Considering how much attention is lavished on the big beasts of the penis world, it seems only fair to spare a thought for nature’s more modest efforts.
Yes, barnacles can extend their flexible penis up to eight times their body length in order to reach potential mates, but what about the other end of the tape measure? Which animal has the smallest penis relative to its size?
- The world's 9 weirdest penises – including a detachable one that swims off after a mate and another that grows back three times
- "It has – proportionally – the longest penis in the animal kingdom. The human equivalent would be a man impregnating his neighbour via the letterbox."
The short answer is: probably the gorilla, at least among mammals.
The slightly longer answer is that this is a surprisingly slippery question. Plenty of male animals do not have a penis in the familiar mammalian sense at all. Instead, they possess a variety of ‘intromittent organs’- structures used to deliver sperm inside the body of a mate.
Most male birds, for example, reproduce by pressing their cloaca [link to “Why some animals have just one hole for everything”] against the female’s cloaca in what is often called a ‘cloacal kiss’. Some fish have modified fins and some octopuses have detachable arms, while spiders use pedipalps loaded with sperm. [link to “The world’s 9 weirdest penises”].
Still, even if we focus purely on mammalian penises, we should probably resist the temptation to imagine a neat global ranking. Zoologists, understandably, have not measured every animal penis and arranged them in a spreadsheet for our convenience. Among the well-studied contenders, however, the gorilla stands out. Or, perhaps more accurately, very much does not.
A fully erect gorilla penis is only about 3cm long. A chimpanzee’s, by comparison, measures about 8cm, despite chimpanzees being much smaller animals.
Male gorillas also have relatively small testes for their body size; one source states that their testes are between 30-35g, compared with about 120g for chimpanzees. For a silverback gorilla, an animal that may weigh well over 150kg and can look as though it has been sculpted from boulders, this is a notably restrained arrangement.
The reason is not that evolution forgot to finish the job, it’s because gorilla groups are usually dominated by a powerful silverback, who typically has privileged access to females. That means there is relatively little sperm competition: the race between sperm from different males to fertilise the same female’s eggs.
Where sperm competition is intense, as in chimpanzees, males tend to evolve larger testes, greater sperm production and, in some species, longer or more elaborate intromittent organs. But, where one dominant male can largely monopolise mating, those pressures are reduced. Consequently, the silverback has invested heavily in size, strength and social dominance to guard access to females, and rather less in hidden plumbing.
It’s perhaps a useful reminder that, in evolution, bigger is only better when bigger helps. For the silverback gorilla, being an imposing mountain of muscle seems to have done the trick. The penis, by comparison, has been allowed to keep a low profile.
