Evidence is piling up (like those packages under the tree) that human beings were born to give. Their very physiology makes them do it. Studies show that when a person gives money to a stranger or a charity, the "rewards area" of the brain gets busy. It's the same area that goes to town when the person eats a sugar cookie or finds a parking place at the mall or receives a gift of money from Ed McMahon.

Not only that, but generous people also seem to live longer and stay healthier than those "bah humbug" types, according to population studies. It's even possible (scientists are busy testing this concept now) that the more Christmas spirit shoppers have, the fewer bugs they're likely to catch during the holidays.

Gift-giving, in a nutshell, seems to improve people's health and longevity. It lifts their mood and bolsters their ego. And perhaps most important of all, it makes people beholden to one another, so that when their goose is cooked, they have friends to save their skin. Or so goes the evolutionary theory.

"The most important thing I learned in writing a whole book about human relationships is 'give more gifts,' " says evolutionary biologist Jay Phelan, a life sciences academic administrator at UCLA and co-author of "Mean Genes: From Sex to Money to Food: Taming Our Primal Instincts." A gift doesn't have to be expensive, studies show. It really is the thought that counts -- well, the thought and the pretty wrapping.