Science this week has a long profile of Bruce Lahn, written by Michael Balter. What I find most remarkable is how some high-profile geneticists are willing to stand up against the idea that humans could be subject to natural selection.
A sidebar accompanying the profile reviews the lack of evidence for a connection between ASPM variants and IQ in two large studies. It also mentions the possible sperm-brain connection:
But genome researcher Chris Ponting of the University of Oxford, U.K., notes that microcephalin and ASPM are also expressed outside the brain. In last May's issue of Bioinformatics, he reported that part of ASPM's DNA sequence resembles that of genes involved in the function of flagella, which propel sperm. Earlier work had shown that ASPM is expressed during sperm production. Ponting suggests that natural selection might have acted on flagellar function rather than brain growth. "These genes could well have many functions in many parts of the body," Ponting says, "and any one of these could have driven their adaptive sequence changes."
This is an interesting suggestion considering the high rate of evolution of ASPM during primate evolution -- it tracks like a sperm production gene in that regard. But it doesn't explain microcephalin or the other brain-expressed genes enriched for positive selection on the human lineage. So if ASPM itself isn't under selection for brain function, plenty of other genes have been.
One thing is for sure -- with the strength of selection on ASPM, it has to be strongly correlated with something that influences fitness.