Halliday & Matthiessen (1999: 607):
Neurobiologists interpret the evolution of the brain in vertebrate species as the evolution of the species' potential for constructing reality (Jerison, 1973 (1992); Edelman, 1992). Evolution brings about a constant change in the organism's relation to its environment; this relationship becomes increasingly complex, so that the organism's model of the environment has to become increasingly complex in its turn. This, it is suggested, is what "drives" the evolution of more and more complex brain structures.