Humphrey roots his theory of consciousness in an excellent spot: it must have evolved as a result of natural selection. It conferred, and confers, advantage. Whilst not original in itself, this solid underpinning is followed by a truly original thesis. This is that consciousness has the effect of enhancing an animal’s sensations with the result that any potential subsequent behaviour becomes more urgent and more probable. Consciousness in effect provides its lucky owners with a zest for life that lifts them above more prosaic, non-conscious animals. Whether or not one agrees with the theory, it has the added advantage of being an account that jibes well with human concepts of soul and the like, whilst remaining explicitly materialist.