This question already has an answer here:
Male pattern baldness is a common genetic trait. With a distinctive pattern/ density gradent (as apposed to general old age thinning as the body ages)
Hair has an advantage of protection from the sun/weather. So to lose it in a distinctive pattern (and lose that advantage) appears to have a reason
*; and as it is a genetic trait, it seems like it would have been something that was selected for (or it would be more likely to be selected out).
So why is it better to develop pattern baldness as someone gets older?
So what might be the biological/evolutionary advantage to developing baldness?
Traits get selected for good and bad reasons(in retrospect), however I am interested in the reason why this particular trait has been selected.
* Lets assume that there is a specific cause (causes) and it is not just a leftover evolutionary artifact.
The related question: Why do some bad traits evolve, and good ones don't? provides some interesting background, but doesn't specifically address the What causes in this question.