What is the evolutionary reason for humans to have large penis compared to Gorillas and for Gorillas to have small penis that is only about 4 inches long? Btw Gorillas are my favorite animal!

The Gorilla is the normal one. It's we humans that have an unusually large one. Nobody knows for sure why. 

It might be that peeing standing upright is easier to control with an extra inch or two. Or it could be that in hand-to-hand fighting, a bigger penis is more vulnerable. Humans carrying weapons are less likely to bite or get bitten in a fight.

Or it could be that Gorillas establish mating rights by being the dominant male of a harem, and females don't get much of a choice, so the big Silverback doesn't need to attract females, he basically acquires them by combat. We humans tend to pair off, and females get more say in the matter.

Maybe the human female is built differently, due to having to give birth to babies with enormous heads, so human males need a few more inches. 

Or it could be something else entirely. Nobody knows. 

12 minutes ago, mistermack said:

The Gorilla is the normal one. It's we humans that have an unusually large one. Nobody knows for sure why. 

It might be that peeing standing upright is easier to control with an extra inch or two. Or it could be that in hand-to-hand fighting, a bigger penis is more vulnerable. Humans carrying weapons are less likely to bite or get bitten in a fight.

Or it could be that Gorillas establish mating rights by being the dominant male of a harem, and females don't get much of a choice, so the big Silverback doesn't need to attract females, he basically acquires them by combat. We humans tend to pair off, and females get more say in the matter.

Maybe the human female is built differently, due to having to give birth to babies with enormous heads, so human males need a few more inches. 

Or it could be something else entirely. Nobody knows. 

I wonder if the wearing of protective clothing, or having the option of wearing clothing may have something to do with it? The gorilla's might be more vulnerable in that respect.

My gorilla friend says...

"Its not the size; Its how you use it."

What, I'm gonna disagree with a gorilla ?

2 hours ago, mistermack said:

The Gorilla is the normal one. It's we humans that have an unusually large one. Nobody knows for sure why. 

It might be that peeing standing upright is easier to control with an extra inch or two. Or it could be that in hand-to-hand fighting, a bigger penis is more vulnerable. Humans carrying weapons are less likely to bite or get bitten in a fight.

Or it could be that Gorillas establish mating rights by being the dominant male of a harem, and females don't get much of a choice, so the big Silverback doesn't need to attract females, he basically acquires them by combat. We humans tend to pair off, and females get more say in the matter.

Maybe the human female is built differently, due to having to give birth to babies with enormous heads, so human males need a few more inches. 

Or it could be something else entirely. Nobody knows. 

Most research is supportive of the latter as a factor. i.e. mate selection. Often it is contrasted with erect chimp penis sizes, which are close to human sizes (genitalia display also plays a role). There is also the hypothesis that higher promiscuity could play a role.

On 9/29/2018 at 1:05 PM, J.C.MacSwell said:

I wonder if the wearing of protective clothing, or having the option of wearing clothing may have something to do with it? The gorilla's might be more vulnerable in that respect.

Maybe clothing protected from the cold? A big penis might have been a liability till we began wearing something over it. Upright walking might have exposed it to a chilly wind.

Selection could also happen with promiscuous females, where bigger penises might deposit semen ahead of the semen from a smaller one, or even pump out the semen from a previous partner. 

Chimpanzees have extremely big testicles, (from memory) which might compete with other males by producing large quantities of semen, and flushing out semen from a previous mating.

Gorilla silverbacks, having more exclusive mating rights, don't need to compete in those ways, to the same degree.

On 9/27/2018 at 6:06 PM, John Harmonic said:

What is the evolutionary reason for humans to have large penis compared to Gorillas and for Gorillas to have small penis that is only about 4 inches long? Btw Gorillas are my favorite animal!

I think likely sexual selection? I think a cross penile microbiome analyzation would be quite interesting.

1 hour ago, Sohan Lalwani said:

I think likely sexual selection? I think a cross penile microbiome analyzation would be quite interesting.

Why?

3 hours ago, CharonY said:

Why?

Perhaps it would show the variation and difference in the bacteria that colonize and inhabit 2 similar species penises.

Well, this is the expected outcome, but the question is why that would be interesting, especially given the context of this thread.

Sure seems like sexual selection would be part of the answer. Also, if a male has more lumber to lift this feat of hydraulics and so on would require good health and nutrition and therefore a prominent erection would be a display of overall good condition and likely fertility.

14 hours ago, TheVat said:

Sure seems like sexual selection would be part of the answer. Also, if a male has more lumber to lift this feat of hydraulics and so on would require good health and nutrition and therefore a prominent erection would be a display of overall good condition and likely fertility.

I don’t follow this. In humans, mate selection takes place before sexual activity. Women can’t shop around for who has the biggest todger. They only find out after they have made their choice. Don’t they?

56 minutes ago, exchemist said:

I don’t follow this. In humans, mate selection takes place before sexual activity. Women can’t shop around for who has the biggest todger. They only find out after they have made their choice. Don’t they?

Not if we take evolutionary time scales into account. Considering the equipment of chimpanzees the selective pressure likely happened way before our ancestors thought of clothing. And in those situations they certainly were able to shop around.

On 5/3/2025 at 5:16 PM, exchemist said:

I don’t follow this. In humans, mate selection takes place before sexual activity. Women can’t shop around for who has the biggest todger. They only find out after they have made their choice. Don’t they?

There are publications on bipedalism and sexual characteristics. Upright for a male exposed everything, knuckle dragging for a female does similar.

Don't forget double duty as a tent pole!

Ahoy, Pinball!

2 hours ago, TheVat said:

Don't forget double duty as a tent pole!

Ahoy, Pinball!

Well met Sir!

On 5/3/2025 at 6:16 PM, exchemist said:

I don’t follow this. In humans, mate selection takes place before sexual activity. Women can’t shop around for who has the biggest todger. They only find out after they have made their choice. Don’t they?

It is possible to pretend in spirit and in front of yourself a liberal, and actually be a conservative.. ;)

Sexual activity does not have to result in the begetting of offspring. Unsatisfying sex, is a good indicator that such a relationship has no future. Hence the search for a new partner. I think it is much easier to get satisfying classical sex with a larger partner, because they are simply tighter.

I'm a big fan of first date sex. If the sex is successful, that's when you can start talking about something else and start forming a real relationship.

Months of dating, or even engagement, and then a first wedding night that turns out to be a “nightmare” is a recipe for wasting one's life. For becoming angry, bitter, prone to cheating, etc.

Virginity can be lost only once. No amount of sewing, etc. will change that ;) You cannot expect/demand virginity from your partner if you are not one yourself.

20 minutes ago, Sensei said:

It is possible to pretend in spirit and in front of yourself a liberal, and actually be a conservative.. ;)

Sexual activity does not have to result in the begetting of offspring. Unsatisfying sex, is a good indicator that such a relationship has no future. Hence the search for a new partner. I think it is much easier to get satisfying classical sex with a larger partner, because they are simply tighter.

I'm a big fan of first date sex. If the sex is successful, that's when you can start talking about something else and start forming a real relationship.

Months of dating, or even engagement, and then a first wedding night that turns out to be a “nightmare” is a recipe for wasting one's life. For becoming angry, bitter, prone to cheating, etc.

Virginity can be lost only once. No amount of sewing, etc. will change that ;) You cannot expect/demand virginity from your partner if you are not one yourself.

Having a quick look on the link below and also pointed out by @mistermack sexual dimorphism/harem are linked so you get large males with access to the females.

A large body advantageous for keeping the top spot and a large appendage could be a disadvantage, an injury risk.

There is some sexual dimorphism in humans but not as much as Gorillas. (Males are twice the size)

Plus ancient human species and ancestral primates would have been displaying their penis via upright walking from Lucy's time, so about 3.5 million years ago.

A large penis could have been synonymous with fertility, large breasts and child bearing hips in a female.

A large member would still be at risk of injury, humans and their primate ancestors still had to complete for mates and resources. IF that was what the evolutionary pressure was, it would be a trade off between making the females swoon and making sure you could run and fight without getting caught up in the bush.

https://en.m.wikipedia.org/wiki/Sexual_dimorphism_in_non-human_primates

https://pubmed.ncbi.nlm.nih.gov/11319778/#:~:text=Gorillas%20live%20in%20polygamous%20harem,access%20to%20female%20social%20partners.

Probably for the same reason that human breasts are larger than gorilla breasts.

9 hours ago, LuckyR said:

Probably for the same reason that human breasts are larger than gorilla breasts.

Just lucky I guess... 😉