Male scientists typically have a level of the hormone oestrogen as high as their testosterone level

Oct 21 2004

A survey of academics at the University of Bath has found that male scientists typically have a level of the hormone oestrogen as high as their testosterone level.

These hormone levels are more usual in women than men, who normally have higher levels of testosterone.

The study draws on research which suggests that these unusual hormone levels in many male scientists cause the right side of their brains, which governs spatial and analytic skills, to develop strongly.

The study, which has been submitted to the British Journal of Psychology, also found that:

• these hormonal levels may make male scientists less likely to have children.
• those men with a higher level of oestrogen were more likely than average to have relatives with dyslexia, which may in part be caused by hormonal levels.
• women social scientists tended to have higher levels of testosterone, making their brains closer to those of males in general.

The study drew on work in the last few years which established that the levels of oestrogen and testosterone a person has can be seen in the relative length of their index (second) and ring (fourth) fingers. The ratio of the lengths is set before birth and remains the same throughout life.

The length of fingers is genetically linked to the sex hormones, and a person with an index finger shorter than the ring finger will have had more testosterone while in the womb, and a person with an index finger longer than the ring finger will have had more oestrogen. The difference in the lengths can be small – as little as two or three per cent – but important.

A survey of the finger lengths of over 100 male and female academics at the University by senior Psychology lecturer Dr Mark Brosnan has found that those men teaching hard science like mathematics and physics tend to have index fingers as long as their ring fingers, a marker for unusually high oestrogen levels for males.

It also found the reverse: those male academics with longer ring fingers than index fingers – the usual male pattern – tended not to be in science but in social science subjects such as psychology and education.

A further study also suggests that prenatal hormone exposure, and hence index finger length, can also influence actual achievement levels. In a survey of male and female students on a JAVA programming course at the University, the researchers found a link between finger length ratio and test score. The smaller the difference between index and ring finger - the higher the test score at the end of the year.

“The results are a fascinating insight into how testosterone and oestrogen levels in the womb can affect people’s choice of career and how these levels can show up in the length of fingers on our hands,” said Dr Brosnan.

“In the general population, men typically have higher levels of testosterone than women, but the male scientists at the University of Bath have lower testosterone levels than is usual for men – their oestrogen and testosterone levels tend to match those of women generally.

“This research now suggests that lower than average testosterone levels in men lead to spatial skills that can give a man the ability to succeed in science. Other research has in the past also suggested that an unusually high level of testosterone can do the same thing by encouraging the development of the right hemisphere.

"This right brain development is at the expense of language abilities and people skills that men with a more usual level of testosterone develop and which can help them in social science subjects like psychology or education.”

Dr Brosnan said that men having levels of testosterone very much higher than normal for males would also create the right hemisphere dominated brain which could help in science. The extremes of low testosterone and high testosterone for men would create the scientific brain, and the normal range in the middle would create the ‘social science’ brain, he said.

“The question also arises as to why more women, who have this lower level of testosterone, are not in science, which is male-dominated, with only one in 40 science professors being a woman.

“The short answer is that we don’t know: the high levels of oestrogen in women may act differently on the brain and not give them the spatial skills that men with similar levels of the hormone have.

“Or their may be social reasons: science has been male-dominated the past and this may be putting women off entering it, even though they are able to.

“Why male scientists should have fewer children is not known.

“The study of my colleagues at the University of Bath was also interesting in that it shows that women in social science tend to have a higher level of testosterone level relative to their oestrogen level, making their brains closer to those of men in general.”