My question of selective pressure still remains. In order for baldness to have gone into the gene pool as you claim as a possible evolutionary change, there must have been selective pressure for it. I think we can all agree that the average woman prefers their men to have a full head of hair over partially or fully bald, that alone points to no selective pressure. Unless you can show somehow that bald men have more reproductive success, or rather had more reproductive success in the preceding generations when baldness started (you would have to figure that out too) to get us where we are now of many men going bald later in life, then it's just not evolution.
Also why would it only happen to men as they age? If it's an advantage and a genetic change rather than a breakdown of hair follicles from faulty nutrition, I would imagine it would be present at birth and they wouldn't go through the normal cycle of growing full heads of hair in their adolescence and early adulthood.
Looking at all the factors I think it's unreasonable to say it's more likely for baldness to be an evolutionary trait rather than just the effect of faulty nutrition. Yes some gene pools tolerate this faulty nutrition for this trait better (Asians in particular) but that doesn't make it genetic, it just makes it like everything else in that your genes determine how faulty nutrition will affect you. That would be like saying because Asians have less colon cancer than Europeans that it's a genetic disease rather than a disease of nutrition. Every disease the modern SAD or grain heavy diet causes affects different gene populations differently, still nutrition is the cause not their faulty genes.
No, we do NOT all agree that the average woman prefers their men to have a full or partial head of hair. As Satya pointed out, women have a wide difference in their views of what constitutes sex-appeal in a Man(much like men), and bald people are also seen as more intelligent, which would be a bonus for some women.
Plus, if all or most women really did view baldness as being so bad, why is it that as much as 1 in 4 men noticeably grow bald in their twenties(NOT in old age) with 3 in 4 growing bald, later on? The only plausible explanation for the 1 in 4 figure for young men is that there must be some reproductive bonus to being bald. And it's also been pointed out that the greater number of androgen receptors you have on the surface of your follicle cells, the more DHT activation is likely to be induced and the more likely it is that your hair will fall out and stay out. The distribution of androgen receptors is thought to be determined almost entirely by your genes.
Re why does it only happen to men as they age:- First of all, baldness is heavily influenced by testosterone, which only becomes a factor in men, around puberty, so that if one assumes fluctuating hormone-levels in the 20s that would explain baldness at that stage(20, not 14 or 18, is actually the age at which both males and females stop maturing, funnily enough). Secondly, a lot of animals go through initial stages such as cocoons or keep certain atavistic characteristics from earlier phases of that species' evolution(eg:- tadpoles becoming frogs), so it.
Here's a most interesting theory re baldness and sexual selection from the web:-http://ask.metafilter.com/69507/How-does-natural-selection-account-for-male-pattern-balding
"One theory, advanced by Muscarella and Cunningham, suggests baldness evolved in males through sexual selection as an enhanced signal of aging and social maturity, whereby aggression and risk-taking decrease and nurturing behaviours increase.(1) This may have conveyed a male with enhanced social status but reduced physical threat, which could enhance ability to secure reproductive partners and raise offspring to adulthood.
In a study by Muscarella and Cunnhingham, males and females viewed 6 male models with different levels of facial hair (beard and moustache or clean) and cranial hair (full head of hair, receding and bald). Participants rated each combination on 32 adjectives related to social perceptions. Males with facial hair and those with bald or receding hair were rated as being older than those who were clean-shaven or had a full head of hair. Beards and a full head of hair were seen as being more aggressive and less socially mature, and baldness was associated with more social maturity.
Here's the abstract from that study:
Both male facial hair and male pattern baldness are genetically based, suggesting that they contributed to fitness. The multiple fitness model provides an evolutionary interpretation of the social perception of male pattern baldness and beardedness in terms of the multidimensional meaning of physical maturational stages. Male facial beardedness is associated with the sexual maturation stage and is hypothesized to signal aggressive dominance. Male pattern baldness, by contrast, is associated with the next stage of physical maturation, termed senescence. Pattern baldness may signal social maturity, a non-threatening form of dominance associated with wisdom and nurturance. We tested these hypotheses on social perceptions using manipulated male facial stimuli. We presented faces with three levels of cranial hair, including full, receding, and bald, and two levels of facial hair, beard with moustache and clean shaven. Consistent with the model, a decrease in the amount of cranial hair was associated with increased perceptions of social maturity, appeasement, and age, and decreased perceptions of attractiveness and aggressiveness. Targets with facial hair were perceived as more aggressive, less appeasing, less attractive, older, and lower on social maturity than clean shaven faces.
So maybe women tend to chase hairy, irresponsible and aggressive young guys, but settle down and raise kids with balding but stable and nurturing men, even though they find them less attractive than men with full heads of hair.
Or male baldness may be associated with another, yet identified trait that is being directly selected, and baldness survives as a tagalong."
Of course, the clincher re the testosterone-genetics theory is that if a man is castrated before or at the very start of puberty, he gets a full head of hair. Castration is the one sure defence against baldness. This blows the whole notion linking baldness and ill-health out of the water. Besides, if one takes the theory of baldness and ill-health too seriously, one would have to assume that Asians were healthier/had healthier diets etc. than other racial groups, which is very unlikely.