If Robert Sapolsky wasn’t a bit of a comedian as well as a celebrated neuroscientist, he may have had his audience clenching their teeth rather than bursting into fits of laughter. For his presentation on the effects of stress on the human body and brain contained a powerful message: stress kills slowly, suppressing the immune system, shutting down growth, and eroding memory and the ability to learn.

Many of Sapolsky’s insights regarding the effects of stress first emerged during the years he spent studying primates in the Serengeti in Africa. "Stress is anything in the external world that knocks you out of homeostatic balance, "Sapolsky said. "Let’s say you’re a zebra, and a lion has leaped out, ripped your stomach out. . . this counts as being out of homeostatic balance."

For a zebra, though, stress had an extremely short if potentially deadly span; it was "three minutes of screaming terror" after which the animal was either dead or once again roaming the Savannah and feeling safe. Human beings, on the other hand, had an "anticipatory stress response" that spun easily out of control, like a car losing traction on an icy slope.

"If you think you’re about to be knocked out of homeostatic balance and really aren’t, and this happens on a regular basis, then you’re being anxious. . . paranoid. . . profoundly human," Saplosky said. The point is that humans, unlike primates, "can get stressed simply with thought, turning on the same stress response as does the zebra." And when that stress response is turned on chronically, "We get sick."