Lewis Wolpert: 'It makes sense males should care more about technology'

The basic human body is female. Males are essentially hormonally modified females, a process that takes place in both the embryo and after birth.

The basic human body is female. Males are essentially hormonally modified females, a process that takes place in both the embryo and after birth.

This sex change is initially determined by the genes on a Y chromosome brought in by a male sperm. Genes on the Y lead to the embryo developing a testis and this in turn results in male hormones, androgens, being made, and it is these hormones that control male sexual differences, such as the development of male sexual organs. Males also have bigger brains, and there are additional subtle differences between the brains of the two sexes. But genetic sex is not the same as gender, that is whether the individual and others see themselves as male or female. Moreover, gender may not correspond with genetic sex - things can go wrong. Boys and girls are clearly different in their behaviour. What causes these differences? Does it lie in the hormones or are social interactions the key cause? Some answers are to be found in Melissa Hines' recent book Brain Gender (Oxford University Press USA).

Behavioural differences can be seen early in life and by 12 months boys and girls prefer different toys. Boys tend to choose toys with mechanical associations such as trucks and guns, while girls prefer dolls and tea-sets. Boys prefer rough and tumble games, including fighting. Studies on male children have shown that those who become homosexual as adults were found to have a significantly greater than normal preference for girls' toys.

There is good evidence for hormones playing a key role in determining this behaviour, both when the embryo was in the womb and in later life. If a girl is exposed in the womb to high levels of the male hormones - androgens - their later behaviour is much more like that of a male child. Early studies were viewed with some scepticism, but a number of recent studies have been very persuasive. But this may not be due to the action of the hormones directly affecting male and female behaviour, but rather could reflect their sense of identity, as both boys and girls mainly prefer playmates of their own sex, and tend to imitate the behaviour of children of the same sex. Girls who had been exposed to high androgen levels often identify more with boys than girls.

Both learning and the behaviour of adults could also play a key role in the sex differences found in play. Parents typically encourage what they believe to be the appropriate behaviour for their children. Negative reactions have been observed when, for example, boys play with dolls. Again, careful studies show that boys are encouraged to play with blocks and girls with feminine toys. When asked to interact with an infant dressed so the sex is not obvious, strangers will offer masculine toys if told the child is a boy, and vice versa. They also, when viewing a video, label the same emotional response in a child as anger if told it is a boy, and fear if they think it is a girl.

The male preference for trucks and balls may reflect that they offer the possibility of more active play, and this is in line with the evidence that boys are more active even while in the womb, and that this continues through childhood. It is striking that some animals show similar patterns of behaviour to human children with respect to what they like to play with.

Melissa Hines gave vervet monkeys access to children's toys. Just like children, the females spent more time with the doll and the cooking pot, while the male monkeys preferred the car and ball. This implies that these differences are genetically determined in the brain and have been selected because they are advantageous in evolution.

There is also evidence that there are some differences in brain function between males and females. This is not related to intelligence, but to male abilities to mentally rotate moderately complex geometric objects.

This could help males with technology. It makes evolutionary sense that males should care more about technology, and females about the family, to put it crudely, but probably correctly.

Lewis Wolpert is Professor of Biology as Applied to Medicine, at University College, London