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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.

DarcyThomas
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    You need to show some evidence in support of your premise that a trait "looks" selected. – swbarnes2 Apr 20 '18 at 21:21
  • @swbarnes2 I never said "looks" , but I have taken what you on board said and have rewritten to better layout my premise, with evidence for it. – DarcyThomas Apr 21 '18 at 06:43
  • @david Can you please remove the duplicate. As per the 3rd paragraph in this meta post https://biology.meta.stackexchange.com/questions/3116/questions-asking-for-evolutionary-reasons This question is about "specific hypothesis" In other words this is not a 'Why does evolution...' question; but a 'What caused this evolution...' question. – DarcyThomas Apr 23 '18 at 21:33
  • "Appears to have a reason" is not any different from "appears selected". Not every trait you find distinctive has been specifically evolutionary selected for. – swbarnes2 Apr 23 '18 at 22:02
  • @swbarnes2 The question is: there appears to be a reason What is the reason. If you think that the answer is "There is no reason" then put that as a answer and it can be voted on along with other answers of: "The reason is XYZ", "The answer is ABC" – DarcyThomas Apr 23 '18 at 22:07
  • If I pour our some M&Ms from a bag, and I assert that there are a disproportionate number of red ones in the bowl what is the reason? – swbarnes2 Apr 23 '18 at 22:36
  • @swbarnes2 Either "Common cause" or "Special cause". Respectively: Luck (Good or bad depending on your taste in M&Ms) or something (I don't know what, but there is a reason) which is causing the M&M production line to add more Reds than other wise would be expected. "I wonder what the reason is?" How would you work out which of those two options is the actual cause? – DarcyThomas Apr 23 '18 at 22:51
  • I'd be interested if anyone can come up with a plausible evolutionary advantage to male pattern baldness; reduced susceptibility to head lice and lice bourne diseases was the best I could do, but I don't see how it would be selected for when the trait mostly emerges after most of the natural and sexual selection and reproductive successes have already taken place. Mmm, I would also be interested to see a plausible reason why it has to have an evolutionary advantage and cannot be something tolerated. – Ken Fabian Apr 23 '18 at 23:54
  • You aren't understanding. You can't give a meaningful answer to a question if the premises are unfounded. You can't meaningful answer "Why is the sky green and purple stripe" if it isn't actually that color. – swbarnes2 Apr 23 '18 at 23:55
  • @swbarnes2 Would it make a difference if the question was changes to: ... appears to have a reason (assuming that there is one, and it is not just a ransom evolutionary artifact)... – DarcyThomas Apr 24 '18 at 01:18
  • @swbarnes2 What makes you think that the premise is unfounded? (unproven, sure; but unfounded !?!) – DarcyThomas Apr 24 '18 at 01:20
  • @KenFabian I (the OP) have one, but I wanted to give others time to put up other conjectures before mine (so I don't taint their responses) – DarcyThomas Apr 24 '18 at 01:23

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Baldness would appear to be a trait on display. That being said, hair loss can be selected against the opposite condition (full head of hair), or selected by way of precise pattern deemed attractive. So, male pattern baldness evolution for mate selection purposes is probably a factor in play. But, either way, hair loss appears to have both its advantages and disadvantages as far as both fitness and mate selection is concerned.

Similarly, in terms of fitness, the advantage/disadvantage you state is the immediate positive advantage of hair as a protectant. The immediate advantages of hair diminish as one grows older, making age apparent. Old age is disadvantageous in itself (older can mean less fit). Hence, the immediate advantage for a protection against the elements decreases and becomes less relevant to survival as one grows older. Please see the references below.

https://en.wikipedia.org/wiki/Mate_choice

https://en.wikipedia.org/wiki/Evolution_of_ageing

user22542
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  • "Questions like this are in the domain of mate selection (or choice) in biology" - citation needed. It is not at all clear that the answer to OP's question has anything to do with mate selection, unless you can cite evidence that it is. – Bryan Krause Apr 20 '18 at 21:42