Red Hair Non-Expert
Red hair is (not) dying out
A lot of people email me asking about red hair. What is it due to, and what are the genetics underlying red hair. The following is meant as a summary. Inevitably I have simplified and shortened certain aspects so professional geneticists might disapprove of some of the phrases I have used but, in essence, I think it is pretty accurate.
Skin and hair pigment is made up of different types of melanin. There are two broad groups of melanin, eumelanin, which is brown/black , and pheomelanin, which is red/yellow. Somebody with dark hair will have predominantly eumelanin. Somebody with very bright red hair will have relatively little eumelanin but lots of pheomelanin. People with auburn hair will have some of both.
Skin and hair colour often go together, but not always. For instance, people with red hair are usually fairly pale skinned, they don’t tend to tan, they burn in the sun and are more likely to have freckles. There are exceptions however to this rule. Some people, with apparently jet black hair, also have very pale skin and freckle. We don’t understand the latter group very well.
Several years ago, I and colleagues, discovered that the melanocortin 1 receptor, a protein encoded by a gene previously discovered in mice, was responsible for the production of red hair in humans. Everybody has two copies of this gene but there are slight changes in the gene that are very common in European populations. If you have one of about four or five common changes in this gene and, one of these changes are found on both of your chromosomes, then you are likely to have red hair.
A little bit of basic genetics; you have two copies of every gene, you inherit one from your mother and one from your father. If both of these genes are different, with respect to the changes that might lead to red hair, then you will have red hair. If however you only have one change, you have an increased chance of having red hair but it is not certain that you will have red hair.
Such a type of inheritance is described to by geneticists as an autosomal mode of inheritance. This means, in practice, that both your parents may not have red hair, but both could be carriers for the gene for red hair. If this was the case, perhaps one in four of children might have red hair. If one of the parents has bright red hair, and therefore carries two of the changes (one on each of their chromosomes), and the other parent is a carrier, then perhaps 50% of the children might have red hair. It is this aspect of genetics, and the mode of inheritance, that explains why hair colour might skip generations.
There are different sorts of red hair. Some people seem to have what we call “strawberry blonde”, some bright red and some auburn. As far as we know, the genetics underlying these differences are fairly similar, in that changes in the gene referred to above, seem to be important for all sorts of red hair. However, if you have bright red hair it seems you are much more likely to carry two different copies of the gene than if you are a strawberry blonde. We are, however, not completely certain about some of the details in this particular aspect of the work.
There are some other puzzles about red hair. Some men might have red beards but dark coloured hair. This is not entirely surprising as in many mammals the front of the body is a slightly different colour to the back. In some animals, the molecular basis of this is clearly understood, as in these animals, they produce a different protein that seems to have the opposite effects to the red hair gene mentioned above. In man, we don’t think this is the case, but we also observed that people who do have red beards are more likely to carry at least one different copy of the red hair gene.
Another puzzle is why hair colour changes so much during life. Most people are aware that hair colour tends to be lighter at birth and gets darker, particularly during adolescence and puberty. Apart from saying that the cells that produce melanin become more active at this period we don’t understand why this is. Similarly, of course, we don’t really understand greying and lightening of the hair in old age. People with red hair often have different coloured hair at different times of their life. It seems that it is more likely to be red in childhood or in early adult life, than in later life.
One medical importance of red hair is that individuals with red hair are, on average, more likely to burn in the sun and they are at an increased risk of skin cancer. The sensible advice seems to remain that since it is painful and uncomfortable to burn repeatedly in the sun, it is sensible to alter your behaviour such that you don’t suffer the discomfort! On the other hand the risks of skin cancer should also be put in context. For instance if you have red hair, the medical risks don’t compare with the far greater and much more serious risks from smoking and drinking large amounts of alcohol or being grossly overweight.
We don’t know with certainty when the first “red heads” walked the earth but, based on our own research, our guess is around 50-100 thousand years ago. In evolutionary terms, this is relatively recent, and although we can’t be certain, the explanations for the development of red hair generally fall into two groups. The first, is that there may have been some advantage to having red hair and pale skin. One reason for this is that you make vitamin D in your skin, and therefore you are less likely to get rickets (vitamin D protects you against rickets) if you have pale skin and there is not much sunlight around.
An alternative explanation, which some of our own work supports, is that it may have just been due to chance in that, to state it simply, nature may have been fairly indifferent to hair colour in areas of the earth without high sunshine. Diversity may rule!
A link to an article on the Wellcome Trust website is here
Note added 20-8-2007: Some of the above needs to be modified in the light of more recent work. Work on greying has been published in Nature and the weight of evidence perhaps leans towards evidence for selection on MC1R.
Red hair is not dying out!
Nor is blond hair. When I first started work on red hair genes, after the initial publicity following our identification of the gene, I was surprised that every few months the story hit the papers again. I thought it would be a once only story. Journalists put me right: the readers forget, and the same story can be put in a new context every few months.
One story that keeps coming round is the idea that red heads (or blonds) for that matter will die out. My first exposure to this story was via a BBC web page reporting ’some scientists’. Turns out it was a spoof. But still the story resurfaces. The idea seems to be that since red hair is a recessive trait (well almost), as there is more population admixture, the non-red genes will come to ‘dilute’ the red ones. This is a misunderstanding of how genetics works——it is as though we are just mixing pots of paint together and we will never recover what we started with. This is not the case and you need to remember what Mendel thought: genes are discrete entities, that recombine but do not get diluted. Imagine we were talking about height. Just because tall and short people have children does not mean that we all end up the same height.
So, with hair colour genes, as long as possessing red or blond hair does not make you less likely to have viable children capable of reproduction, then the gene for red or blond hair moves into the next generation gene pool. It is not destroyed or altered. Of course, if red hair is assumed to be a recessive, then if it is crossed with non red-hair alleles then the phenotype will not be that of red hair. But the gene in the ‘carrier’ will then go into the next generation and the process will be repeated—the red-headed allele is still there and when it lies opposite another red-headed allele then the person will (well usually) have red hair. We don’t know the gene (or genes) for blond hair but the argument is the same.