Halliday & Matthiessen (1999: 608):
Edelman (1992) relates this evolutionary perspective to the emergence of consciousness, which he explains in terms of a neurological account of brain structures. He interprets consciousness in what we can think of as semiotic terms, making a distinction between primary consciousness, which depends on the construal of scenes or images, and higher-order consciousness, which depends on the construal of meaning in language …
Edelman's account indicates the evolutionary value of the human potential for construing processes of consciousness. In contrast with mainstream cognitive science, Edelman makes language the central resource and relates it to the social construction of the self.
Our conception of the "meaning base" is fully compatible with this line of interpretation (cf. Halliday, 1995a): the human brain has evolved in the construction of a functioning model of "reality".