The screen failed to find evidence for positive selection of two genes involved in brain development and cognition - ASPMM and Foxp2 - that studies have previously identified as positively selected genes in the human lineage. Zhang and Lahn agreed that the discrepancy likely results from differences in statistical power between the methods used in the current study and those used in previous work, which also incorporated polymorphism data.
Update:MIT Technology Review has more:
To Zhang's surprise and disappointment, the positively selected genes were not related to brain or cognitive function but to more mundane cellular housekeeping duties. "One explanation might be that the number of genes responsible for evolution of the human brain may be very small," Zhang speculates. ... "It is very rare that there will be enough changes in such a short lineage to tell us there is positive selection," says Lahn. "I'm very surprised that they claim these are positively selected genes. I would guess if they tried to publish each of these genes as an example of positive selection, there wouldn't be enough supporting data for the majority of them."