In fact, as researchers are discovering, the psychology of risk involves far more than a simple "death wish." Studies now indicate that the inclination to take high risks may be hard-wired into the brain, intimately linked to arousal and pleasure mechanisms, and may offer such a thrill that it functions like an addiction. The tendency probably affects one in five people, mostly young males, and declines with age. It may ensure our survival, even spur our evolution as individuals and as a species. Risk taking probably bestowed a crucial evolutionary advantage, inciting the fighting and foraging of the hunter-gatherer.