My take on this:
- There are sex differences in ability, but not many, and the effect size is typically small* (Hyde 2005).
- Brain structure development is affected by a range of factors, environmental and genetic. For instance brain structure changes as a result of learning (e.g., Maguire et al, 2000). (And the phrase “hard-wired” is annoying.)
- A mean difference between groups, mean(group 1) > mean(group 2), on some measure does not imply that everyone in group 1 is better than everyone in group 2. So when selecting someone for a job, say, you could (a) grab a load of people with the sex which, on average, has (very slightly—see point 1) more of the ability you want and choose someone at random, or (b) you could choose someone who has more of the ability you want, and not focus on what genitalia they happen to possess.
- The designers of IQ tests hack their tests to remove sex differences, for instance the designers of the British Ability Scales (version 2) “used three strategies to test for fairness and to remove items likely to increase bias” (Hill, 2005). Blinkhorn (2005) says: “Where there are sex differences to be found, detailed study of the internal workings of the test tends to show why. That’s not based on instinct, but on my professional experience in designing gender-fair tests.”
Blinkhorn, S. (2005). Intelligence: a gender bender. Nature, 438, 31-32.
Hill, V. (2005). Through the Past Darkly: A Review of the British Ability Scales. Second Edition. Child and Adolescent Mental Health, 10, 87-98.
Hyde, J. S. (2005). The gender similarities hypothesis. American Psychologist, 60, 581-592.
Maguire, E. A.; Gadian, D. G.; Johnsrude, I. S.; Good, C. D.; Ashburner, J.; Frackowiak, R. S. & Frith, C. D. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proceedings of the National Academy of Sciences of the United States of America, 97, 4398-4403
* Women are presumably better at giving birth, with a large effect size.