Differences in reaction to toxic substances vary considerably between species so that the value of these tests remains doubtful. Although thalidomide… - Richard D. Ryder

Their experiences may be more simple than ours, but are they less intense? Perhaps a caterpillar’s primitive pain when squashed is greater than our more sophisticated sufferings.

[The] habit of totalling pains and pleasures across individuals is one of the main errors in ethics today.

Sometimes captured from the great arboreal freedom of their jungle homes, monkeys are closely confined in cages only three or four feet square. … They can never sit or lie down on a flat, soft or yielding surface. Little wonder that by the time they are needed for the knife or the needle they are so crazed or inert that they are no longer representative examples of animal life. Psychologists who study the behaviour of thousands of such creatures annually, rarely make allowances for the fact that their pathetic subjects have been so deprived that they have become more like monsters than animals. Many people who have experienced close affectionate relationships with individuals of other species testify to the considerable potential for emotional and intellectual development that animals have. When properly cared for a pet dog or cat can develop great subtleties of behaviour that the laboratory animal never shows. Those who have been fortunate enough to closely observe unfrightened animals living in the wild are often struck by the complexity and richness of the life they lead. These positive pleasures the laboratory animal never knows; for him the same four white walls and the smell of disinfectant.