Re: Is alopecia universalis' frequency increasing and is it a sign of evolution

Hi Fabrice,

Thanks for the interesting questions. I’m not a MD, but as you said, your questions cross several disciplines, so I’ll try and give you an answer from my perspective as an evolutionary geneticist.

In order to address your questions (is AU increasing in frequency; is a change in frequency a sign of evolution in our species; and finally will everyone have AU in 1000 years?), we have to look at the underlying causes for AU.

Alopecial Universalis (AU) is a condition of complete hair loss that seems to affect less than 2% of the general population. As far as I can tell, there are two causes of AU. In the first case, AU is the result of a progressive autoimmune condition known as Alopecia Aerata (AA). AA begins as hair loss in small circular patches on the scalp. This progresses to Alopecia Totalis, in which all of the hair on the scalp is lost, and finally to AU. An autoimmune disease is one that results from an error in the normal function of the body’s immune response. Our immune systems are normally able to distinguish between our own native cells and the foreign cells of pathogens (bacteria and parasites) or cells infected by pathogens (viruses and bacteria), attacking pathogens and infected cells, but leaving our own cells alone. This system is malfunctioning in the case of autoimmune AU, and the native cells of hair follicles are being mistaken for foreign cells and attacked. No one is exactly sure why this happens. It could be because the hair follicles become infected with a pathogen (e.g., a virus) or it could be for a variety of other reasons. There is some evidence of a genetic role in the development of autoimmune AU, as AU is 20 times more common among people who have inherited two defective copies of the Autoimmune Regulator gene (on Chromosome 21). I’m sorry to say that these folks have a lot worse problems than AU, but their AU will go away if they are treated with immunosuppressive therapy. Autoimmune AU will sometimes go away even without immunosuppressive treatment.

In the second case, AU seems to be a genetic condition that occurs in people have inherited two defective copies of a gene that seems to be related to the mouse hairless gene (found on Chromosome 8). Babies born with two copies of this congential AU gene develop little or no hair, and are hairless for their entire lives.

So, you can see that there are two very different conditions that can result in AU. One seems to be at least partially environmental and is potentially reversible; the other seems to be largely genetic and seems to be irreversible. With this in mind, we can get to the business of addressing your questions.

Is the frequency of Alopecia Universalis increasing? As I said earlier, I’m not a medical doctor, but I don’t think so. I’ve looked through the literature and I haven’t seen anything suggesting that the number of cases of AU is increasing. In addition, I sometimes attend conferences pertaining to immunology and genetics, and I can’t recall having heard anyone make this claim. The best thing to do would be to ask a dermatologist, but I don’t think that there is an evolutionary reason for AU to be on the rise (see below). We can always invent scenarios in which the incidence of autoimmune AU could be on the rise. For example, if the trigger for the autoimmune response were a viral infection, then the cases of AU might increase in response to the spread of the pathogen. Again, this seems unlikely. However, if AU is on the rise, it seems likely that it is due to environmental, rather than evolutionary, pressures.

It might be that you have confused other forms of alopecia, androgenic alopecia (aka pattern baldness) and traction alopecia (hair being pulled from the follicle), with AU. Some people believe that pattern baldness is becoming more frequent (but I think that they’ve never been to Mexico City, where every old man seems to have a head of thick white hair) and traction alopecia is becoming more common in communities where heavy hair-extensions pull on the scalp or where the hair is pulled into tight ponytails. Neither of these conditions is the same as AU though.

Can a change in the frequency of Alopecia Universalis be regarded as a sign of the evolution of our species? Yes, it could be regarded as such if it were due to a change in gene frequency, but if it were due to a change in the environment (like the spread of a virus), it would have nothing to do with evolution. A change in the frequency of any gene counts as evolution, because evolution is defined as a change in gene frequencies over time. So for example, if the frequency of the congenital AU gene were to change from one generation to the next, that would an example of evolution. The same thing would be true for a change in the AIRE gene frequency, or a change in the frequency of your favorite gene. Our species is always evolving, because the frequencies of our genes are always changing from one generation to the next. For the most part, the magnitude of these changes is very small, so that the changes in the frequency for an individual gene don’t mean much. It is only when the frequency of a large number of genes changes to a large degree that you begin to see the differences that we associate with evolution.

So, now you must be wondering,” how do these changes in gene frequency happen?” and that brings us to your last question.

Could AA (or AU) be the norm in one thousand years? From an evolutionary point of view, this seems very unlikely to me. I included the caveat that this answer came from an evolutionary point of view because it is always possible that everyone could be infected with the (hypothetical) virus that triggers autoimmune AU in 1000 years, but again, that would not be evolution.

In general, changes in gene frequency result from the actions of forces called natural selection and genetic drift, so in order for everyone to have AU in 1000 years, one or both of these two forces will have to be at work.

Natural selection occurs when one organism contributes more offspring to the next generation than other organisms. In order for natural selection to result in everyone having AA or AU in 1000 years, the people with genes that result in AU would have to consistently contribute more offspring to the next generation than the people without those genes. I can’t really see a plausible scenario in which this would occur. Even if hairlessness became the new standard for mate choice (assuming we could get everyone to agree on a single standard), anyone could use technology to achieve hairlessness. There would be no natural selection for people with AU. Perhaps “suffering from autoimmune disease” could become a new standard for mate choice, but that seems unlikely.

Genetic drift occurs when random events affect a population, resulting in changes to gene frequency in the next generation. However, the larger a population is, the less susceptible it will be to genetic drift. On a very small scale, genetic drift occurs every time someone who can have children decides not to have children. Their genes are not passed to the next generation. One dramatic example of genetic drift is called a founder effect, where a subset of a population founds a colony and brings a subset of the genetic diversity of the original population with them. Some of the genes in the founding population genes are over-represented in the colony, and some are under-represented. Another even more dramatic example is a population bottleneck, where a population drops dramatically in size to a few survivors, who then repopulate the area of the original population. Only the genes of the survivors are represented in the new population. In order for genetic drift to result in everyone having AA or AU in 1000 years, something would have to remove those of us without AU genes from the picture. Given that there are about 6 billion people alive today, I can’t come up with a plausible scenario for this either.

So, to sum up, evolution is the result of changes in gene frequencies from one generation to the next. In order for AA or AU to increase in frequency over time, more people have to be born with genes that result in AU in each generation. Right now, that doesn’t seem to be the case (and I can’t think of any scenarios in which it would be the case (no offense meant to people with AU)). This is also true for the other traits that you mentioned in your question (average height, body proportions, skin hue and skull shape). In order for one particular version of each of these traits to become the “norm” in 1000 (or even one million) years, it would either require that we all adopt one standard for mate choice (unlikely), or that everyone who didn’t have the genes for those traits stop reproducing (even less likely).

I hope that answers your question, Fabrice. For general information on evolution you should take a look at the MadSci Evolution FAQ, and the Talk.Origins intro to Evolution.

In addition, here are some papers that you might want to take a look at for more information on the genetic basis for autoimmune AU.

Tazi-Ahnini R, Cork MJ, Gawkrodger DJ, Birch MP, Wengraf D, McDonagh AJ, Messenger AG. (2002) Role of the Autoimmune Regulator (AIRE) gene in alopecia areata: Strong association of a potentially functional AIRE polymorphism with alopecia universalis. Tissue Antigens. Dec;60(6):489-95.

Akar A, Orkunoglu E, Sengul A, Ozata M, Gur AR. (2002) HLA class II alleles in patients with alopecia areata European Journal of Dermatology May-Jun;12(3):236-9.

Colombe BW, Lou CD, Price VH. (1999) The genetic basis of alopecia areata: HLA associations with patchy alopecia areata versus alopecia totalis and alopecia universalis. J Investig Dermatol Symp Proc. Dec;4(3):216-9.

Keep asking questions!