Question

Evolution Question.

An old alternative hypothesis for the evolution of infanticide was that parents killed offspring (including their own) when food was short for the good of the group.

On the basis of a modern view of adaptation, why is this not a good explanation for the evolution of infanticide?

Answer 1

According to the modern view, Infanticide is caused by sexual conflict and has the general theme of the killer (often male) becoming the new sexual partner of the victim's parent, which would otherwise be unavailable. This represents a gain in fitness by the killer, and a loss in fitness by the parents of the offspring killed. This is a type of evolutionary struggle between the two sexes, in which the victim sex may have counter-adaptations that reduce the success of this practice.

Infanticide only came to be seen as a significant occurrence in nature quite recently. At the time it was first seriously treated by Yukimaru Sugiyama, infanticide was attributed to stress causing factors like overcrowding and captivity, and was considered pathological and maladaptive. Classical ethology held that conspecifics (members of the same species) rarely killed each other. By the 1980s it had gained much greater acceptance. Possible reasons it was not treated as a prevalent natural phenomenon include its abhorrence to people, the popular group and species selectionist notions of the time (the idea that individuals behave for the good of the group or species; compare with gene-centered view of evolution), and the fact that it is very difficult to observe in the field.

In humans, family structure is the most important risk factor in child abuse and infanticide. Children who live with both their natural (biological) parents are at low risk for abuse. The risk increases when children live with step-parents or with a single parent. Children living without either parent (foster children) are 10 times more likely to be abused than children that live with both biological parents.

Children who live with a single parent that has a live-in partner are at the highest risk: they are 20 times more likely to be victims of child abuse than children living with both biological parents.

Infanticide is a subject that some humans may find discomforting. Cornell University ethologist Glenn Hausfater states that "infanticide has not received much study because it's a repulsive subject. Many people regard it as reprehensible to even think about it." Research into infanticide in animals is in part motivated by the desire to understand human behaviors, such as child abuse. Hausfater explains that researchers are "trying to see if there's any connection between animal infanticide and child abuse, neglect and killing by humans. We just don't know yet what the connections are."

Infanticide has been, and still is, practiced by some human cultures, groups, or individuals. In many past societies, certain forms of infanticide were considered permissible, whereas in most modern societies the practice is considered immoral and criminal. It still takes place in the Western world usually because of the parent's mental illness or violent behavior, as well as encompassing the reasons for elective abortion, in addition to some poor countries as a form of population control — sometimes with tacit societal acceptance. Female infanticide, a form of sex-selective infanticide, is more common than the killing of male offspring, especially in cultures where male children are more desirable.