Are women really hard-wired to be more sociable than men? Not long ago, many feminists believed that the differences between men and women were due to the way boys and girls are raised, especially in early childhood. Recent studies, however, suggest that it may be "nature over nurture," at least where friendship is concerned.

Boys and girls are often raised differently, but it's beginning to appear that females possess social skills from birth. Studies on day-old babies show that girls stare longer at human faces than mechanical objects, while boys do just the opposite. Cambridge University psychologist Simon Baron-Cohen, who performed many of these studies, writes about them in The Essential Difference: The Truth About the Male and Female Brain (Basic Books, 2003). "On average," he says, "women engage in more consistent social smiling and maintained eye contact than does the average man."

Researchers tracking baboons in Kenya recorded the amount of time each female spent socializing -- sitting near and grooming each other. The females with the most elaborate social networks had the best chance of their offspring surviving. Susan Alberts of Duke University, one of the researchers on the Kenya study, suspects that the friendly females were less vulnerable to predators and healthier because of all the grooming they received.

Chris Schetter, a UCLA psychologist, has documented a similar pattern among human mothers. In 2000, she interviewed 247 pregnant women and found that those who got the most support from family and friends delivered higher-weight babies.

UCLA psychologist Shelley E. Taylor suggests that women respond to stress differently than men. In her book, The Tending Instinct (Times Books, 2002), Taylor theorizes that while men exhibit the well-known "fight or flight" response to stress, women turn to one another. She says that over time, women who formed strong bonds with other women were more likely to survive, as were their offspring. "Female ties have evolved to ensure that certain vital functions important to life get maintained," says Taylor, whose research started with an "aha!" moment at work. Taylor and her colleague at UCLA, Laura Klein, noticed that when women workers in their lab were stressed, they cleaned the lab and had coffee together. Their male co-workers, under the same pressures, holed up somewhere alone. When both scientists found that 90% of stress research was done on men, they realized they were on to something.

Taylor calls the female stress response "tend and befriend," and believes there may be a biological reason for it. The hormone oxytocin, which is released into a woman's bloodstream after childbirth, facilitates mother-infant bonding. Oxytocin is also released during stress and is enhanced by estrogen. When women actually engage in nurturing and socializing, more oxytocin is released, producing a calming effect. Testosterone, which men produce at high levels when under stress, tends to reduce the effects of oxytocin.

Another type of hormone, endogenous opioids, are also associated with feelings of relaxation and nurturing, and are released along with oxytocin when a woman nurses her baby. Scientist Larry Jamner of the University of California, Irvine, gave opioid blockers to 22 men and 29 women. The men were unaffected, but the women spent more time alone, called their friends less often and said that when they did socialize, it was less pleasant than usual.

Journalists Ellen Goodman and Patricia O'Brien documented their 25-year friendship in the book, I Know Just What You Mean: The Power of Friendship in Womens Lives (Simon & Schuster, 2000). They have worked hard over the years to maintain their strong connection, in the face of many changes. They lament the fact that in our stress-filled lives, many women feel they have to give up time with friends in order to keep up with job and family pressures. "Women can't help but see friendships as the 'treat' they can allow themselves only after the business of the day is done -- if it's done," write Goodman and O'Brien.

Ruthellen Josselson, coauthor of Best Friends: The Pleasures and Perils of Girls' and Women's Friendships (Crown, 1998), says "that's really a mistake, because women are such a source of strength to each other. We nurture one another." "There's no doubt," says Dr. Laura Klein of Penn State University and Taylor's co-researcher, "that friends are helping us live longer." The famous Harvard Nurses' Health Study found that the more friends women had, the less likely they were to develop physical impairments as they aged. Researchers concluded that not having close friends was as detrimental as smoking or being overweight.

Social ties lower blood pressure, heart rate and cholesterol. One study found that people with no friends were more likely to die over a 6-month period. Another study showed that those with the most friends cut their risk of death by more than 60%.

Whether we are sixteen or sixty, we protect our own health when we "tend and befriend." If we stay healthy, our families also benefit. Since many of us are caregivers, it's nice to know that science proves "tending" is good for us. We just need to make time to also receive that nurturing from others.