Female Infanticide: General Information
“The instincts of the lower animals are never so perverted as to lead them regularly to destroy their own offspring”
–Charles Darwin in The Descent of Man, and Selection in Relation to Sex
Infanticide in humans may be one of the most detestable actions conceivable, and in animals, the killing of conspecific young seems odd at first glance. Thus,.png)
as the excerpt above from Darwin’s second most famous work implies, researchers originally considered cases of infanticide as isolated, insignificant incidents. Egg dumping in birds along with a few reports of infanticide in langur monkeys and lions had been noted, but the data was unclear. According to biological traditions, behaviorswere originally evaluated based on their value to the survival of the species. By these standards, scientists could only categorize infanticide in two ways: social pathology in which the behavior from a fitness standpoint was unexplainable or as a means of population regulation to prevent overcrowding (Hrdy and Hausfater 1984). Once biologists began to approach infanticide from an evolutionary perspective around 1970, research took off. Infanticide has now been studied in mammals (including humans), birds, fish, amphibians, rotifers, and insects and is now considered to be a widespread animal behavior phenomenon.
Infanticide is defined as, “Any behavior that makes a direct and significant contribution to the immediate death of an embryo or newly hatched or born member of the perpetrator’s own species” (Mock 1984) or the killing of conspecific young. Female infanticide in non-humans occurs when the perpetrator is a female. Some of the terms in this definition are vague; thus, Mock provides clarification: “Direct contribution” can mean physical harm or aggression or parental neglect if the perpetrator happens to be the victim’s mother. In addition, the victim must die as an infant in order for its death to be considered a result of infanticide. Neglect or abuse an infant receives resulting in a premature death later in life does not qualify.
As of 12 years ago, female infanticide had been reported in at least 25 species of mammals (Wolff 1997) and is also prevalent inmany avian species. In certain animals, it can be a major source of infant mortality. In the case of black-tailed prairie dogs (Cynomys ludovicianus), it accounts for the total or partial destruction of up to 50% of all litters (Hoogland 1985). Its occurrence across many animal species signifies that it confers some type of benefit to the perpetrator, and researchers have formulated many hypotheses that describe the exact fitness advantages gained from infanticidal acts. However, the mothers of infanticide victims usually suffer an overall fitness loss; thus, some species have evolved female counter-strategies to dampen its negative impact, including female territoriality (Wolff 1993). Not only is female infanticide widespread, but it also significantly impacts the dynamics of many social systems.
This web page was completed in partial fulfillment of the requirements for Biology 323, Animal Behavior, at Davidson College in the Spring Semester 2009. Any questions regarding the content of this web page should be directed to Dr. Verna Case.
as the excerpt above from Darwin’s second most famous work implies, researchers originally considered cases of infanticide as isolated, insignificant incidents. Egg dumping in birds along with a few reports of infanticide in langur monkeys and lions had been noted, but the data was unclear. According to biological traditions, behaviorswere originally evaluated based on their value to the survival of the species. By these standards, scientists could only categorize infanticide in two ways: social pathology in which the behavior from a fitness standpoint was unexplainable or as a means of population regulation to prevent overcrowding (Hrdy and Hausfater 1984). Once biologists began to approach infanticide from an evolutionary perspective around 1970, research took off. Infanticide has now been studied in mammals (including humans), birds, fish, amphibians, rotifers, and insects and is now considered to be a widespread animal behavior phenomenon.