The origins and development of aesthetics.

All people (and some other animals) have aesthetic responses to sensory stimulation, responses of emotional pleasure or displeasure. These emotions vary from one person and culture to another, yet they share a common mechanism. To survive, an adaptive animal (as opposed to a tropic animal) needs to become comfortable with normality and to have slight abnormalities draw attention to themselves. Walking through a jungle you need to notice a tiger from a single stripe: if you must wait to see the whole animal, you are unlikely to survive. In , the brain's adaptive neurochemistry does this naturally, partly because the brain's neuronal networks are structured to react efficiently to fractal structures, structures that shape much of nature. In addition, previous associations may turn a slight variation from normal into feelings of either pleasure or danger. The details of these responses-what is normal and what variations feel like-will depend upon an individual's experience, but the mechanism is the same, no matter whether a person is tasting a wine, seeing a face or landscape, or hearing a song. This article is part of the theme issue 'Sensing and feeling: an integrative approach to sensory processing and emotional experience'.