The fact that some people pay doctors to slant the probabilities toward one sex or the other means they believe this still. People have always invented ways of predicting sex and loading the dice. If a couple wants a boy, the woman must lie on her right side during intercourse. Such recipes have regularly been given out and, since couples have about a 50 percent chance of getting what they want, all these prescriptions work some of the time. Sure, there are biological differences between girls and boys.
Boys are bigger, more muscular, more active, stronger, more competitive, tougher.
Girls are daintier, more accommodating, better listeners, more interested in other people. And so on. But how active children are will determine how muscular and strong they will be. Scientists have shown that, for all non-reproductive characteristics, the overlaps between boys and girls tend to be greater than the differences between them. Scientists also tell us that differences in the ways we socialize girls and boys are far greater than most people realize.