Infanticide, the killing of young offspring, occurs in various animal species, including lions. This behavior is a complex aspect of lion society, driven by biological and evolutionary factors. It reflects a harsh reality of survival in the wild, where individual reproductive success often dictates such actions.
Male Lion Behavior
Male lions frequently engage in infanticide, particularly when a new coalition of males takes over a pride. These new males often kill existing cubs, especially those around nine months old or younger, as these cubs are still nursing. This act serves to eliminate the genetic lineage of the previous pride leaders, preventing the continuation of another male’s genes within the pride.
A primary motivation for male infanticide is to bring the female lions into estrus, or reproductive receptivity, more quickly. Lionesses typically do not become receptive to mating while nursing cubs, a period that can last up to 18 to 24 months. By killing the cubs, the new males significantly shorten this period, allowing the females to become ready to mate again within days or weeks. This strategy enables the new males to father their own offspring sooner, maximizing their reproductive opportunities during their limited tenure, which averages about two years.
Without infanticide, they would spend a significant portion of their short dominance period waiting for existing cubs to mature and for females to become fertile again. The intense competition among males for control of prides and access to females makes this a common strategy.
Female Lion Behavior
While less common than male-driven infanticide, female lions can also kill cubs under specific circumstances, a behavior known as filial infanticide. One reason for this is severe resource scarcity, where a lioness might kill cubs belonging to other females within the pride to reduce competition for food. This action increases the chances of survival for her own offspring.
Female lions may also abandon or kill cubs that are sick, weak, or deformed. This prevents the expenditure of valuable resources on offspring unlikely to survive or contribute to the pride, thereby allowing the mother to conserve energy for future reproductive efforts. In some instances, a lioness might abandon a single cub if her other littermates have died, as investing in a larger litter is generally more reproductively successful.
Evolutionary Significance
Infanticide in lions, particularly by males, functions as an adaptive strategy that enhances the reproductive success of the individual exhibiting the behavior. By eliminating the offspring of rival males, a new pride leader ensures that his genes are passed on to the next generation. This directly increases his fitness, which is the measure of an individual’s genetic contribution to future generations.
This behavior shapes pride dynamics by resetting the reproductive cycle and allowing the rapid establishment of a new male’s lineage. It is a clear example of natural selection at play, where traits that maximize an individual’s genetic propagation persist within the population. Despite its apparent brutality, infanticide can be viewed as a successful, albeit costly, strategy for ensuring the propagation of dominant genes and adapting to the competitive social structure of lion prides.