Very interesting article by Claire Haworth et al. on the genetic influence of high intelligence. Apparently genetic differences explain approximately half the variance according to this study. BPS Research Digest does a nice job summarizing.
Haworth, C., Wright, M., Martin, N., Martin, N., Boomsma, D., Bartels, M., Posthuma, D., Davis, O., Brant, A., Corley, R., Hewitt, J., Iacono, W., McGue, M., Thompson, L., Hart, S., Petrill, S., Lubinski, D., & Plomin, R. (2009). A Twin Study of the Genetics of High Cognitive Ability Selected from 11,000 Twin Pairs in Six Studies from Four Countries. Behavior Genetics, 39 (4), 359-370 DOI: