The killing of lion cubs by adult lions, known as infanticide, is a behavior rooted in the complex social dynamics and reproductive strategies within lion prides. Understanding the reasons behind this act reveals a harsh but adaptive aspect of their natural world.
Male Reproductive Strategy
The most frequent cause of lion infanticide is linked to the reproductive strategy of male lions. When a new coalition of males takes over a pride, they kill the existing cubs sired by previous males. This serves a biological purpose: female lions do not enter estrus while nursing cubs.
By eliminating these cubs, the new males accelerate the lionesses’ return to fertility, allowing them to sire their own offspring sooner. This ensures their genes are passed on within the limited time they hold control of a pride, often before being challenged by younger males.
This strategy directly benefits infanticidal males by increasing their reproductive success. Research indicates that female lions whose cubs are lost at a takeover resume sexual activity within days or weeks, significantly faster than the 18 months it would take if their cubs survived. This acceleration of the reproductive cycle drives the male’s behavior, maximizing their limited opportunity to reproduce. While lionesses may attempt to defend or hide their cubs, the size and strength of the new males make these defenses unsuccessful.
Other Contributing Factors
While male infanticide is the most common form, other factors also lead to cub mortality, including instances where lionesses are involved. Female infanticide, though rarer, can occur for various reasons. Lionesses might abandon or kill their own cubs if they are unhealthy or weak, focusing resources on healthier offspring or future litters.
A female may also choose to invest in larger future litters if a single cub remains after others have perished, maximizing her lifetime reproductive success. Resource scarcity and environmental stress play a role in cub survival. In times of limited prey or harsh conditions, lionesses may abandon or neglect cubs, which then succumb to starvation or exposure. A lioness struggling to sustain herself may not have the resources to care for her young.
Additionally, accidental deaths and predation by other species contribute to cub mortality. Cubs can die from accidents or fall prey to other predators. However, these instances differ from intentional infanticide driven by reproductive or resource-competition motives.
Evolutionary Persistence
The persistence of infanticide, particularly male infanticide, as a strategy within lion populations can be understood through the lens of evolution. This behavior offers a selective advantage for males by accelerating their reproductive opportunities. By eliminating the offspring of rivals, new dominant males ensure that their own genetic lineage is quickly propagated within the pride. This mechanism ensures that the genes of the most successful males in securing and holding a pride are passed on to the next generation.
From an evolutionary standpoint, this seemingly harsh act is a mechanism for natural selection within the pride structure. It streamlines the reproductive cycle, allowing the new males to quickly establish their genetic legacy. While devastating for the individual lionesses and cubs affected, the strategy has endured because it consistently provides a reproductive benefit to the males who employ it. This highlights how behaviors that enhance reproductive success can become ingrained over generations, even if they appear cruel from a human perspective.