Female spotted hyenas are generally larger and more muscular than their male counterparts. This is a rare example of reversed sexual dimorphism among mammals, where the female exceeds the male in physical size and strength. The unique biology and intense social environment of the spotted hyena (Crocuta crocuta) drove the evolution of this physical disparity. Female dominance is supported by the physical advantages of greater size and robust musculature, affecting every aspect of hyena life, from their social structure to their reproductive biology.
The Factual Difference in Size and Weight
Female spotted hyenas possess a body mass that is consistently greater than males. An adult female typically weighs between 55 and over 70 kilograms, making them notably heavier than males, who usually range from 45 to 60 kilograms. This difference means that females can be 10 to 15 percent heavier and more robustly built than males of the same species. While both sexes stand at a similar shoulder height, the female’s overall build is more massive.
The greater size is coupled with a more muscular physique, which contributes to the female’s greater strength and aggression. This pattern of female-biased size difference is consistent across various populations in sub-Saharan Africa. Even in captive populations where diet is identical, females still grow larger than males, suggesting a genetic basis for this dimorphism.
Evolutionary Drivers of Female Size and Dominance
The evolution of larger, more dominant females is closely linked to the intense competition for food resources in the hyena’s environment. Spotted hyenas possess massive skulls and jaws that allow them to crush and digest bone. However, this capability takes several years to develop fully in young hyenas. Cubs are completely reliant on their mothers for milk and soft meat until their own powerful jaws mature.
This extended period of dependency places significant pressure on mothers to secure high-quality food, especially at fresh kills. Selection favored females who were large and aggressive enough to dominate males and rival hyenas at a carcass, ensuring their young received enough sustenance. Over evolutionary time, this environmental pressure drove the selection for increased female size and aggression.
Female hyenas are exposed to elevated levels of androgens, such as androstenedione, prenatally, which contributes to their masculinization. This early hormonal exposure influences the development of their aggressive tendencies and contributes to their robust physical build. The masculinization is also responsible for the female’s unusual external genitalia, known as a pseudo-penis. The combination of physical size and hormonal influence provides females with the necessary tools to maintain their control over resources and social rank.
The Matriarchal Social Structure
The physical advantage of the female directly translates into a strict social hierarchy within the hyena clan. Spotted hyenas live in a complex matriarchal society where all females are dominant over all males. The lowest-ranking female in the clan is still socially superior to the highest-ranking male. This dominance is hereditary, meaning cubs inherit their mother’s social rank immediately upon birth.
Female hyenas form lifelong alliances with their relatives, which reinforces their collective power within the clan structure. Males typically disperse from their birth clan once they reach maturity and must join a new clan at the very bottom of the social ladder. Lacking the support network of female relatives, immigrant males are socially submissive and must work to gain favor with the females.
This social order dictates access to food, with females and their young eating before any of the subordinate males. Dominant females often initiate aggression and have priority access to resources and resting sites. The females’ size and social backing ensure that the clan’s resources are primarily channeled to the mothers and their dependent young.