Where X does not equal Y

Sex-difference research is a rhetorical football. Second-wave feminist thinkers initially challenged the very concept of difference as a way to undermine sex-difference research that reflected the cultural stereotypes underpinning discrimination. Today few would deny difference, but the debate has shifted to the cultural value around supposedly gendered characteristics. There have been major changes. Fifty years ago management culture required macho cut-throat competition and single-minded pursuit of the one best answer. Today managers require multitasking and pluralist thinking - qualities formerly attributed to women who lived in the permanently "distracted" domestic world.

But what does "difference" mean? Three distinct versions of "difference" are frequently confused. Is it either-or, as in having or not having a penis? Is it about overlapping curves? All men are not taller than all women; average height differs and about a quarter of women are taller than half the male population. Is it about frequency of the unusual? There are more geniuses, autistics, serial killers and dyslexics among males than females, but are these anomalies or are they extremes on a continuum - in which case we might ask what is peculiar, or lacking, about all the men who aren't Mozart or Jack the Ripper.

Although Susan Pinker does not always steer clear of these confusions about difference, she writes clearly and accessibly about the current state of sex-difference research in psychology and neuroscience. She is particularly good at discussing the subtle ways in which hormones, which both men and women produce, albeit in different quantities, facilitate behaviour and motivation in each sex. This is a neat counter to more commonly deterministic accounts. Pinker covers work in neuroscience that, to date, can identify the location rather than the operation of psychological processes, but she demonstrates the greater flexibility and more distributed localisation of many brain functions among females. Her own clinical work is with patients with attention-deficit disorder and attention-deficit hyperactivity disorder and she gives excellent in-depth descriptions of both the fragile nature of these conditions and the means by which individual sufferers overcome or compensate for them. Because most of her patients are male, this illuminates aspects of the "extreme male brain" hypothesis.

Pinker discusses the massive changes that have undermined traditional assumptions about sex difference. Hitherto underachieving females, victims of discrimination, are now at least equal and have frequently overtaken males in representation and academic performance in formerly male enclaves such as medicine, law, management and in most sciences apart from physics and engineering. Males have not fallen behind; females have caught up.

However, the book's narrative is structured around the question of why, given the choices now open to them, women do not apparently aspire to the same career heights as men. Pinker cites both hard data and anecdotes about women who retreat from high-powered jobs, often to spend time with young children, but also to pursue lower-paid careers in which they can "make a difference". She explores the suggestion of a hormone effect, but this is highly speculative.

While recognising the importance of this question, I find her example problematic. The "high-achieving males" against whom these women are compared are corporate lawyers who work more than 80 hours a week for obscenely large salaries, making money for others, and not always using their law degrees to improve justice. Are such people the epitome of human achievement? Or might they be regarded as pathological exemplars of an "extreme", localised contemporary culture? Rapid social change confronts us with just such challenges.