In their isolation native Sardinians became genetic incubators, amplifying certain traits over generations. Even today roughly 80 percent of them are directly related to the first Sardinians, says Paolo Francalacci of the University of Sassari. Somewhere in this genetic mix, he says, may lie a combination that favors longevity.

Tonino's family's diet is another factor. It's loaded with homegrown fruits and vegetables such as zucchini, eggplant, tomatoes, and fava beans that may reduce the risk of heart disease and colon cancer. Also on the table: dairy products such as milk from grass-fed sheep and pecorino cheese, which, like fish, contribute protein and omega-3 fatty acids. Tonino still makes wine from his small vineyard of Cannonau grapes, which in this mountainous part of Sardinia contain two to three times as much of a component found in other wines that may prevent cardiovascular disease.

But with globalization and modernization, even remote Sardinia is changing. Cars and trucks have eliminated the need to walk long distances. Young people are more outward-looking and less traditional. Obesity, virtually nonexistent before 1940, now afflicts about 10 percent of Sardinians. "Children want potato chips and pizzas. That's what they see on TV," says Tonino. "Bread and pecorino are old-fashioned."

One thing that hasn't changed: the Sardinians' dedication to family, which assures both support in times of crisis and life-extending care for the elderly. "I would never put my father in a retirement home," says Tonino's daughter Irene. "It would dishonor the family."

For Tonino, the workday still includes a late afternoon trek to pasture his 200 sheep. Looking jaunty in his cap, coat, and leather gaiters, he strides through a narrow opening in a stone wall, counting his sheep as they follow him. When three sheep try to squeeze through, they knock over a section of the wall. With disquieting ease, Tonino hoists the heavy rocks back into place. Then he leans back on a rock outcropping and assumes the age-old role of sentinel, a routine he has performed for many decades.

"Do you ever get bored?" I ask. Before the words leave my mouth, I realize I've uttered a heresy. Tonino swings around, pointing at me, dried blood still rimming his fingernail, and booms: "I've loved living here every day of my life."