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LETTERS: John N Burry Cover up and stay out of sun to prevent skin cancer BMJ 2003; 326: 1148-a [Full text]

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Out of Europe?

Marco Procopio   (22 June 2003)

Cover up and stay out of sun to prevent skin cancer

John N Burry   (2 September 2003)

Out of Europe? 22 June 2003
Marco Procopio, Consultant Psychiatrist Priory Clinic Hove, 14-18 New Church Road, Hove, East Sussex, BN3 4FH, UK Send response to journal: Re: Out of Europe?	Editor-The letter sent by Dr JN Burry reiterates a very important public health message which has our full support. There are anyway some comments we would like to make on the author's interpretation of the connection between the evolution of skin colour in Homo Sapiens and melanoma (1). It is not accurate to say that people with black skin have been “chosen” by natural selection to live in Australia because they are protected against skin cancer, while there are people “chosen” to live in Europe which are not protected against skin cancer when they live in Australia. It is true that dark skinned people are less likely to develop melanoma than fair skinned subjects, but the fact that the aboriginal population in Australia is dark skinned is just a fortunate coincidence and there is no evolutionary connection between skin colour and cancer. Homo sapiens evolved dark skinned in Africa and all living people originate from a common ancestral group in Africa (2). This original group started to spread and reached Europe and Australia through Asia. Both migrations happened around the same time, 40-50,000 years ago (3). In Australia there was no selective pressure to change skin colour, and therefore the Australian aboriginal population remained dark. In Europe, instead, selective pressure started to favour individuals with genes for lighter skin. The factor favouring this population change was not the resistance to skin cancer. Malignant melanoma, in fact, kills usually in the latter part of life, after the sufferers have procreated, therefore passed on their genes. Resistance to melanoma is therefore not an effective mode of selection because it does not affect significantly the reproductive fitness of its victims. The likely factor in the pressure to select individuals with lighter skin amongst the population which expanded into Europe was instead the effect of skin pigment on vitamin balance. Vitamin D can be synthesised only in the presence of Ultra Violet (UV) light and African skin transmits only one tenth of the UV light that can pass through the skin of a white person. Individuals migrating from Africa to Europe started to develop vitamin D deficiency and rickets, which affected their reproductive fitness greatly. Individuals who carried genes for reduced skin pigment must therefore have been favoured as humans spread from Africa to Europe leading eventually to a population with lighter skin (4). The fair colour of the skin of Northern Europeans is therefore the result of the increased reproductive fitness in people with genes for lighter skin at those latitudes. The fact that their skin colour makes them more vulnerable to develop skin cancer in Australia is another story which has nothing to do with evolution. 1. Burry JN. Cover up and stay out of sun to prevent skin cancer. BMJ 2003; 326:1148. (24 May.) 2. Wilson AC, Cann RL. The recent African genesis of humans. Scientific American 1992; 266:22-7. 3. Kirk R and Szathmary E. Out of Asia: Peopling the Americas and the Pacific. Canberra: Australian National University 1985. 4. Jones S, Martin R, Pilbeam D. (Eds) The Cambridge Encyclopedia of Human Evolution. Cambridge University Press 2002. Competing interests:   None declared
Cover up and stay out of sun to prevent skin cancer 2 September 2003
John N Burry, Retired South Australia 5000 Send response to journal: Re: Cover up and stay out of sun to prevent skin cancer	Editor-I have just returned from a prolonged holiday in Europe where I experienced the heat wave and was conspicuous in my hat. Dr Procopio alleges that I wrote that people with black skin have been chosen to live in Australia because they are protected against skin cancer. I wrote that black people were chosen by natural selection to live in Australia but did not say why. Fifteen months after I had begun my systematic enquiry, I happened to read for amusement Malthus on Population, and being well prepared to appreciate the struggle for existence which everywhere goes on, from the long-continued observation of the habits of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. Aboriginal Australians have succeeded in the struggle for existence for at least 60,000 years because they were able to hunt and gather. Aborigines would not have survived if their skins had not been black in Australia’s intense sunlight. Dr Procopio presumes that when Australian Aborigines arrived in Australia their skins were black already. It matters little what the colour of their skin was when they arrived, whether their skins were or became black. Australian conditions composed the Darwinian selective forces which ensured that they were fully protected against sunlight by their black skins, which Europeans who have been chosen by natural selection to live in Europe are not, when they live in Australia. Europeans in Europe depended upon food in their struggle for existence. Vitamin D was essential if they were to survive and it is reasonable to postulate that that accounts for the colour of their skin even although again we can not be certain what the colour of their skin was, when they arrived in Europe. John N. Burry, retired dermatologist PO Box 7177, Hutt Street Post Office Competing interests:   None