Being a man has always been dangerous. There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year- olds there are twice as many women as men.But the great universal of male mortality is being changeD、Now, boy babies survive almost as well as girls do. This means that, for the first time, there will be an excess of boys in those crucial years when they are searching for a mate. More important, another chance for natural selection has been removeD、Fifty years ago, the chance of a baby (particularly a boy baby) surviving depended on its weight.