Furthermore, each system has a distinctive identity that is constantly reproduced in its communication and depends on what is considered meaningful and what is not. If a system fails to maintain that identity, it ceases to exist as a system and dissolves back into the environment it emerged from. Luhmann called this process of reproduction from elements previously filtered from an over-complex environment autopoiesis (pronounced "auto-poy-E-sis"; literally: self-creation), using a term coined in cognitive biology by Chilean thinkers Humberto Maturana and Francisco Varela. Social systems are "operationally closed" in that while they use and rely on resources from their environment, those resources do not become part of the systems' operation. Both thought and digestion are important preconditions for communication, but neither appears in communication as such.