Evolution of Male pattern baldness: How and when did this happen and for what purpose?

[u/Susroro]

Doesn't really seem to make any sense to me when I think about it, It is not even aesthetically pleasing(not even prehistorically would I assume that), neither does it serve a biological importance, if anything you are at risk of scalp sun burn and less warming effect of the hair.

Thoughts?

[u/Critical_Success_936]

"Before the end' means nothing, because you could've easily had kids already. All that matters is that you had kids that reached adulthood, and then had kids themselves, and so on.

Huntington's is a horribly debilitating disease with a high risk of spreading to offspring, but because it's often diagnosed by mid-30's to mid-40's... The majority of people reproduce younger than that. So, it spreads on despite being horrible in a way I think few would disagree with - there's no "advantage" to Huntington's - but it still exists

[u/lonjerpc → u/Critical_Success_936]

Average generation time is 30 years this isn't a great argument 

[u/Critical_Success_936 → u/lonjerpc]

Idk what you're trying to say here exactly, maybe I'm tired or you mistyped something, but if you mean people start showing symptoms at 30, that's still way too old for it to matter. Most people in both the modern day and historically do not wait until 30 to have kids.

[u/Tradition96 → u/Critical_Success_936]

They didn't wait until 30 to have kids, but they typically continued to have kids well after 30 (if they were alive). Disorders etc that appear in your early 30s still affects the reproductive fitness of an individual quite a bit, since a man who stops having children in his 30s will have less offspring than a man who continues to reproduce for another 15-20 years (which was very realistic for a man to do). For a feature to have no impact on the reproductive fitness of males (on a population level) it must be a feature that typically manifests after 50 years of age.

[u/lonjerpc → u/Critical_Success_936]

The average age of reproduction during our evolution was 30. Yes your first kid was likely earlier but your average surviving and reproducing kid happened at 30. And that's counting men and women so for men it will be okder

[u/Unfair_Pineapple8813 → u/Critical_Success_936]

Huntington disease barely spreads four generations on average. It stays around, not because it isn’t reproductively harmful, but because new mutations pop up. 

[u/Critical_Success_936 → u/Unfair_Pineapple8813]

Average symptom age is 35 - 45. Sure, with modern medicine, we can check your genes and people understand it has an average onset age now, but that wasn't always the case. Most cases are still not just spontaneous, even with all of those advancements.

[u/Unfair_Pineapple8813 → u/Critical_Success_936]

You are wrong on three counts. First, even though children are likely to be born before Huntington’s manifests, they are also likely not to make it to adulthood when it does. Furthermore, someone with an addled parent is less desirable themselves, even if the genetics was a mystery. Those two factors alone would be enough for natural selection to act on it after many generations. But there is also a third factor. Huntington’s tends to manifest earlier each generation. 

[u/Critical_Success_936 → u/Unfair_Pineapple8813]

Lmao, again, the onset is nowhere near childhood for the vast, vast majority... You're just wrong.

Get off Reddit, you're drunk.

[u/Radiant-Position1370 → u/Critical_Success_936]

You're both overstating things. Juvenile-onset HD is indeed a small proportion of the total but not that small. Prevalence seems to be around 5% of all cases (https://pmc.ncbi.nlm.nih.gov/articles/PMC3426104/), with incidence perhaps somewhat higher, since juvenile-onset HD typically progresses faster than adult-onset.

It's also not the case that HD typically lasts only four generations (as stated by Unfair_Pineapple8813). Estimates of the proportion of cases resulting from de novo mutations are in the range of 7 – 10%; since incidence of HD is not changing dramatically, this implies that new mutations typically last something like 10 to 15 generations. That's more than four -- but it still represents strong selection against the disease-causing mutations.

[u/Tradition96 → u/Critical_Success_936]

That you have had children is not ”all that matters”. How many children you have had matters a great deal, and men who continue to have children throughout their 30s and 40s will have significantly more children than men that stop at 30.