How Does
Heredity
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While specific genes have not been linked to male baldness, the prevalence of baldness within certain families leads researchers to believe that baldness can be inherited from a man's parents. Baldness is somewhat difficult to pin down in the genetic code, though, and likely is related to more than one specific gene; for this reason, genetic treatments for hair loss may not be possible for quite some time. In addition, common perceptions that baldness is exclusively carried through maternal genes may not hold true, as the complexity of baldness genetics means it is likely passed from both the mother and father of the balding man.
Age
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Although some men begin losing their hair as early as their teenage years, baldness is commonly associated with older gentlemen. The male hormone dihydrotestosterone regulates hair growth and replacement, allowing older hairs that fall out to be replaced; the replacement hairs, though, are progressively thinner and shorter. As more and more hairs fall out, the replacement hair continues to become thinner until it simply stops growing altogether. This steady, predictable loss of hair is commonly referred to as male pattern baldness or male pattern hair loss (MPHL).
Evolution
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Despite the advanced genetic and hormonal research dedicated to identifying causes of baldness, the phenomenon may be an age-old process that served an evolutionary function. Theorists believe that hair loss in prehistoric cultures may have indicated that a man had passed his sexual prime, making him less vulnerable to attacks from other males seeking reproductive partners. The lack of hair also may have served a social purpose, marking a man as more socially developed and a potentially more experienced caregiver to the young.
eHow Article: Why Some Men Go Bald
