The extreme man
Men vary more than women do in size as well as in physical and mental performance.
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This trend continues from cradle to grave.
Researchers have analysed the birth weight of all the babies born in a single year in Norway – nearly 48,000 infants.
“Variations in weight among newborns were greatest among boys,” says one of the researchers, Anne-Catherine Lehre. She recently presented her doctoral thesis at the Institute for Basic Medical Sciences at the University of Oslo.
She and her colleagues also conducted a study that included information about heights and weights of more than 2,700 adults in the Nordic countries, where variations were also wider among men.
“Greater variation in mental as well as physical traits among males could be a fundamental difference between the sexes,” says Lehre.
Sampling 30 different substances
Blood tests of all the test persons were taken in the same study. Researchers focused on 30 common body substances such as levels of glucose, cholesterol, sodium and magnesium.
Here too the values were more widely spread among men than women.
“This surprised us because the samples from women were taken during different times in their menstrual cycles, so we expected this to raise the variation among them,” says Lehre.
The wider variation in the blood values among the men could be attributed to their larger range of body sizes.
In physical performance, such as running 60-metre dashes in junior high school, results among boys are more differentiated than among girls.
Unexpected outcome in higher education
The greater variations among men also included mental achievements such as exams in higher education, which were surprising.
Lehre and the other researchers in the project analysed upwards of 5 million exam results from upper levels of education from 1990 to 2007 to find variations in mental performance among men and women.
They also checked whether the results varied after reforms in higher education were implemented in the summer of 2003.
At the Bachelor’s Degree level the average grades of women and men were nearly the same, but the range of grades among men was higher. Men had the best and the worst grades.
“At the Masters level men had better grades than women on average, but following the reform women had better grades in the lower and upper degrees,” says Lehre.
Women were winners in the educational reform
Prior to 2003 grades were usually based solely on the results of a final exam. After the reform marks were additionally based on results in an intermediate exam or papers submitted during courses.
Previous studies have shown that the same type of changes made in teaching in connection with the reform improved results among students who had average grades.
“Women were closer to the average in the grading scale than men. So this could explain why more women benefited from the changes,” says Lehre.
Women varied more in BMI
The only factor where women had a greater variation than men was in the body mass index BMI, which is based on height and weight.
Women’s scores are more varied than men’s and they have a higher average BMI than men.
Is the X-chromosome the X factor?
Lehre suggests that the fact that men exhibit more differentiation than women in so many ways could be that women have two X-chromosomes, whereas men only have one.
This means that variations in a man’s X-chromosome can have a bigger impact than it would in one of women’s two.
Half of a woman’s cells are expressed by one of her X-chromosomes, and in these cells the other X-chromosome is deactivated. In the other half of her cells the second X-chromosome is the key and the first one is deactivated.
This means that a woman is expressed as the average of her two X-chromosome. Female genes will have less variation than male genes according to Lehre.
Planning a study of gender differences in school
The researchers studied data using statistical analysis methods. The results have so far been published in two scientific articles.
Now Lehre wants to study the results in girls and boys all the way from primary school to university levels to see how different forms of teaching and other factors affect learning and mental performance among the sexes.
Read this article in Norwegian at forskning.no
Translated by: Glenn Ostling