The characteristics of a culture reflect work and on social relations, but they also depend on symbols. Unlike other species, for humans, symbols and the culturally constructed meanings on which they are based are the vehicles through which culture is perpetuated over generations. Because they are not organic, symbols can only be reproduced through human action. Our interaction with our environment is mediated by the symbols that give particular meanings to physical items, as are our determinations regarding the validity of what we think—how perceptions come to be treated as knowledge.