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Did baldness evolve to protect us from prostate cancer? Study


#1

If this is true, its extremely depressing:

Androgenic alopecia may have evolved to protect men from prostate cancer by increasing skin exposure to ultraviolet radiation.
Peter Kabai

Department of Ecology, Faculty of Veterinary Science, AOTK, SZIE, Szent István University, P.O. Box 2, H-1400 Budapest, Hungary

Received 27 July 2007;

Summary:

Androgenic alopecia affects populations adapted to colder climate, and individuals at an age and hormonal status susceptible to prostate cancer. Male pattern baldness enhances absorption of UV radiation on the top of the head, an area directly exposed to sunlight during everyday activities. Ultraviolet radiation is reported to reduce the risk of advanced prostate cancer. Here I propose that progression of androgenic alopecia rather than being a risk factor is a finely tuned mechanism evolved to protect against prostate cancer.

Introduction:

Ethologists perceive androgenic alopecia (AGA) as a social signal evolved to indicate senescence [1], whereas in the medical literature it is discussed as an abnormal benign condition with no physiological effect [2].

Social signal theory has been supported by image manipulation experiments, where pictures of bald men are perceived older than the same faces with full hair [3]. The exact nature of the information conveyed, however, has been debated. Some believe that baldness is a signal of social competence and aggressive dominance [4], others suggest it indicates maturity and a non-threatening form of dominance [1].

In any case, young women perceive bald men sexually less attractive and less active [1]. As AGA affects about 30% of Caucasian males at the age of 30 years [5], signalling senescence at the age of the highest reproductive potential might be premature and therefore costly for many men. Even though the social signal theory has not been incorporated into mainstream medical science, the notion that AGA is not simply a disordered condition but has specific functions deserves attention, considering the genetically pre-programmed nature of the process.

Hair follicles react to androgens in a site-specific manner. In man, with genetic predisposition to AGA, terminal hairs in the temporal and frontal regions and later over the vertex of the scalp are miniaturized into vellus hairs, whereas follicles at other areas are not affected under the influence of androgens. Such differential reaction to the same hormone is pre-programmed in the individual follicles: follicles transplanted from non-balding areas to the bald vertex develop into full hair. Although the mechanism of differential reaction of hair follicles to androgens is not fully understood [6], it is very likely that Type 2 5a reductase (5aR-2) converting testosterone to more potent dihydrotestosterone in the follicles is involved. Besides hair follicles, 5aR-2 is expressed in the prostate, testes, seminal vesicles, and the liver. Inherited deficiency in 5aR-2 activity prevents AGA and results in small prostate. Finasteride, a 5aR-2 inhibitor has been useful in the treatment of AGA as well as prostatic hypertrophy [7]. As changes in the level of 5aR-2 activity affect AGA and prostatic hyperplasia in a similar manner, AGA as a risk factor for prostate cancer has been a target of epidemiological studies. Although findings have been inconsistent, one of the largest study including 1446 prostate adenocarcinoma cases and 1390 controls depicted an association between vertex baldness and prostate cancer [8].

Another line of epidemiological studies suggest reduced risk of prostate cancer associated with sun exposure, outdoor activity, highly active vitamin D receptor variants [9], high level of vitamin D [10], childhood sunburn, regular foreign holidays, sunbathing score, high exposure to UVR [11] or living at lower latitude [12], results all pointing at the protective role of sun exposure.

The hypothesis:

Male pattern baldness exposes a relatively large skin area to sunlight during everyday activity performed in a vertical position. I propose that AGA evolved to elevate UV absorbance and thus to provide some protection against prostate cancer. Moreover, the shared androgen pathways leading to AGA and prostate cancer indicate a finely tuned mechanism of inducing baldness in men susceptible for prostate cancer at an age preceding the predicted onset of the disease. According to this interpretation if baldness is a social signal, then it has gained this function secondarily.

This hypothesis comprises two testable relations. Whether AGA was positively selected for in populations susceptible for prostate cancer can be directly tested when genetic background of AGA as well as of predisposition to prostate cancer are known. Indirect evidence of shared genetic control might be revealed by possible genetic correlations between AGA, sun exposure and prostate cancer in family history studies. The possible protective role of AGA against prostate cancer can be easily resolved. Epidemiological studies on risk factors for prostate cancer should involve questions on AGA status as well as on the level, and surface area exposed to sunlight.

Consequences of the hypothesis:

This hypothesis might be relevant for the design of epidemiological studies as well as for the treatment of AGA and prostate cancer. Epidemiological studies on the link between AGA and prostate cancer can be confounded by the varying level of sun exposure of bald men with high or low outdoor activity, wearing or not wearing a sun protective hat, and living at lower or higher altitudes. Similarly, sun exposure measured as difference in pigmentation between areas protected or not protected from the sun without considering the surface area exposed may weaken the power of testing the cancer-protective role of UV radiation. Controlling for both AGA and sun exposure in both lines of studies might reveal stronger associations between sun exposure and lower risk of non-skin cancers.

Benign prostatic hyperplasia has been treated with finasteride, a potent 5aR-2 inhibitor [7]. As such treatment also halts or reverses AGA, treated men with prostatic hyperplasia might receive less UV radiation during everyday activities than without finasteride treatment. Careful studies are needed so that advice on compensating for reduced sunlit areas could be given to patients. As association between low level of sun exposure with various forms of non-skin cancers, coronal heart disease, and hypertension has been suggested [13,14], links between predisposition to baldness and such conditions would be worthy to seek.

Acknowledgement:

I am grateful to T.O’Keeffe for his valuable comments.

References:

[1] Muscarella F, Cunningham MR. The evolutionary signifi-
cance and social perception of male pattern baldness and
facial hair. Ethol Sociobiol 1996;17:99–117.

[2] Sinclair RD. Male androgenetic alopecia. JMGH 2004;1(4):
319–27.

[3] Henns R. Social perceptions of male pattern baldness. A
review. Dermatol Psychosom 2001;2:63–71.

[4] Keating CF, Mazur A, Segall MH. A cross-cultural exploration
of physiognomic traits of dominance and happiness. Ethol
Sociobiol 1981;2:41–8.

[5] Hamilton JB. Patterned loss of hair in man: types and
incidence. Ann NY Acad Sci 1951;53:708–28.

[6] Trüeb RM. Molecular mechanisms of androgenetic alopecia.
Exp Gerontol 2002;37:981–90.

[7] D’Amico AV, Roehrborn CG. Effect of 1 mg/day finasteride
on concentrations of serum prostate-specific antigen in
men with androgenic alopecia: a randomised controlled
trial. Lancet Oncol 2007;8:21–5.

[8] Giles GG, Severi G, Sinclair R, English DR, McCredie MRE,
Johnson W, et al. Androgenetic alopecia and prostate
cancer: findings from an australian case-control study.
CEPB 2002;11:549–53.

[9] John EM, Schwartz GG, Koo J, Van Den Berg D, Ingles SA.
Sun exposure, vitamin D receptor gene polymorphisms, and
risk of advanced prostate cancer.
Cancer Res 2005;65:5470–9.

[10] Giovannucci E, Liu Y, Rimm EB, Hollis BW, Fuchs CS,
Stampfer MJ, et al. Prospective study of predictors of
vitamin D status and cancer incidence and mortality in
men. J Natl Cancer Inst 2006;98:451–9.

[11] Luscombe CJ, Fryer AA, French ME, Liu S, Saxby MF, Jones
PW, et al. Exposure to ultraviolet radiation: association
with susceptibility and age at presentation with prostate
cancer. Lancet 2001;358(9282):641–2.

[12] Hanchette CL, Schwartz GG. Geographic patterns of pros-
tate cancer mortality: evidence for a protective effect of
ultraviolet radiation. Cancer 1992;70:2861–9.

[13] Schwartz GG, Skinner HG. Vitamin D status and cancer: new
insights. Curr Opin Clin Nutr Metab Care 2007;10:6–11.

[14] Grimes DS. Are statins analogues of vitamin D? Lancet
2006;368(9529):83–6.


I’ll settle for looking good, but I still miss looking stunning.


#2

we’re lucky so? wow


#3

» we’re lucky so? wow

they dont really go into countermeasures or proposals based on their hypothesis. Im guessing take that fish oil (vitamin d) …

Im not really inclined to think they are right however…Ive seen alot of ethiopians and other african tribes with alot of baldness and those guys practically live out in the sun. Ive seen southeast asians on tv that were pattern bald…and there were quite a few of them.

I also keep in mind alot of primates bald—bonoboos, stumptailed macaques, chimpanzees, orangutans…I dont think prostate cancer is a big problem for them either.


#4

» If this is true, its extremely depressing:

I doubt this is true. Baldness has been around since the beginning of the human race. Prostate cancer typically strikes men > 50 years old. The problem is, early humans didn’t live long enough to get prostate cancer. So, prostate cancer wasn’t an issue when baldness came onto the scene.

I think the idea is interesting, but I don’t think it’s specific to one disease, since Vitamin D has many important functions in the body and is now being linked to many diseases.


#5

Funny enough: the guy never uses the word DHT. After all, DHT is the main culprit by attacking hair follicles as much as prostate tissues. So, sunshine drains DHT up from the prostate to the hair and thus prevents prostate cancer… A little weird… Unless he might exhibit a particular chemical reaction that would favor this transfer.


#6

"did baldess evolve to protect us from prostate cancer"
a curious question indeed. Such a question gives evolution a level of reasoning and intellect, which according science, lacks both. If anything baldness works against the male species by lowering his chance of mating and passing on his genes.


#7

n/t


#8

LOL

how the f. this “hypothesis” could be true ? Since prostate cancer appears relatively “late” (e.g., say around 50 yo in average) in the adult life it has no effect whatsoever in reproduction, thus in natural selection. Nice joke! May I suggest another more potent hypothesis, which is that over mastubartion, like thinking jb has multiple names or even that intercytex has gone bankrupt because the game and nathan bought every shares of it and sold it to the irakies, cause the hair to excitate itself and “jerk off” one’s head, which causes irritation and thus shedding, baldness, depression, suicide and the like. What do you guys think ? I’ll give you references if you ask.


#9

youll still prob get an enlarged prostate, plus the bonus of an increased risk of skin cancer on your head.


#10

http://men.webmd.com/news/20100319/early-balding-may-cut-prostate-cancer-risk


#11

no it did not.


#12

» no it did not.

Hairman, take a look at eyikoda’s link. It is very interesting, and the study seems thoughtful.
Also, it is not surprising: if evolution of the species is based on the principle of “survival of the fittest”, this means that balding men are the fittest, as currently, most of men bald in some degree. Baldness is something typical of today’s men.

The non-balding men species got extinguished, and the balding men species survived.


#13

» http://men.webmd.com/news/20100319/early-balding-may-cut-prostate-cancer-risk

Thanks eyikoda!
Very interesting indeed!
The study seems conducted very carefully.


#14

» » no it did not.
»
» Hairman, take a look at eyikoda’s link. It is very interesting, and the
» study seems thoughtful.
» Also, it is not surprising: if evolution of the species is based on the
» principle of “survival of the fittest”, this means that balding men are the
» fittest, as currently, most of men bald in some degree. Baldness is
» something typical of today’s men.
»
» The non-balding men species got extinguished, and the balding men species
» survived.

hehe yea to be fair i honestly didnt even really look at it… :slight_smile:


#15

» » » no it did not.
» »
» » Hairman, take a look at eyikoda’s link. It is very interesting, and the
» » study seems thoughtful.
» » Also, it is not surprising: if evolution of the species is based on the
» » principle of “survival of the fittest”, this means that balding men are
» the
» » fittest, as currently, most of men bald in some degree. Baldness is
» » something typical of today’s men.
» »
» » The non-balding men species got extinguished, and the balding men
» species
» » survived.
»
» hehe yea to be fair i honestly didnt even really look at it… :slight_smile:

I supossed so. :slight_smile:


#16

Natural selection also makes people with worse genetic fitness (athletics, etc) less attractive to the opposite sex. It would be worse for the species if people with bad genetic fitness were just as attractive as those with good genetic fitness.

Some things that are good for the survival of the whole species can still be purely bad for the individuals dealing with it. I would count baldness in this category.


#17

» Natural selection also makes people with worse genetic fitness (athletics,
» etc) less attractive to the opposite sex. It would be worse for the
» species if people with bad genetic fitness were just as attractive as those
» with good genetic fitness.
»
» Some things that are good for the survival of the whole species can still
» be purely bad for the individuals dealing with it. I would count baldness
» in this category.

Exactly but i highly doubt that baldies are the fittest as a genera rule of thumb.


#18

» » no it did not.
»
» Hairman, take a look at eyikoda’s link. It is very interesting, and the
» study seems thoughtful.
» Also, it is not surprising: if evolution of the species is based on the
» principle of “survival of the fittest”, this means that balding men are the
» fittest, as currently, most of men bald in some degree. Baldness is
» something typical of today’s men.
»
» The non-balding men species got extinguished, and the balding men species
» survived.

By that logic, old and wrinkled men are the fittest, because all men become old and wrinkled.

And as for young men, baldness is rare among the young, which shows that going bald young is an unfit evolutionary trait, and so has been selected out.


#19

» » » no it did not.
» »
» » Hairman, take a look at eyikoda’s link. It is very interesting, and the
» » study seems thoughtful.
» » Also, it is not surprising: if evolution of the species is based on the
» » principle of “survival of the fittest”, this means that balding men are
» the
» » fittest, as currently, most of men bald in some degree. Baldness is
» » something typical of today’s men.
» »
» » The non-balding men species got extinguished, and the balding men
» species
» » survived.
»
» By that logic, old and wrinkled men are the fittest, because all men
» become old and wrinkled.
»
» And as for young men, baldness is rare among the young, which shows that
» going bald young is an unfit evolutionary trait, and so has been selected
» out.

that doesn’t make sense at all… prostate cancer is predominant in elderly men… so the fact that baldness likewise evolves at a maturing age, actually speaks in FAVOR of the hypothesis…


#20

What are we calling the “fittest” condition? Is it what is best for the individual, or the best for the species as a whole?

If you have positive traits then it is beneficial if women find you attractive. If you have negative traits then it is beneficial for the whole species (but not for you) if women to find you less attractive.

The majority of women find baldness at least a little bit less attractive than hair. What does this suggest about the merits of baldness?