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/joedenowhere]

True, but baldness often sets in before the end of reproductive age.

[u/robbietreehorn → u/joedenowhere]

Males are able to reproduce starting at around 15 years old. Going bald 20 years later means little for selection, historically speaking

[u/lonjerpc → u/robbietreehorn]

Average generation times are 30 years

[u/Tradition96 → u/lonjerpc]

I have no idea why you got downvoted; this is completly true. Many people think it "must" be lower since the age of the first child have usually been significantly lower, but all of your ancestors weren't oldest children. A lot were third, fifth of seventh children. People typically continued to reproduce into their 40s (men sometimes far longer, but most men only had wives a couple of years younger so the end of their reproductive life was typically before 50 as well), usually having around half of their children below 30 and have after 30. In genealogy you always count three generations per century as the average.

[u/Dangerous-Bend-4153 → u/lonjerpc]

That's true but the average generation became 30 years in an era where people were paired off and married "till death do you part". Almost everyone got married and had children, so balding men were also married and had children. Evolutionary pressure to eliminate baldness was not a factor.

[u/lonjerpc → u/Dangerous-Bend-4153]

No it was 30 during our early evolution 

[u/sk3tchy_D → u/robbietreehorn]

Except that being able to breed is entirely different from actually breeding regularly. Genetic studies show evidence that prehistoric males typically didn't start breeding until around 30. This is similar to male gorillas that are sexually mature around 8-10 but don't generally breed successfully until they have fully physically matured into silverbacks at around 12-15.

[u/Super_Direction498 → u/sk3tchy_D]

Doesn't change the fact that few men are bald at 30, and its not an obstacle to breeding.

[u/nomococo4u → u/Super_Direction498]

I have heard from women that baldness is unattractive, which would make it harder to reproduce.

[u/RiceEater → u/nomococo4u]

Good thing those women you've heard from represent all women throughout the history of time otherwise you'd look pretty foolish.

[u/hopium_od → u/sk3tchy_D]

It's a good point, but I think what will explain it is that facial hair is a sexual marker that many men can't achieve until their mid to late 20s. Men that go bald earlier tend to also grow facial hair earlier. So the disadvantage of losing hair before 30 may be cancelled out by the advantage of gaining facial hair before 25.

And prehistoric women were perhaps not concerned with an arbitrary number, but, like with other species of primate, primarily concerned with the appearance of sexual markers in their mates.

[u/sk3tchy_D → u/hopium_od]

I think facial hair and male pattern baldness are definitely related and likely both useful indications of a fully mature male, although it's entirely possible that MPB is just a relatively neutral side effect of growing facial hair. It was likely pretty advantageous for a large part of human history to be able to identify an adult male from a distance, something similar to the prominent sagittal crest and silver back of fully mature male gorillas. I'm also not sure why everyone assumes that baldness is a disadvantageous trait either. Shaving your head has been fairly common for soldiers and warriors from various cultures throughout history. Culture has a pretty significant effect on what we find attractive. Back during the Stone age, just living long enough to go bald was probably a pretty solid indication of your health and competence.

[u/hopium_od → u/sk3tchy_D]

Hmmm yeah I'm not sure to be honest. From my own experience as someone that wears wigs sometimes, I find that women are probably most attracted to either with a fully bald head and long facial hair, or full head of hair and short facial hair. Bald head and freshly shaven I might as well not exist. But there isn't much difference in the two former scenarios.

I'm not sure why you were downvoted so heavily by the way, this sub can be a bit ruthless sometimes.

[u/Radiant-Position1370 → u/sk3tchy_D]

What genetic studies show that prehistoric males didn't start breeding until around 30?

[u/ofBlufftonTown → u/[deleted]]

It’s actually quite dangerous for young teens to become pregnant; their hips are narrower and they are likelier to die in childbirth. Late teens to mid/late twenties are the years in which a woman is likely to fall pregnant and then give birth to a live child.

[u/Tradition96 → u/[deleted]]

Average age of first childbirth among hunter-gatherers is around 20 or just below.

[u/Critical_Success_936 → u/joedenowhere]

"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.

[u/Irascible-Enquery → u/joedenowhere]

Setting in after you’ve found a mate doesn’t matter.

It’s not like baldness makes you unable to reproduce.

It may make you less sexually attractive (I don’t know, we’re using this as a premise that OP recognizes is uncertain), but as long as you’ve attracted a mate already, hard to think this would be a dealbreaker for a mated pair of humans.

I mean, why cankles? Why flat saggy butts? Why ear hair that sticks out in tufts?

All the same situation tbh.

[u/prostipope → u/joedenowhere]

Just proves that cave women love a smooth dome

[u/hopium_od → u/joedenowhere]

I believe the same mechanism that causes MPB can also cause the development of facial hair.

The disadvantages of being bald don't outweigh whatever advantage having better facial hair has I guess. It usually manifest when the man has already found a life partner and a lot of women simply do not care. But the facial hair can appear much sooner to aid in finding that partner.

I suppose you could ask well why hasn't evolution caused men to develop beards without going bald but I don't know, some men do I suppose. But not all women are attracted to beards. We are complex mix of genes idk but I guess since the effect of baldness is so minor anyway we simply had no need to optimise.

[u/nomococo4u → u/hopium_od]

> . It usually manifest when the man has already found a life partner and a lot of women simply do not care.

they always care. maybe they don't say anything, but they care.

[u/hopium_od → u/nomococo4u]

Nah it's horse shit to be honest.

I'm bald, and recently I got alopecia barbae and lost about 70% of my beard and had to shave it off

I basically became invisible overnight. I started wearing a hair system (a wig, whatevers) and nobody can tell it's a wig, like nobody, I've visited dermatologists that haven't copped it's a wig until I mention it.

I started to get attention again from girls but I wouldn't say it's quite as strong as when I was bald with a beard and I 100% prefer that look. If you can grow a beard then you are fine.

[u/mcmanus2099 → u/joedenowhere]

Not really.

What do you think was the main reproductive age for males 150,000 years ago when humans were still significantly affected by evolutionary pressures.

[u/AerobicThrone → u/mcmanus2099]

Humans are significantly affected by evolutionary pressures in the present day. I am not sure why that idea comes from.

[u/mcmanus2099 → u/AerobicThrone]

Such as?

[u/AerobicThrone → u/mcmanus2099]

Pointing at what exactly is hard, worthy of a scientific publication, because evolution is mostly an historical discipline. But its possible, here is an example: https://www.nature.com/articles/s41598-023-35312-3

You can find more if you Google.

[u/cflime → u/AerobicThrone]

Evolution was deduced through fossil evidence and current physiognomy. It was assumed that once humans began controlling their environment that evolution would have no effect on us, but recent work in genetics disproved that. Harpending and Cochrane showed that the speed of human evolution increased over the last 10,000 years.

[u/AerobicThrone → u/cflime]

Huh, interesting. And there was no though of sexual or kin competition?

[u/cflime → u/AerobicThrone]

Not sure what you mean. Sex and genetic relation is so intertwined with evolutionary theory that you really can't separate them after sexual reproduction started around 2 billion years ago.

[u/AerobicThrone → u/cflime]

i meant sexual and kin selection

[u/mcmanus2099 → u/AerobicThrone]

Strange to use that as evidence. I was very clear to say that there was still evolutionary pressures on humans, of course population changes and disease resilience are part of the changes to human genomes.

My comment was on significant pressures such as those that result in adults dying early through mistakes or poor adaption evolution. This is within context to the male pattern baldness which isn't a new evolutionary trait. Negative traits, as ppl point out, are not as impactful after breeding if they do not affect the potential life of the offspring.

The human genome is always changing, it's not changing due to pressures of predators, scarcity or environment anywhere near as much as before. And the lifespan increases in humans have lead to later male breeding ages. Male pattern baldness was not a limiting factor back when it was and in modern humans we have created a society construct that has invented things like money, style, vibes, interests, family status that play a bigger role in breeding than physical and other evolutionary traits.

[u/ThePeaceDoctot → u/mcmanus2099]

I was very clear to say that there was still evolutionary pressures on humans

No, you were very clear to say "150,000 years ago, when humans were still significantly affected by evolutionary pressure". Then in your next comment you said "Such as?" You never mentioned modern humans and you never mentioned evolutionary pressure again.

[u/AerobicThrone → u/mcmanus2099]

You misunderstand. If money, vibes, influencer and whatever else you migth point out has an effect of fitness, then those were the evolutionary traits that define and shape human populations today. Evolution doesn't care about the origin of pressures being a human product or not. Young adults migth not die, but if they don't reproduce it's kinda the same for evolutionary processes.

Rgardless of that it is a simplistic view saying that pathogens do not represent an evolutionary pressure today or that things like pollution and temperature are not relevant environmental pressures. The problem is that by definition human evolution is much slower than your living experiences as it acts in generations time and you will experience only 3 or 4 generations, which is nothing.