Biological theories of war have inspired a slew of bio-solutions, which aim to repress, vent, or redirect our allegedly innate urge to fight. One of the most radical was proposed in the late 1960s by the Yale neurophysiologist Jose Delgado. Delgado, ironically, was one of the original signers of the Seville Statement, which repudiates biological theories of war. But he suggested that war and other forms of violence could be curbed by implanting radio-controlled electrodes in peoples' brains.

Delgado was the pioneer -- and flamboyant promoter - of this technology. In 1963, he stood in a Spanish bullring as a bull with a radio-equipped array of electrodes implanted in its brain charged toward him. Delgado pushed a button on a radio transmitter, causing the "stimoceiver" to zap a region in the bull's brain supposedly associated with aggression. The bull stopped in its tracks and trotted away. The media marveled at Delgado's transformation of an aggressive beast into a real-life version of Ferdinand the Bull, the gentle hero of the popular children's story.

In other experiments, Delgado manipulated the limbs and emotions of cats, monkeys, chimpanzees, and humans (most of them mental patients) with implanted electrodes. In 1969, he extolled the potential benefits of brain-stimulation technologies, which would help us create "a less cruel, happier, and better man." In the 1970s, brain-implant research got bogged down in technical and ethical issues, but it has recently made a comeback, as scientists have begun exploring the potential of implanted devices for treating epilepsy, depression, paralysis, and other disorders of the nervous system. The Pentagon has become a major funder of research on brain-implant devices, which could in principle boost soldiers' physical and mental powers -- and make them easier for commanders to control. This technology raises an obvious question: Who gets the brain implant, and who gets the remote controller?

In the heyday of eugenics in the late nineteenth and early twentieth centuries, some scientists and commentators proposed that we reduce our aggression through selective breeding, just as breeders of dogs, cats, cattle, and other domestic animals have done. The Nazis gave eugenics a bad name, but recent research on genes associated with inherited diseases has resuscitated the idea that we can engineer ourselves to be nicer. Another possibility, say some, is pacifying people with drugs called serenics. One possible candidate is the hormone oxytocin, which has been linked to primates' feelings of affection and trust.

Other bio-solutions are cultural rather than strictly physiological. In his 1906 essay "The Moral Equivalent of War," William James suggests channeling young men's martial urges into a "war against nature," which would entail fishing, logging, digging tunnels, and other risky, invigorating work. The biologist and Nobel laureate Konrad Lorenz, in his 1963 book On Aggression, proposes that societies vent their aggression through "sporting contests" both within and between nations. Some scholars have taken this proposal seriously enough to test it, and they have found no correlation between societies' propensity for war and their fondness for sports.