As we have seen, many non-human animals assist their own kin, or refrain from harming them. In some species this is true of unrelated animals as well. So the first steps toward ethics, like the first steps toward mathematics, were taken by our pre-human ancestors. Ethics starts with social animals prompted by their genes to help, and to refrain from injuring, selected other animals. On this base we must now superimpose the capacity to reason. Imagine a group of early humans interacting on the basis of kin and reciprocal altruism. From kin altruism we get a strongly developed tendency for parents to provide for and defend their offspring. Brothers and sisters would help each other to a lesser extent. Nieces, nephews, and cousins receive preferential treatment over non-relatives, to a degree that diminishes with the distance of the relationship. Nevertheless, in a small, cohesive community, all members might be related to some degree, and so kin altruism, supplemented perhaps by a weaker tendency toward group altruism, would lead to a general readiness to help other members of one's own group, rather than other humans belonging to a different group. Reciprocal altruism adds a different and to some extent conflicting current: gratitude to those who have helped in the past leads to friendship and mutual aid which is not based on close kinship; and hostility to "cheats" who do not reciprocate would counteract any general benevolence toward all members of the group. So far, this description could hold for non-human social animals as well as for human beings, although reciprocal altruism would be likely only among intelligent animals living in relatively stable groups. Gradually, as we evolved from our pre-human ancestors, our brains grew and we began to reason to a degree no other animal had achieved. We became better able to communicate with our fellows. Our language developed to the point at which it enabled us to refer to indefinitely many events, past, present, or future. We became more aware of ourselves as beings existing over time, with a past and a future, and more conscious of the patterns of our social life. We could reflect, and we could choose on the basis of our reflections. All this gave us, of course, tremendous advantages in the evolutionary competition for survival; but it also brought with it something which has not, so far as we can tell, occurred in any non-human society: the transformation of our evolved, genetically-based social practices into a system of rules and precepts guiding our conduct toward one another, supported by widely shared judgments of approval for those who do as the rules and precepts require, and disapproval for those who do not. Thus we arrived at a system of ethics or morality. The transformation must have been a gradual one, over hundreds of thousands of years. The difference made by reason in this transformation is the difference between responding with a friendly lick or an intimidating growl when another member of the group does or does not repay favors, and responding with an approving or a condemnatory judgment. Stating the difference this way leaves open how big a difference it is-some may think that ethical judgments really are no more than refined friendly licks and intimidating growls. One difference, though, is apparent: growls and licks leave little to be discussed; ethical judgments leave a lot. To judge, beings have to be capable of thinking and of defending the judgments they make. Once beings can think and talk, once they can challenge each other, and ask, "Why did you do that?" their growls and licks are evolving into ethical judgments.
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Reasoning in ethics is not limited to the negative task of rejecting custom as a source of ethical authority. We can progress toward rational settlement of disputes over ethics by taking the element of disinterestedness inherent in the idea of justifying one's conduct to society as a whole, and extending this into the principle that to be ethical, a decision must give equal weight to the interests of all affected by it. This would require me, in making an ethical judgment, to take my decision from a totally impartial point of view, a point of view from which I disregard my knowledge of whether I gain or lose by the action I am contemplating. One way of arriving at such a decision... is to imagine myself living the lives of all affected by my decision, and then ask what decision I prefer.
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The ancient Assyrian kings boastfully recorded in stone how they had tortured their non-Assyrian enemies and covered the valleys and mountains with their corpses. Romans looked on barbarians as beings who could be captured like animals for use as slaves or made to entertain the crowds by killing each other in the Colosseum. In modern times Europeans have stopped treating each other in this way, but less than two hundred years ago some still regarded Africans as outside the bounds of ethics, and therefore a resource which should be harvested and put to useful work. Similarly Australian aborigines were, to many early settlers from England, a kind of pest, to be hunted and killed whenever they proved troublesome. So the shift from a point of view that is disinterested between individuals within a group, but not between groups, to a point of view that is fully universal, is a tremendous change-so tremendous, in fact, that it is only just beginning to be accepted on the level of ethical reasoning and is still a long way from acceptance on the level of practice. Nevertheless, it is the direction in which moral thought has been going since ancient times. Is it an accident of history that this should be so, or is it the direction in which our capacity to reason leads us?
Why should our capacity to reason require anything more than disinterestedness within one's own group? Since the interests of my group will often be better served by ignoring the interests of members of other groups, the need for a public justification of conduct should require no more than this. Indeed, shouldn't we rather expect the need for public justification to prohibit justifications which give the interests of my group no more weight than the interests of other groups? This suggestion overlooks the autonomy of reasoning-the feature I have pictured as an escalator. If we do not understand what an escalator is, we might get on it intending to go a few meters, only to find that once we are on, it is difficult to avoid going all the way to the end. Similarly, once reasoning has got started it is hard to tell where it will stop. The idea of a disinterested defense of one's conduct emerges because of the social nature of human beings and the requirements of group living, but in the thought of reasoning beings, it takes on a logic of its own which leads to its extension beyond the bounds of the group.
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The circle of altruism has broadened from the family and tribe to the nation and race, and we are beginning to recognize that our obligations extend to all human beings. The process should not stop there. In my earlier book, Animal Liberation, I showed that it is as arbitrary to restrict the principle of equal consideration of interests to our own species as it would be to restrict it to our own race. The only justifiable stopping place for the expansion of altruism is the point at which all whose welfare can be affected by our actions are included within the circle of altruism. This means that all beings with the capacity to feel pleasure or pain should be included; we can improve their welfare by increasing their pleasures and diminishing their pains. The expansion of the moral circle should therefore be pushed out until it includes most animals. (I say "most" rather than "all" because there comes a point as we move down the evolutionary scale - oysters, perhaps, or even more rudimentary organisms-when it becomes doubtful if the creature we are dealing with is capable of feeling anything.) From an impartial point of view, the pleasures and pains of non-human animals are no less significant because the animals are not members of the species Homo sapiens. This does not mean that a human being and a mouse must always be treated equally, or that their lives are of equal value. Humans have interests-in ideas, in education, in their future plans that mice are not capable of having. It is only when we are comparing similar interests- of which the interest in avoiding pain is the most important example-that the principle of equal consideration of interests demands that we give equal weight to the interests of the human and the mouse.
Excerpts from Chapter 4 of "The Expanding Circle: Ethics, Evolution, and Moral Progress" by Peter Singer