Doctor Feelgood: the new science of positive psychology

Martin Seligman and others pioneers use hard science in a new field of experimental psychology.

Of the six universal emotions, four -- anger, fear, disgust and sadness -- are negative and only one, joy, is positive. (The sixth, surprise, is neutral.) According to the psychologist Daniel Nettle, author of Happiness, and one of the Royal Institution lecturers, the negative emotions each tell us "something bad has happened" and suggest a different course of action. Fear tells us danger is near, so run away. Anger prompts us to deter aggressors. Sadness warns us to be cautious and save energy, while disgust urges us to avoid contamination.
Joy, according to Nettle, simply tells us, "something good has happened, don't change anything". The evolutionary role of pleasure was to encourage activity that was good for survival, such as eating and having sex. But unlike negative emotions, which are often persistent, joy tends to be short-lived. We soon get sick of cream cakes or blasé about our pay rise.

Happiness? Times Online.