Fluid movement

Fluid movement

How men and women are less different than you think

The making of the sexes

Dec 29th 2010 | from PRINT EDITION

 

 

 

Man & Woman: An Inside Story. By Donald Pfaff. Oxford University Press USA; 232 pages; $27.95 and £15.99. Buy from Amazon.com, Amazon.co.uk

 

THE trouble with books about the differences between men and women is that the authors are all too often partisan, or perceived to be. Any writer brave enough to take on this subject needs to be meticulous and unflaggingly sceptical in his or her approach. Rebecca Jordan-Young, a sociomedical scientist at Barnard College, pulled this off last year with “Brain Storm” (Harvard), in which she showed up the flaws in research that attributes sex differences in behaviour to prenatal exposure to hormones.

Out of the rubble of the edifice she destroyed, or at least left wobbling dangerously, Donald Pfaff has constructed a far more complex structure, that more closely resembles what scientists know about this subject.

 

Mr Pfaff is the right man for the job. A neurobiologist at New York’s Rockefeller University, he has worked in the field for nearly half a century, focusing on how hormones affect the brain. Mr Pfaff’s lab was the first to demonstrate how a female hormone, oestrogen, acts on a rat’s brain to produce female mating behaviour, so he might be expected to defend his patch against attacks from the likes of Ms Jordan-Young. Instead he weaves a story of genetic, hormonal and environmental influences that interact in myriad and complex ways to determine gender. He also resists the temptation to draw too many parallels between rats and humans. Though it is a reasonable assumption that these species share the brain mechanisms that control basic sex behaviours—erection, ejaculation and so on—in humans the biological is also powerfully modulated by social and cultural influences.

 

The story of sex determination starts with DNA, since your genes launch you onto a male or female trajectory. But as Mr Pfaff explains, if for any reason your hormones fail to follow suit, you can grow up assuming the other gender. Even if your genes and hormones are in synch, environmental factors can reroute the gender train. Under stressful conditions, for example, a pregnant woman’s adrenal glands pump out abnormal levels of another female hormone, progesterone, feminising the developing brain of a male fetus.

 

What’s more, the process of sex determination is not over by birth, but continues into life, up to and including puberty. And, when it comes to humans and sex, variety is infinite. Strongly masculine and strongly feminine genders mark each end of the spectrum. In between, every permutation is possible, and the same goes for sexual orientation.

 

In some ways men and women are consistently different, but the significant differences in their brains only pertain to those primitive behaviours which include mating, parenting and aggression. When it comes to higher functions—the skills that arguably make us human—the similarities outweigh the differences. on average, men and women score equally on mathematical and reading ability, for example. Reported differences in empathy, leadership and verbal fluency have all been exaggerated, according to Mr Pfaff. Where differences in these skills do exist, the causes may lie in the social context. The rise of the high-achieving “alpha girl” is in part due to social changes that have allowed girls equal access to education. The reasons why many boys perform poorly at school are complex, but partly social too.

 

Mr Pfaff is both meticulous and sceptical, but he has a tendency to be too technical for the general reader. And although he is convincing about the existence of a gender continuum, society still frets over what to do about children whose behaviour falls in the middle, or who, more unusually, are born with ambiguous genitals. Controversy still rages over the best way to treat this last group, and medicine can claim both successes and failures. Mr Pfaff’s book is the latest of many works on the science of sex determination. But there is still room for more.

 

from PRINT EDITION | Books and Arts

 

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