The most basic information is this: if you are a genetic female, you are a XX sex chromosome. If you are a genetic male: you are a XY sex chromosome. Males determine the sex of a child as they have both an X and a Y. Females can only contribute X’s. There is a gene on the Y chromosome that is called the TDF or testis determining factor that causes male fetuses to grow testicles. The testicles produce testosterone which cause male attributes. Anything that disrupts either the testicles or blocks the hormones creates a child that looks female. There are other chromosome combinations such as XXX, XYY< XYYY and XO. There were studies done a few decades ago showing disproportionate numbers of XYY and XYYY men in prison. And XO females are exceptionally docile individuals. These docile females have Turner’s syndrome and are ultra female. They are sterile. If something goes wrong with the development of testicle’s, the female appearing or feminine male individual has Klinefelter’s syndrome.

Up until the child grows testicles and produces his own hormone, he is at the mercy of his mother’s hormones which are female. This means we all start off as female, until that time the brain and body are happily becoming female. At this point when the male hormones start to work the brain suddenly begins to become male. It is presently thought that this is when males develop their larger numbers in disorders of the brain such as autism. Testosterone levels in the two month old fetus is as high as it is in the adolescent male. Once the brain is programed to receive either male or female hormones, it can never be reprogrammed.

In his book, The Sexual Brain, Dr. Simon LeVay talks about the feminisation of rat pups which are born at what would be only a few weeks gestation in a human. By giving female hormones to the pups on different days, they saw different behaviors being affected. You could have a male rat that was normal except he wanted to care for the pups and so forth. Of course there are no such tests on humans, but this would go a long way towards explaining our broad sexual tendencies.

There has been a long nature versus nurture debate running. There are good arguments for both sides. That children are born a blank slate has been largely debunked, however, as we are beginning to see that children are born with strong male or female tendencies.