What Do a Silverback's Penis and Testicles Look Like?
In relation to their body mass, the testicles and penis of a gorilla are not very noticeable and much smaller than in other apes. The testicles of a gorilla weigh 30-35 g, whereas those of a chimpanzee weigh about 120 g; this compares to about 40 g in the human male. The erect gorilla penis is only 3-6 cm long, whereas that of a chimpanzee measures 8-18 cm in length. Chimpanzee males need a longer penis due to the voluminous anogenital swelling of the oestrous females.
Scientists explain these striking differences between the two species with the theory that chimpanzees need to produce a lot of semen because they compete continuously with other males and mate much more frequently than male gorillas. By contrast, in gorilla groups the dominant male usually is the only mating partner for the females, or at least he is the one the females prefer. Not only is the erect chimpanzee penis, with which they court oestrous females, larger than that of gorillas, but its bright colour stands out in striking contrast to their dark pelt. In contrast, the gorilla male's penis is small and black.