Thus, when Philippe Rushton and his associates studied ASPM, they looked to see whether its variants co-varied with indices of general intelligence, either IQ or brain size. When nothing turned up, they concluded that any relationship to mental ability must be a weak one (Rushton et al., 2007).
In an e-mail, Philippe Rushton went on to explain that:
… these [IQ] tests are highly predictive of work performance, which is often evaluated over long time periods and likely gives plenty of room for excellence from the unmeasured qualities you expect are important. For example, Salgado, Anderson, Moscoso, Bertua, and Fruyt (2003) demonstrated the international generalizability of GMA across 10 member countries of the European Community (EC), thus contradicting the view that criterion-related validity is moderated by differences in a nation's culture, religion, language, socioeconomic level, or employment legislation. They found scores predicted job performance ratings 0.62 and training success 0.54.
Yes, these are high correlations, but they still leave a lot of variability unexplained. Moreover, in the case of ASPM, we may be looking at something that improves mental performance on a very specific task—one that most people no longer engage in. How often do people take dictation nowadays?
And there is evidence that g is not everything. As Steve Sailer notes:
… g, like any successful reductionist theory, has its limits. Males and females, while similar on mean g (but not on the standard deviation of g: guys predominate among both eggheads and knuckleheads), differ on several specific cognitive talents. Men, Jensen reports in passing, tend to be better at visual-spatial skills (especially at mentally rotating 3-d objects) and at mathematical reasoning. Women are generally superior at short-term memory, perceptual speed, and verbal fluency. Since the male sex is stronger at logically manipulating objects, while the female sex prevails at social awareness, that explains why most nerds are male, while most "berms" (anti-nerds adept at interpersonal skills and fashion) are female. Beyond cognition, there are other profound sex dissimilarities in personality, motivation, and physiology.
Clearly, if the new ASPM variant does have an effect on the brain, it cannot be a general one that influences all brain tissues. This was already being pointed out at the time of its discovery by anthropologist John Hawks:
Nobody currently knows what these alleles may have done. It seems likely that people with the allele have some sort of cognitive advantage, which ultimately translates into a reproductive benefit. This advantage is probably not associated with greater brain sizes, because the average brain size appears not to have changed appreciably during the past 30,000 years.
So what is going on now? Nothing really. An article came out a year ago about a possible relationship between the old ASPM variant and tonal languages like Chinese (Dediu & Ladd, 2007). But this was the sort of blackboard musing that I like to indulge in. Currently, as far as I know, no lab research is being done.
References
Dediu D.L. & Ladd D.R. (2007). Linguistic tone is related to the population frequency of the adaptive haplogroups of two brain size genes, ASPM and Microcephalin. Proc. Natl. Acad. Sci. U.S.A., 104 (26), 10944–9. doi:10.1073/pnas.0610848104.
Rushton, J.P., Vernon, PA.., Bons, T.A. (2007). No evidence that polymorphisms of brain regulator genes Microcephalin and ASPM are associated with general mental ability, head circumference or altruism. Biology Letters-UK, 3, 157–60.
Salgado, J. F., Anderson, N., Moscoso, S., Bertua, C., & Fruyt, F. D. (2003). International validity generalization of GMA and cognitive abilities: A European community meta-analysis. Personnel Psychology, 56, 573-605.