scar tissue. Of course you mustn’t ignore the fact that if you get an infection in the wound as well this can prolong the time it takes the wound to form and that again encourages you to make more fibrous tissue.

We put this to Nina Jablonski

Yes, there is a great contrast. Swedes evolved lightly pigmented skin and light eyes, and due to a different set of genetic changes, people living at the same latitude, the Inuit people, in far North Eastern Asia and in Alaska have actually darker skin than we would predict, and dark hair. Now the dark skin is very interesting because they Inuit experience very, very, high levels of reflected ultraviolet radiation—long wavelength ultraviolet radiation—from the snow. So their dark skin actually protects them from this high amount of UVA radiation. Their dark hair, we’re not exactly sure, but almost certainly the dark hair of Eastern Asian Peoples was a consequence of small population effect; the genetic drift in the ancestors of all East Asian Peoples.

Chris Smith:  So Nina, with that in mind, do you also see increased pigmentation or re-pigmentation amongst seafaring people, because of course they’ll get the incident radiation off the water surface?

Nina Jablonski: Yes, and in many of these seafaring peoples are naturally very dark and they have an excellent potential for making more pigment in their skin. So yes, we need more genetic studies of these people so that we can better understand how their pigment systems work.

Do seafaring people have dark skin?

Nina Jablonski: Oh! But we weren’t. About 50,000 years ago we were not wearing clothes. We probably had the ability to drape some skins over our bodies, but we certainly didn’t have sewn clothes until about 14,000 years ago. So basically we were mostly naked; and occasionally covering ourselves up. One of the ways in which we kept warm also was we had a vigorous shivering response, so we would be able to huddle together, and shiver together to stay warm at night. But clothes came very late in human evolution.   

Chris Smith:  Ideal for The Naked Scientists.

Nina - A basal level of tanning is a bit problematical because it costs a lot (in terms of your body)  to make melanin. Melanin is a big pigment and where you need it. For instance, if you live in equatorial Africa you really need it. It’s worth the expense. If you live outside of the tropics where there isn’t a lot of sun then it doesn’t pay off and so that’s why in some populations you have the ability to tan but in very northern, Eurasian populations you don’t have the ability to tan at all. There’s so little UV. Basically, the body economises.

Nina - Well, it’s a big question and one can argue that there are no such things as human races, because human races are basically defined by us socially. When you go to Britain or the United States or Brazil or India there would be different groups that would be defined as different races. In many respects races don’t exist. What we do see are lots of patterns or genetic variation. Some of these patterns are related to our appearance but those are just a tiny fraction of our genes that actually contribute to these differences in appearance. We have tremendous amounts of variation that don’t coincide with these classic racial groups that have been defined in various places. The long and short of it is races are an outdated, ancient construct that we’d best ignore.

Nina -  Beta carotene probably has some beneficial effect by preventing damage to collagen as opposed to protecting as a sunscreen, per se. Because beta carotene, the precursor of beta carotene (retinoic acid) does influence collagen production in the skin. Taking beta carotene could, in fact, have some beneficial effect  on stimulating collagen formation. Really, you don’t want to get out in the sun and get that much ultraviolet radiation so that this reaction has kicked in, in the first place. You should protect yourself from the sun except for  short or moderate lengths of exposure. Don’t  bask in the sun.

Nina - The rate at which Africa is moving south is very slow. I doubt that this really would have affected human evolution. The timescale of human  evolution is very short compared to the timescale of movement of the African continent.

Nina - There is considerably more UV at the equator and considerably more UVA than UVB. UVA is the type of ultraviolet radiation that begins the process of vitamin D formation in the skin. There’s a lot more UVA as well. At the equator you get bathed, absolutely drenched in UV. And it’s quite a bit hotter. At other latitudes you get considerably less ultraviolet radiation, especially the short length UVB.

Chris -   I guess we can ask this in two ways:  One is - Where do different blood groups come from?  And is there any evidence that eating a certain diet, if you have a certain blood group, has any kind of physiological evidence that it's any use?

Nina -  Well blood groups, of course, are related to the types of antigens, these proteins present on the surface of our red blood cells.  We have, for instance, high concentrations of A blood type in Europe, O in Asia, B in the Mediterranean area and so forth.  The problem is that you find lots of geographic heterogeneity in blood types, and so if you go to the circum-Mediterranean for instance you'll find not only B blood types, but A and AB and O as well.  And so the idea of there being pure blood types in any one area is not very good.  And, perhaps the most important thing is because of this these blood type related diets, basically, are rubbish.  In any given geographic area, there will be people with various blood types that will have shared other aspects of their environmental history.  For instance, many people living in Britain today, there will be a moderate percentage of A blood type, but also many other blood types there, they will have shared a common agricultural background, eating dairy products and so forth.  Lets say if they have O blood type, according to the blood type diet they should eat a particular type of diet, but in fact all of those Os, As and ABs all descended from people with a similar farming and dairy background.  That recent experience, regardless of their blood type, is going to be more important to determine what kind of diet they should eat today.

So pay attention to where your ancestors lived, as opposed to what their blood type is.