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Animals and humans sometimes kill their young -- the question is why

Horrendous attack on children in Pakistan causes a neuroscientist to examine why animals kill their young

Among the endless stream of bad news in the media, every now and then something occurs that it is so horrendous that it stops us in our tracks. That has happened once again with Tuesday's massacre at a school in Peshawar, Pakistan. Among the victims: 132 children who died — many of them shot at close range.

It would be appalling enough if this were the work of someone destroyed by mental illness of a particularly rare, ghastly sort. But it is even more astonishing because it was strategic, the work of a branch of the Taliban intent on destabilizing the government. An organization, a group that probably tries to balance its budget, has media spokesmen and recruits through Facebook. A group that purposely slaughtered children as it carried out one of the deadliest terrorist attacks in Pakistan's history.

The depravity of this act has moved me to share an anthropological story that could be lifted from a Grimms' fairy tale but happens to be true.

In the 1970s, a young Harvard University primatologist named Sarah Hrdy came back from doing fieldwork in India, where she studied Hanuman langurs, a species of monkey. She had observed something remarkable, and almost no one believed her.

She reported that male langurs would occasionally kill infants, and this ran counter to knowledge in the field, namely that humans are the only species that kills its own kind and that the young fall into a protected category. In almost every species, short of tarantulas, the young share characteristic features — big googly eyes, short snouts, round ears, higher foreheads and proportionately bigger heads.

To toss around some scientific jargon, young animals are “cute.” And research had shown that this adorableness helps elicit parental care. Be they polar bears, humans or field mice, the cuteness of kids prompts parents to desire to pay for piano lessons and a new pair of ice skates for them. The young also inherently inhibit aggression from their elders. Or so everyone thought.

As Hrdy documented this phenomenon, zoologists began to accept that langurs sometimes kill the young of other animals. But the admissions were waved away as abnormal behavior. Scientists would offer a semi-hypothetical explanation that reflected some sort of pathology — they'd say that perhaps the population density was too high and animals were starving, dismiss it as an overflow of generic male aggression or declare that infanticidal males were possibly zombies. Yet none of the theorizing explained the behavior.

Hrdy learned more, and soon other zoologists were reporting the same phenomenon in other species, including lions and gorillas. And the increasing number of pieces of the puzzle began to provide a plausible explanation.

In infanticidal species, there's a consistent social structure. Groups of (typically related) females live with a single breeding male who engages in that evolutionary business of passing on lots of copies of his genes. Meanwhile, other males grumble on their own in the hinterlands. Eventually, some peripheral male challenges the resident male, drives him out and becomes the new breeding male. But it won't be long until the same fate befalls the new male. In the meantime, many of the females aren't fertile because they're nursing infants. Realpolitik solution for the male? Kill the infants. It sets back the reproductive success of the previous male, the females stop nursing and start ovulating — and he succeeds in passing on his genes.

In other words, there's logic, carried out unconsciously in these species, underlying such “competitive infanticide.” For zoologists, the most important implication of these pioneering studies is that from the standpoint of evolution, it can be strategically advantageous to kill someone else's offspring. (In fairness, various species display an equivalently strategic logic that favors great displays of altruism toward someone else's offspring).

That brings us to varied occasions where humans go about killing someone else's child.

Two years ago, Adam Lanza entered Sandy Hook Elementary School in Newtown, Conn., and killed 20 children and six adults, before taking his own life. Lanza was a lone wolf with neurodevelopmental problems not of his own making. Someone who inconceivably had access to guns and was taken for target practice by his gun-enthusiast mother (whom he also killed). This was an act of deep pathology, as was the case with Seung-Hui Cho in 2007 at Virginia Tech, Elliot Rodger in May in Isla Vista, Calif., near UC Santa Barbara and so many other school shootings in recent history.

And then there are the slayings of the children in Peshawar. This was not the work of a Lanza, Cho or Rodger. This was a venture requiring teamwork. The killers probably held planning meetings to carry out the massacre, complete with PowerPoint presentations and Danish rolls. The group carried out this slaughter with depravedly rational ideological and theological motivations — rational in the sense of acting to gain power, in contrast to the irrational goal of, say, acting because their imaginary friend told them to.

Yes, we humans are often unexpectedly similar to other species. Sometimes we demonstrate that to an extent that could almost make a langur monkey weep along with us. 

Robert M. Sapolsky is a professor of neuroscience at Stanford University and the author of "A Primate's Memoir," among other books. He is a contributing writer to Opinion.

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