PLEASURES,PAINS AND ANIMAL-WELFARE - TOWARD A NATURAL-HISTORY OF AFFECT

In hedonic theories of motivation, 'motivational affective states' (MA Ss) are typically seen as adaptations which motivate certain types of behaviour, especially in situations where a flexible or learned respon se is more adaptive than a rigid or reflexive one. MASs can be negativ e leg unpleasant feelings of hunger or pain) or positive (eg pleasant feelings associated with eating and playing). Hedonic theories often p ortray negative and positive MASs as opposite ends of a one-dimensiona l scale. We suggest that natural selection has favoured negative and p ositive affect as separate processes to solve two different types of m otivational problems. We propose that negative MASs leg thirst, fear) evolved in response to 'need situations' where the fitness benefit of an action has increased, often because the action is needed to cope wi th a threat to survival or reproductive success. We propose that these negative MASs develop in response to a change in the body leg dehydra tion) or the environment (eg the approach of a predator) which creates the need for action, and that negative MASs can become intense and pr olonged if the threat to fitness is high and persistent. We propose th at positive MASs evolved in 'opportunity situations' where an action ( eg playing, exploring) has become advantageous because the fitness cos t of performing it has declined. We propose that these positive MASs o ccur during, or as a result of the performance of types of behaviour w hich are beneficial for fitness at a variety of times, not only when t hey are required to meet immediate needs; and that the pleasure inhere nt in the behaviour motivates the animal to perform it when the cost o f so doing is sufficiently low. Some behaviour leg eating) can be moti vated by both positive and negative affect. Other behaviour, such as p laying or fleeing from a predator, may be motivated largely by positiv e or negative affect alone. Our hypothesis needs to be tested, but we suggest that it corresponds well to common human experience. The hypot hesis provides a basis for predicting whether an aspect of animal mana gement is likely to cause strong and prolonged negative affect ('suffe ring', or to prevent animals from experiencing certain types of pleasu re. This distinction is important for bringing animal welfare assessme nt into line with ethical concerns.