... fetus or animal behaves a certain way that it is reacting to what it considers to be good or bad. We can not let this discourage our inquiry however, because in the same way, we cannot even be certain that another adult human is really feeling anything that we think they are. Maybe they cry and so it seems as if they are sad, but they cry when they are not sad, or they just cry at random. If we must make judgments about a thing's moral status, we must assume that our methods for testing whether a thing can feel good and bad are correct. If a thing has a nervous system, we generally consider it to have moral status because it can prefer the feeling of sensory pleasure over pain. Both the fetus (after some short time when it develops a nervous system) and an animal meet this ...

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