In this post at Discover Magazine (referencing a New Yorker article on Svante Pääbo), Razib Khan suggests that “Perhaps the difference between Neandertals and behaviorally modern humans was less about large between group differences in individual level traits, and more about the fact than Neandertals simply lacked the leadership cadre which behaviorally modern humans possessed“.
One of the other commenters beat me to it, but I too am inclined to suggest that perhaps what distinguishes “humanity” (from eg the apparently more cranially endowed Neandertals) is the “capacity” for suppressing one’s own intellect and immediate interests in favour of some socially determined doctrine and leadership. Perhaps this does lead to greater reproductive success for individuals who can affiliate with such groups, and perhaps those of us who are too “bright” to be fully “human” might then be well advised under most circumstances to mimic the general dimmness rather than fail the test of credulity and get pruned as defectors from the common interest.