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. […]
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.”
Scientific American Guest Blog: Why soldiers get a kick out of killing
(via Wikileaks)