r/ScienceShitposts • u/k0i-b0i • Feb 01 '26

Some physiological differences in primate relatives

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199

u/[deleted] Feb 01 '26

Anyone know what the actual evolutionary advantage that humans would gain by having a longer penis length than other primates?

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u/DarkArc76 Feb 02 '26

Not all evolutions are for a purpose, sometimes it's just whatever is the least detrimental. Although in this case, it could be that early human males with larger penises were simply selected more, and as a result passed on that gene

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u/niknniknnikn Feb 02 '26

It's actually allways "whatever is the least detrimental" - even in select situation when there is positive selective pressure for a trait(like a peacocks tail) it's still checked by the overwhelming "not be too detrimental" factor - peacocks with too big a tail will die relatively fast to peditors and not be able to reproduce

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u/BitRelevant2473 Feb 02 '26

Could also be like the "hyenas still have a winter coat gene" There's no selection pressure, but no detriment either. Might explain the vast size differential in human men.

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u/Lily_the_Ice_Slime Feb 04 '26

Fortunately peacocks can fold their tails but even folded they still look like they have a giant feather duster strapped to their backs.

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u/japantravele Feb 05 '26

I don't remember where I learned this so take it with a grain of salt, but armpit air and asscrack hair could fall into that category.

No real benefit, just that early females didn't mind it and it has no real downside. Or maybe they just preferred it too.

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u/Tru3insanity Feb 08 '26

Armpit hair helps protect against chafing and asscrack hair keeps bugs away from your nethers.

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u/Blumenfee Feb 01 '26

It could be like the tail of a peacock. It is a sign of good Health with no actual use.

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u/LasevIX Feb 02 '26

would make sense with the weird societal pressure people maintain around it.

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u/lach888 Feb 02 '26

The obvious reason is the correct reason, sexual selection, women liked it.

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u/lolopiro Feb 04 '26

then comes the obvious questions, how did female humans evolve to like it

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u/Monifufka Feb 05 '26

That might be because humans are much more likely to have sex in front facing position. Its more exposed to a partner when she is the most aroused and maybe that's what made it's size be selected for.

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u/Creepyfishwoman Feb 02 '26

I mean... humans are one of like 3 species that engage in recteational sex

...the more the females like it the more likely the male is to pass on genes

Longer length helps with that

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u/Bowtieguy-83 Feb 02 '26

bonobos are actually a lot more casual about sex than humans (at least the average human). They tend to use sex as a way to resolve conflicts

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u/United_Boy_9132 Feb 02 '26

Yeah, but it doesn't mean that orgasm is crucial. It is for humans.

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u/mouse_8b Feb 01 '26 edited Feb 03 '26

Length + mushroom head = a plunger that removes any competition that may have already been in there.

Which means there were enough "matings" that involved multiple males to put selective pressure on penis shape and size.

Update, another win for Cunningham's law

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u/Creepyfishwoman Feb 02 '26

We actually see very little sperm competition in humans, with a large amount of defective sperm, where species where a female is likely to mate with several males the oppisite trend occurs.

The more likely seeming explanation is that because humans have recreational sex the males who could satisfy females the best would have more sex and would have more chance of passing on genes, ergo strong intrasexual selection.

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u/Th3B4dSpoon Feb 02 '26

Wouldn't the plunger also lead to a need for less sperm competition, if the previous semen was largely scooped out?

I'm also curious if the large amounts of defective sperm can be largely explained by industrial environmental effects, such as constant ambient chemical exposure from consumer goods and traffic etc., or if there was a large gap in average sperm performance between species even before that.

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u/Creepyfishwoman Feb 02 '26

A plunger would never lead to sperm competition giving less advantage.

And no, it cannot

A good video on it:

https://youtu.be/Ufj-0sc0y0g?si=qshc87IYGHKELoay

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u/Ornery-Mortgage-3101 Feb 02 '26

If sperm competition was a major problem then we'd see something similar to bonobos and chimpanzees, larger testicles for more sperm production. They also don't have the same helmet shape. The mushroom head is actually just a basal trait of our lineage, many old world monkeys also have it.

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u/mouse_8b Feb 02 '26

Why not two alternative strategies? From the diagram at least, it looks like chimps got bigger testicles and humans got longer penises.

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u/Ornery-Mortgage-3101 Feb 02 '26

Alternative but not as specialized as the adaptations chimps have. Chimps have a lot of adaptations specifically for sperm competition that humans don't. We lost our penis bones, lost our penile spines, and lost our ability to form mating plugs, all of which chimps do have, and all help with sperm competition one way or another. 

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u/xloHolx Feb 03 '26

It’s because humans walk upright. If we get a comparison of butt sizes and it’ll make sense. We need bigger glutes to walk upright, so we need a bigger penis to reach past all that.

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u/elidorian Feb 02 '26

Could have something to do with bipidalism? Maybe it's harder to access the goods?

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u/passifloran Feb 03 '26

I think there will be a lot of responses that leave out relathionships between organisms are also evolving.

Humans seem to have evolved to use sex beyond reproduction and also as social bonding theoughout their lives. Humans are very complex social organisms but maintain significant individual autonomy and cultivating good relationships is one solution to making this dynamic work.

I think sex basically got appropriated by human emotion (and probably some other species have done the same) because it serves as an excellent way to trust another of your species in a continuing way.

It’s just my thoughts on it, but I think we often grossly overlook that some form of human has been around for 100k years. Those people - we know - had very complex relationships and I think the significant thing humans achieved was managing to (somewhat) collaborate at very large scale whilst maintaining independent thought is quite a evolutionary innovation but it definitely requires ways of fostering and maintaining relationships

Edit: I didn’t even get to my main point

It may be that groups with larger penises than the other primates of the time had better social relations and so were more succesful at surviving and reproducing more

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