Why does Gorilla have small penis compared to humans?

[John Harmonic]

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!

[mistermack]

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. 

[J.C.MacSwell]

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.

[MigL]

My gorilla friend says...

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

What, I'm gonna disagree with a gorilla ?

[CharonY]

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.

[mistermack]

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.