[R]esearch into the nature of the relationship between Neanderthals and modern humans has implications for understanding the course of human evolution more generally. Of special interest, perhaps, is the light this research will shed on the origin and development of the human capacity for abstract thought, the single most definitive human characteristic. Did this ability appear all at once, fully formed? Or, was it gradually constructed over millions of years, species by species, with many different, perhaps more limited versions of this faculty having existed in the past? If so, our current mental capabilities are only the latest in an array of evolutionary experiments in this mode of adaptation. Seemingly, our version is the most sophisticated yet achieved, but it may not necessarily be the final version.