* At the time of this writing, a pair of papers has just been published highlighting the possible role of NOTCH2NL genes in human brain expansion. These genes appeared in our line three to four million years ago, just as our ancestors’ brains started to grow in leaps and bounds. Prior to the creation of our social-cognitive niche, these genes would have cost more than they were worth, and thus would not have proliferated. But after we started cooperating, the gains in social effectiveness enabled by greater intelligence easily offset the increased metabolic costs brought about by these brain-expanding genes.