Why we go bald: an evolutionary hypothesis
Pattern baldness (PB), also called androgenetic alopecia, is characterized by a progressive patterned hair loss from the scalp, which begins usually during the twenties or thirties (Odom et al., 2000). PB was initially thought to occur as a result of shaving (Blaine, 1899). Because frequent use of the razor was believed to stimulate hair growth, researchers believed that the energetic drain to supply the rapid growth of the beard necessarily caused a weakness in other parts of the body and led to decreased hair growth on the scalp. Currently, it is believed that PB results from a combination of androgen levels and a genetic predisposition (Bertolino & Freedberg, 1987; Odom et al., 2000).
Pattern baldness has never been looked at from an evolutionary perspective. With the recent sequencing of the human genome, much research has focused its attention on finding genes that cause baldness, as well as other diseases such as Alzheimer’s, cancer, heart disease, and even infertility. However, most of those studies have ignored the role that the environment plays in the development of disease, and they overlook the importance of looking at the disease from an evolutionary approach. How can a gene for infertility possibly persist in our population at such a high rate? Why would a gene for cancer not be weeded out by natural selection? Some of these problems can be resolved if we consider the role of pathogens in these diseases. Pathogens are constantly evolving with their hosts: when a host discovers a way to fight the infection of a pathogen, the pathogen will be under great selective pressure to evolve and change its tactics. In a sense, we are involved in a never-ending arms race where neither the host nor the pathogen ever gets the upper hand for too long. This explains the persistence of infectious diseases in a population. However, because most chronic diseases take a long time to develop and do not have a clear pathogenic cause, we often overlook the possibility of infectious causation in the development of the disease. This paper will review the literature on pattern baldness and will attempt to understand it by looking at genetic, infectious, and non-infectious environmental causes using an evolutionary approach.
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Treatment
There are four basic treatments available for individuals afflicted with PB to manage their baldness. The first is simply to do nothing. Because hair is not essential for survival, bald individuals are able to live healthy lives despite their lack of scalp hair. However, baldness has been shown to have negative psychosocial effects (Cash, 1992) so many individuals choose to do something about it. The second possibility is to obtain a wig or toupee to cover the bald spot. A third possibility is hair transplant surgery. This works by transferring hair follicles from one area of the scalp to another. Transferred hairs survive, grow, and retain the same characteristics they had in their original site (Norwood, 1973). It has been shown that occipital hairs that are transplanted onto the scalp maintain their resistance to PB, while scalp hairs transplanted to the forearm miniaturize in synchrony with their neighbors on the scalp (Norstrom, 1979, cited in Sinclair, 1998).
The fourth possibility is to take medication. Currently, there are two drugs in the market aimed at reducing hair loss and promoting hair growth. The first is minoxidil (Rogaine), which does not require a prescription. The product is applied directly to the scalp, and works by “revitalizing shrunken hair follicles and increasing their size,” although the exact mechanism is not known. The second drug is finasteride (Propecia), which is taken orally. It works by blocking the conversion of testosterone to DHT, and thus reduces scalp and serum DHT concentrations. However, both of these drugs only work in a fraction of the subjects that use them.
Conclusions
As I have shown, we are still far from determining with certainty the exact causes of pattern baldness. PB baldness is not simply a consequence of aging, as once thought; instead, it is an inflammatory disorder of the scalp. It is likely that genetic, infectious, and non-infectious environmental causes play a role in the development of the disease. Genetic instructions may code for the production of excess DHT, which enlarges the sebaceous glands and provides a more hospitable habitat for microbes. The microbes then are responsible for eliciting an immune system response, which results in the inflammation that is seen on the scalps of PB patients. Finally, light may further exacerbate the problem by acting on bacteria to produce porphyrins, which also excite the immune system and cause inflammation. It is only by considering all three possible causes for a disease that we are able to fully comprehend its etiology and find ways to treat it, or ultimately, prevent it from developing in the first place.
Further research should be conducted to determine the effects of antimicrobial creams on the progression of PB. As mentioned above, it appears that antibiotics may help in reducing hair loss by reducing the number of microbe flora and reducing inflammation (Piérard et al., 1996). In addition, studies should examine the effects of anti-inflammatory drugs such as aspirin on reducing inflammation of the scalp. Perhaps the combination of antimicrobial and anti-inflammatory lotions with minoxidil or finasteride will result in new drugs that will be more effective in attacking the many causes of baldness.
