Male gorillas, like all male primates, do possess testes. The gorilla is the largest of the great apes, yet a common point of confusion arises from the relative invisibility of its male reproductive organs, especially compared to its massive, imposing physique. The anatomical structure is present and functional, but the size and prominence of the testes are dramatically reduced in relation to the animal’s body size, a biological outcome tied to the species’ unique social and mating system.
Testicular Anatomy and Location
The testes of a male gorilla are external, positioned within a scrotum, just as they are in humans and most other mammals. However, their visibility is significantly lower than in many other primates. The external location is necessary for spermatogenesis, the process of sperm production, which generally requires a temperature slightly cooler than the core body temperature.
The primary function of the testes is the production of sperm and the secretion of androgens, primarily testosterone. Testosterone is the hormone responsible for developing and maintaining male secondary sex characteristics, muscle mass, and aggressive behavior. Despite the silverback’s immense size, the testes themselves are remarkably small. The average weight of a mature male gorilla’s testes is only about 30 to 35 grams, which is disproportionately small for an animal that can weigh up to 450 pounds.
For context, the testes of a male chimpanzee, less than half the body weight of a gorilla, weigh an average of 120 grams. Even human testes are three times larger than a gorilla’s when measured relative to body weight. This anatomical data suggests a profound difference in reproductive investment driven by evolutionary pressures.
The Evolutionary Reason for Relative Size
The significant variation in relative testicular size among primates is explained by the theory of “sperm competition.” This concept describes the evolutionary pressure that arises when a female mates with multiple males within a short period, leading to a race among the sperm to fertilize the egg. Species facing high sperm competition evolve larger testes to produce greater volumes of semen and more sperm.
Gorillas practice a polygynous social structure, where a single dominant male, the silverback, monopolizes exclusive breeding access to a group of females. This social system means that the silverback’s sperm rarely faces competition from other males. Because the competition takes place outside the female’s body, primarily through physical dominance and intimidation, there is no evolutionary advantage to producing a massive quantity of sperm.
This lack of internal competition has resulted in a reduced reproductive investment in the gorilla lineage. Producing the cellular machinery for large-scale sperm generation is metabolically costly. Consequently, the gorilla has evolved to have the smallest testes, relative to body size, of all the great apes. Conversely, chimpanzees, which have a promiscuous mating system, have the largest testes to ensure paternity.
Reproductive Strategy and Sexual Dimorphism
The gorilla’s small testicular size is directly balanced by its enormous investment in physical strength and intimidating appearance, a phenomenon known as pronounced sexual dimorphism. Silverbacks can weigh twice as much as females and possess significantly larger canine teeth and formidable musculature.
This massive physical investment serves to maintain the silverback’s reproductive monopoly, preventing other males from challenging his dominance and accessing the females. The silver-gray saddle of hair on the back signals full maturity and reproductive fitness, acting as a clear visual display of dominance. The large bony ridge on the top of the skull, called the sagittal crest, develops in mature males; this structure anchors the powerful jaw muscles needed for aggressive displays and fighting.
Testosterone, produced by the small testes, drives the development of these secondary sex characteristics, which are the true weapons in the gorilla’s reproductive strategy. The male gorilla invests in traits that ensure he wins the pre-copulatory competition, making large-scale sperm production unnecessary. The evolutionary trade-off is clear: the gorilla maximizes its reproductive success through sheer body mass and strength, rather than through sperm volume.