The question of whether monkeys consume their young involves complex behaviors studied in primatology. While the concept may seem shocking, the death and occasional consumption of dependent offspring occur in non-human primate societies. These actions are linked to evolutionary strategies concerning reproduction, resource allocation, and social dominance. Understanding this behavior requires examining the biological drivers and varying social contexts across different primate species.
Infanticide and Cannibalism in Primate Behavior
The behavior is distinguished by two actions: infanticide and cannibalism. Infanticide is the intentional killing of a dependent infant by a mature individual of the same species, observed across many primate groups, including lemurs, macaques, and great apes. The most frequent perpetrator is an unrelated adult male seeking a reproductive advantage.
Cannibalism, the consumption of the infant’s body, is far less common than killing alone. When it occurs, it is often secondary to infanticide, though sometimes observed after a natural death. Chimpanzees show the highest rate of post-infanticide cannibalism among non-human primates, where victims are often partially consumed. Most observed cases of primate cannibalism involve the consumption of an infant.
Primary Drivers of Offspring Mortality
The most recognized explanation for infanticide is the sexual selection hypothesis, a male reproductive strategy. In many primate species, nursing females do not ovulate (lactational amenorrhea), preventing conception while they care for an infant. A newly dominant male, often one who has just taken over a group, kills the unweaned offspring of a competitor to terminate the nursing period immediately.
Eliminating the infant accelerates the mother’s return to reproductive cycling, allowing the male to mate with her and sire his own offspring sooner. Documented first in wild Hanuman langurs, this is an adaptive strategy where a male’s tenure as the alpha may be short. The threat posed by infanticidal males is a major evolutionary force, sometimes driving the development of social monogamy where males must protect their young.
Infanticide is also driven by severe environmental or social pressures, categorized as resource competition. When food becomes scarce due to famine or drought, a mother may commit infanticide to conserve energy. This action ensures the mother’s remaining resources are directed toward her own survival or the survival of older, more viable offspring.
Maternal infanticide, the killing of one’s own young, is rare but may involve filial cannibalism, especially where nutrient demands are high. In some capuchin monkeys, resource competition motivates the killing of infants. These instances demonstrate that while male reproductive gain is the dominant driver, ecological stress and the need to allocate limited resources also contribute to offspring mortality.
Maternal Rejection and Species Variation
Negative interactions leading to an infant’s death are not always violent infanticide, sometimes stemming from maternal neglect or rejection. Rejection is a spectrum of behavior, ranging from normal weaning attempts to hostile actions. First-time mothers, or those who had poor early-rearing experiences, sometimes exhibit higher rates of premature or inappropriate rejection.
When rejection is extreme or persistent, especially in high-stress environments like captivity, it can lead to the infant’s death. This behavior is distinct from the evolutionary strategy of male infanticide, focusing on the mother’s individual experience and capacity for care. Early, punitive rejection can also have long-term effects on the infant’s behavior and development, even if it survives.
The frequency of infanticide varies greatly across the primate order, reflecting different social structures and mating systems. The behavior is most commonly reported in multi-male, multi-female groups, particularly among Old World monkeys and apes like chimpanzees and gorillas. However, the behavior is nearly absent in others, such as wild bonobos and orangutans, which have never been observed committing infanticide. This variability highlights that while the potential exists, social organization and ecological pressures determine if these behaviors manifest.