In this regard, it is conceivable that one or more of the human-specific NR2E1 sites identified in the present study may have been fixed by positive selection in a manner similar to that proposed for ASPM, which is mutated in some patients with microcephaly (Bond et al. 2003; Kumar et al. 2004; Woods et al. 2005). This evidence concerns the gene ASPM and microcephaly.