Modern human communication is dominated by language, an extremely unusual mode that appears to be intimately tied to our equally unusual symbolic form of thought as well as to our unique speech apparatus. Some view language as gradually acquired under natural selection, others as a sudden and recent acquisition. The disagreement arises because language leaves no direct traces in the material record, and anatomical proxies for speech such as cranial base or hyoid architecture have proven equivocal. Similarly, even sophisticated Paleolithic stone tools cannot be taken as proxies for symbolic thought, as cognitively complex as their makers may have been. Unequivocal evidence for symbolic thought-and by extension, for language-is only found in overtly symbolic objects, which first occur significantly after the appearance of Homo sapiens. This suggests that the biological substrate for symbolic thought resulted from the major developmental reorganization that gave rise to our anatomically distinctive species, but that the new potential was not exploited until it was exaptively released by a cultural stimulus, plausibly the invention of language. By this time, the vocal apparatus necessary for speech was already in place.
