Lions, like all placental mammals, cannot change gender; their biological sex is permanently fixed at conception by a deeply established genetic mechanism. The interest in this topic stems from the rare appearance of maned lionesses, which are genetically female but display traditionally male characteristics.
Fixed Sex Determination in Lions
Lions follow the standard mammalian XX/XY system for sex determination. A lioness is genetically female (XX), while a male lion possesses one X and one Y chromosome (XY). This genetic blueprint dictates the development of reproductive organs and establishes the individual’s sex from the beginning of life.
Lions exhibit strong sexual dimorphism, meaning there are clear physical differences between males and females. The male is typically larger, heavier, and possesses a mane, a secondary sexual characteristic that signals health and vigor. The development of these male traits is regulated by the hormone testosterone, which is produced at significantly lower levels in females.
The Phenomenon of Maned Lionesses
Despite their fixed sex, a small number of genetically female lions have been observed developing manes and exhibiting male-like behaviors. Documented cases, such as five lionesses in the Okavango Delta of Botswana, show these individuals growing a noticeable, though often less full, mane.
These physical changes are accompanied by behavioral alterations, including scent-marking, roaring more frequently, and mounting other females. The underlying cause is strongly linked to hormonal imbalances, specifically elevated levels of androgens like testosterone. In one captive case, a maned lioness had high testosterone due to an ovarian problem, and the male characteristics receded after her ovaries were removed.
The elevated testosterone levels often result in infertility. Although maned lionesses have been observed mating with males, they do not become pregnant, suggesting the hormonal environment disrupts reproductive function. The source of the excess hormones is hypothesized to be a disorder of the adrenal glands or ovaries, causing them to produce and release male hormones at atypical levels.
Distinguishing Phenotype from True Sex Reversal
The appearance of a maned lioness is a change in phenotype, or observable physical traits, but it is not a sex reversal. A true sex change would require the genetic sex (genotype) to switch, which is not possible in adult mammals.
The maned lionesses remain chromosomally female (XX) and their internal anatomy is female, despite external masculinization. The condition is better understood as a hormonal or intersex disorder, where a genetic female develops secondary male characteristics due to an endocrine malfunction. The masculinization of the lioness is a biological anomaly, not a natural change of gender.