Nature or Nurture? Why Soldiers Get A Kick Out Of Killing, By John Horgan

Do some soldiers enjoy killing? If so, why? This question is thrust upon us by the recently released video of U.S. Apache helicopter pilots shooting a Reuters cameraman and his driver in Baghdad in 2007. Mistaking the camera of the Reuters reporter for a weapon, the pilots machine-gunned the reporter and driver and other nearby people.

The most chilling aspect of the video, which was made public by Wikileaks, is the chatter between two pilots, whose names have not been released. As Elizabeth Bumiller of The New York Times put it, the soldiers "revel in their kill." "Look at those dead bastards," one pilot says. "Nice," the other replies.

The exchange reminds me of a Times story from March 2003, during the U.S. invasion of Baghdad. The reporter quotes Sgt. Eric Schrumpf, a Marine sharpshooter, saying, "We had a great day. We killed a lot of people." Noting that his troop killed an Iraqi woman standing near a militant, Schrumpf adds, "I'm sorry, but the chick was in the way."

Does the apparent satisfaction—call it the Schrumpf effect—that some soldiers take in killing stem primarily from nature or nurture? Nature, claims Richard Wrangham, an anthropologist at Harvard University and an authority on chimpanzees. Wrangham asserts that natural selection embedded in both male humans and chimpanzees—our closest genetic relatives—an innate propensity for "intergroup coalitionary killing" [pdf], in which members of one group attack members of a rival group. Male humans "enjoy the opportunity" to kill others, Wrangham says, especially if they run little risk of being killed themselves.

Several years ago, geneticists at Victoria University in New Zealand linked violent male aggression to a variant of a gene that encodes for the enzyme monoamine oxidase A, which regulates the function of neurotransmitters such as dopamine and serotonin. According to the researchers, the so-called "warrior gene" is carried by 56 percent of Maori men, who are renowned for being "fearless warriors," and only 34 percent of Caucasian males.

But studies of World War II veterans suggest that very few men are innately bellicose. The psychiatrists Roy Swank and Walter Marchand found that 98 percent of soldiers who endured 60 days of continuous combat suffered psychiatric symptoms, either temporary or permanent. The two out of 100 soldiers who seemed unscathed by prolonged combat displayed "aggressive psychopathic personalities," the psychiatrists reported. In other words, combat didn't drive these men crazy because they were crazy to begin with.

Surveys of WWII infantrymen carried out by U.S. Army Brig. Gen. S.L.A. Marshall found that only 15 to 20 percent had fired their weapons in combat, even when ordered to do so. Marshall concluded that most soldiers avoid firing at the enemy because they fear killing as well as being killed. "The average and healthy individual," Marshall contended in his postwar book Men Against Fire, "has such an inner and usually unrealized resistance towards killing a fellow man that he will not of his own volition take life if it is possible to turn away from that responsibility…At the vital point he becomes a conscientious objector."

Critics have challenged Marshall's claims, but the U.S. military took them so seriously that it revamped its training to boost firing rates in subsequent wars, according to Dave Grossman, a former U.S. Army Lieutenant Colonel and professor of psychology at West Point. In his 1995 book On Killing, Grossman argues that Marshall's results have been corroborated by reports from World War I, the American Civil War, the Napoleonic wars and other conflicts. "The singular lack of enthusiasm for killing one's fellow man has existed throughout military history," Grossman asserts.

The reluctance of ordinary men to kill can be overcome by intensified training, direct commands from officers, long-range weapons and propaganda that glorifies the soldier's cause and dehumanizes the enemy. "With the proper conditioning and the proper circumstances, it appears that almost anyone can and will kill," Grossman writes. Many soldiers who kill enemies in battle are initially exhilarated, Grossman says, but later they often feel profound revulsion and remorse, which may transmute into post-traumatic stress disorder and other ailments. Indeed, Grossman believes that the troubles experienced by many combat veterans are evidence of a "powerful, innate human resistance toward killing one's own species."

In other words, the Schrumpf effect is usually a product less of nature than of nurture—although "nurture" is an odd term for training that turns ordinary young men into enthusiastic killers.

ABOUT THE AUTHOR

John Horgan, a former Scientific American staff writer, directs the Center for Science Writings at Stevens Institute of Technology. (Photo courtesy of Skye Horgan.)