Infanticide and cannibalism—the killing and sometimes consumption of young—is a brutal phenomenon observed in lions. While this may seem like a breakdown of social order, the act is not random aggression but a highly specific strategy driven by the powerful forces of evolution. This violence is a direct consequence of the intense reproductive competition between males, serving to maximize an individual’s genetic legacy.
The Evolutionary Imperative: Reproductive Strategy
The primary reason for infanticide in lions is a calculated male reproductive strategy to accelerate the opportunity to sire their own offspring. Male lions typically exist in coalitions and only hold tenure over a pride for a relatively short window, often lasting only two to three years before being displaced by a younger, stronger rival coalition.
A lioness nursing cubs remains in a state of reproductive suppression. Lactation triggers a hormonal state that prevents ovulation, and the female will not be receptive to a male until her cubs are weaned, a process that can take up to 18 to 24 months. By eliminating the current litter, a new male immediately stops the female’s lactation period, causing her to return to estrus in a matter of weeks or a few months.
The act of infanticide ensures that the male is not investing his limited time and energy in protecting and defending the offspring of a rival male. Studies show that a female who loses her cubs to an incoming male and then mates with him gives birth a median of 110 days earlier than if she had lost the cubs under other circumstances and then conceived with the same male. Approximately one-quarter of all cub mortality in the first year of life is attributed to infanticide, demonstrating its significant role in the species’ demography.
The Social Context of Infanticide: Who is the Perpetrator?
Infanticide is intrinsically linked to the social structure of the lion pride and the process of male turnover. The perpetrators are almost exclusively the new coalition of unrelated males that have successfully ousted the previous pride males. These immigrating males target any cubs that are still dependent on their mother, typically those under nine months old.
The resident male fathers, by contrast, are fiercely protective of their own cubs, which is why the most dangerous period for a young cub is immediately following a successful pride takeover. Lionesses recognize this threat and engage in counter-strategies to protect their young, such as hiding their cubs away from the pride for days or weeks after a new male arrives. When a direct encounter is unavoidable, the mothers will often mount a vigorous, aggressive defense, though their efforts often fail against the combined strength of a male coalition.
Lionesses also employ a behavioral counter-strategy by engaging in heightened sexual activity with the new males, often mating with multiple individuals. This frequent, non-conceptive mating, sometimes leading to a period of temporary infertility, serves to confuse the paternity of any future litter, reducing the likelihood of infanticide.
Secondary Causes and Resource Scarcity
While the male reproductive strategy is the overwhelming cause of infanticide, less common scenarios involving cannibalism and resource scarcity also occur, often involving the mother herself. Maternal infanticide is a rare but documented behavior where a mother kills her own offspring. This is distinct from the male’s motive, as the female’s action is usually a tough biological decision about resource allocation.
A lioness may abandon or kill a cub that is severely ill, deformed, or significantly weaker than its littermates. From an evolutionary standpoint, the mother is cutting her losses by withdrawing maternal energy from a cub with a low chance of survival and redirecting those resources to her healthier offspring. When cannibalism occurs in this context, the consumption of the cub serves as a method of resource recovery, allowing the mother to regain the nutrients and energy she invested in the failed offspring.