11 Mar 09 SEX DIFFERENCES – PSIHOLOGY 3
What can be concluded from these important studies? Only that pre-natal hormones may have a small effect on behaviour after birth, at least in choice of toys and in tomboyish activity, and that the hormones may alter the person’s threshold to certain activities.
This possible influence can be examined in another way. A small number of male foetuses have a genetic defect which renders the tissues of their body insensitive to the testosterone secreted by their testes, although the other substance which inhibits the growth of the female ducts is secreted and is effective. These children are born with female external genitals and a very short vagina (but no internal genitals). They look exactly like baby girls and are brought up as girls. At puberty, their breasts develop like those of other girls, but they fail to grow body hair and they fail to menstruate. This leads to an investigation when the true situation is disclosed. Although these children are genetically male, all their behaviour in childhood, their sexual hopes, their dreams, and their fantasies are feminine and the children tend to be non-aggressive. While this could be entirely due to childhood conditioning, as the children are considered to be girls by their parents from birth, it is possible that their lack of sensitivity to testosterone has prevented the ‘male’ imprint on their brain cells occurring. Dr Money suggests that these findings are evidence that in humans, as in other mammals, the sex hormones imprint a pattern on the foetal brain. But it seems, as I mentioned in the last chapter, that the effect of pre-natal testosterone is to ‘blur’ or ‘flavour’ the behaviour of the child, rather than modify it markedly.
This theory would be strengthened if it could be shown that male and female foetuses have different levels of testosterone circulating in their tiny bodies. And they have! If the foetus is male, it makes a larger quantity of testosterone than if it is female, particularly between the 10th and 30th weeks of pregnancy. This could presumably give the ‘blurring’ to the behaviour of the child after birth, although there are two problems.
The first is that, although more testosterone is made by male foetuses, there is an overlap; some female foetuses produce as much testosterone as do males. The second is that from the 30th week of pregnancy there is very little difference in the amount of testosterone produced by either sex. This may be important as the brain cells grow more quickly and make most of their connections with their neighbouring brain cells, to complete circuits, after the 30th week of pregnancy.
The effect of testosterone during the time the boy is in his mother’s uterus may also condition or permit boys to learn aggressive behaviour earlier and more easily than girls. In boys, aggressive tendencies begin at about the age of 5. Small boys indulge in more rough-and-tumble play, push other children more, and hit them more than little girls do. Small boys imitate aggressive acts more often than girls after seeing aggression on television or at a film. More small boys choose television programmes in which there is more aggression, than do girls. Small boys, who form groups more frequently than girls, are more hostile to a newcomer seeking to break into the group. Small boys are verbally more aggressive and have more aggressive fantasies when day-dreaming, than do girls. But once again there is a problem in accepting that the behaviour is due to testosterone rather than to the ways boys are reared.
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