 Secondary consciousness is seen in animals with semantic capabilities, such as the four great apes.It is present in its richest form in the human species, which is unique in possessing complex language made up of syntax and semantics.In considering how the neural mechanisms underlying primary consciousness arose and were maintained during evolution, it is proposed that at some time around the divergence of reptiles into mammals and then into birds, the embryological development of large numbers of new reciprocal connections allowed rich re-entrant activity to take place between the more posterior brain systems carrying out perceptual categorization and the more frontally located systems responsible for value-category memory.