According to the Families and Work Institute in New York,　fathers provide nearly three-fourths of the childcare responsibilities that mothers perform, up from one-half　30 years ago. But are fathers　really up to the task? Men are often deemed too competitive and too driven to make good parent-nurturers. Many people, including even social scientists, describe domineering, competitive male attributes to male hormones, especially testosterone. The media actively supports this image. One article in Reader's Digest, for example, entitled “Why Men Act as They Do,” is subtitled, “lt's the Testosterone, Stupid!” The article argues that testosterone is “a metaphor for masculinity” and concludes that “testosterone correlates with risk-physical, criminal, personal.” With such images, men appear destined to be anything but nurturing parents.     Two new studies from Canadian universities provide a very  different perspective. The research shows that testosterone plays a role in mating and conception, but that other hormones play a more role in transforming men into nurturing fathers. The first important  study, conducted by Anne Story, found that three hormonal changes took place in both mothers and fathers during pregnancy and after birth. The hormone prolactin promotes lactation in women and increases parental bonding. Cortisol is a stress hormone that heightens alertness and boosts sympathetic relationships between mothers and their infants. 　　The two hormones were known to play roles in the development of positive mothering, but the important research showed that three weeks before birth the prolactin levels of expecting fathers increased by 20 percent, and their cortisol level shot  up to twice the normal level. Their testosterone levels were observed to fall by 33 percent during the first three weeks after delivery, though the level returned to normal several weeks later. Researchers believe that even this ephemeral dip in testosterone may open a window of opportunity for the father to bond more fully with the infant, a bonding that lasts beyond the infant’s early years.     Later research by Wynne Edwards found that fathers also showed increases in the female hormone estrogen 30 days prior to birth, and that the increased level continued throughout the period of        which terminated 12 weeks after delivery. Animal studies have shown that estrogen induces nurturing behavior in males.   Researchers believe that intimate contact between the partners spurs the changes m men. All of the fathers in the study were living with their female partners. “My guess is that women's hormone levels are Limed to the birth,” Story says, “and that men's hormone levels are tied to their partners'.” However, no one knows exactly how the changes m men occur. The researchers speculate that female partners communicate with male partners through chemical messages, such as pheromones that animals give off through their skin. Until recently, it was assumed that fathers only became bended to their children through prolonged exposure, and that this bonding was uncertain and tentative-certainly not biological. It now seems likely that men are biologically designed to play a role in child rearing, and that their hormonal shifts may shape them into devoted dads.