Whether or not animals feel is not altogether an easy question to answer. A human being has direct awareness only of the pains which he himself suffers. Our knowledge of the pains even of other human beings is only an inference from their words, and to a lesser extent their behaviors. Animals cannot tell us what they feel. We can, of course, study their bodily reactions to the kind of stimuli which would be painful to human beings and this has often been done. When such stimuli are applied to animals, their pupils dilate, their pulse rate and blood pressure rise, they may withdraw the stimulated limb and they may make struggling movements. Nevertheless it has been pointed out that none of these reactions can safely be taken as indications that the animal experiences pain because they can all be evoked when the parts of the body stimulated have been isolated from the higher nervous centres. Furthermore, when disease produces such an isolation in human beings the corresponding stimuli are painless. We must therefore look for other evidence as the capacity of animals to experience pain. Basically, all the nervous elements which underlie the experience of pain by human beings are to be found in all mammalian vertebrates at least; this is hardly surprising as pain is a response to a potentially harmful stimulus and is therefore of great biological importance for survival. Is there any reason, then, for supposing that animals, though equipped with all the necessary neurological structures, do not experience pain? Such a view would seem to presuppose a profound qualitative difference in the mental life of animals and men. The difference between the human and subhuman nervous system lies chiefly in the much greater development of the human forebrain. This would be significant in the present context only if there were reason to believe that it alone was correlated with the occurrence of conscious experiences. But much of our knowledge of the nervous regulation of consciousness is derived from experiments on animals. In everyday life we take it for granted that animals see and hear, and there seems no reason to suppose that they do not feel pain. So, while the reactions of the pupils, pulse rate and blood pressure mentioned above can in exceptional circumstances occur without the conscious experience of pain, it seems likely that in the intact animal they are indications that pain is being experienced.
单选题
Our knowledge of the pains animals feel can be obtained through