Kirk Vanacore1: Evolution and Infanticide

Kirk Vanacore

Evolution and Infanticide

 

Evolution is link directly to reproductive success. If a trait enhances one’s chances of reproducing, the trait is more likely to become prominent. One question rises: are we mentally prone to act in this way? Michael S. Gazzaniga is certain this is so: “To be sure, the human brain is a bizarre device, set in place through natural selection for one main purpose – to make decisions that enhance reproductive success.”[1] A prominent biologist, Edward O. Wilson, agrees: “The human mind is a device for survival and reproduction.”[2] But it seems rather narrow minded to reduce all of humanities actions to these two ends. After all it seems that humans don’t spend most of their time gathering essential resources and having sex. There is also one major contradiction Gazzaniga brings up himself: infanticide. Many animals, including our closest relatives the primates, will kill babies – sometimes with the purpose of simply mating again with the mother. So, if the human brain’s goal were reproduction, why would one kill the products of reproduction – infants?

 

Gazzaniga states “infanticide is a typical behavior in many species within every group of animals – birds, fish, insects, rodents, and primates.”[3] The reason, he explains is economic:

What makes it possible for these species to kill, just as it is possible for some to indulge in infanticide, is once again economic. It is cheap to kill. The cost-to-benefit ration is good. When you kill and infant, you don’t really risk being injured yourself, so the cost is low. You gain either a food source or increased change of mating with the female because when her infant is dead, she will stop lactating and ovulate again.[4]

Infanticide is done because it will benefit the killer; the animal will gain something whether it is simply more food or a chance to reproduce. Studies have even shown that infanticide is an evolutionary adaptation meant to increase the killer’s chance in mating. One German study of langur monkeys showed that the monkeys who committed infanticide, often mated with the mothers of the dead infants.[5]

While this may explain part of the brain’s instinct toward infanticide, there is another side to the tendency. A study by Doctor Susan Levitzky found that some human mothers had thoughts of infanticide. The children of the mothers had infant colic syndrome, a condition where the infant may scream perpetually for long periods of time due to stomach pain. The study revealed that 70% of the mothers considered aggressive actions against their children and 26% considered infanticide.[6] This raises a major question about the human brain: if the brain’s two main goals are survival and reproduction, why would mothers consider killing their offspring when they do not threaten their mother’s survival? This case suggests that are other considerations, like comfort or peace, that may even trump reproduction when the human brain makes decisions.

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[1] Gazzaniga; “Human: The Science Behind What Makes Us Unique;”  Harper Collins, New York (2008), p29.

[2] Wilson; “On Human Nature;” Harvard University Press (1978).

[3] “Human” p68.

[4] “Human” p 72.

[5] Borries, Launhardt, Epplen, Epplen, Winkler; “DNA analyses support the hypothesis that infanticide is adaptive in langur monkeys,“ The Royal Society; Proc. R. Soc. London; B (1999) 266.

 

[6] Levitzky, MD; “Infant Colic Syndrome—Maternal Fantasies of Aggression and Infanticide” Clinical Pediatrics, Vol. 39, No. 7, 395-400 (2000).