The following can be found on the American atheists website.

Ethics Without Gods
This essay was written by Frank Zindler, former President and current Board Member of American Atheists.

One of the first questions Atheists are asked by true believers and doubters alike is, “If you don’t believe in God, there’s nothing to prevent you from committing crimes, is there? Without the fear of hell-fire and eternal damnation, you can do anything you like, can’t you?”

Introduction
It is hard to believe that even intelligent and educated people could hold such an opinion, but they do! It seems never to have occurred to them that the Greeks and Romans, whose gods and goddesses were something less than paragons of virtue, nevertheless led lives not obviously worse than those of the Baptists of Alabama! Moreover, pagans such as Aristotle and Marcus Aurelius - although their systems are not suitable for us today - managed to produce ethical treatises of great sophistication, a sophistication rarely if ever equaled by Christian moralists.

The answer to the questions posed above is, of course, "Absolutely not!" The behavior of Atheists is subject to the same rules of sociology, psychology, and neurophysiology that govern the behavior of all members of our species, religionists included. Moreover, despite protestations to the contrary, we may assert as a general rule that when religionists practice ethical behavior, it isn't really due to their fear of hell-fire and damnation, nor is it due to their hopes of heaven. Ethical behavior - regardless of who the practitioner may be - results always from the same causes and is regulated by the same forces, and has nothing to do with the presence or absence of religious belief. The nature of these causes and forces is the subject of this essay.

Psychobiological Foundations
As human beings, we are social animals. Our sociality is the result of evolution, not choice. Natural selection has equipped us with nervous systems which are peculiarly sensitive to the emotional status of our fellows. Among our kind, emotions are contagious, and it is only the rare psychopathic mutants among us who can be happy in the midst of a sad society. It is in our nature to be happy in the midst of happiness, sad in the midst of sadness. It is in our nature, fortunately, to seek happiness for our fellows at the same time as we seek it for ourselves. Our happiness is greater when it is shared.

Nature also has provided us with nervous systems which are, to a considerable degree, imprintable. To be sure, this phenomenon is not as pronounced or as ineluctable as it is, say, in geese - where a newly hatched gosling can be "imprinted" to a toy train and will follow it to exhaustion, as if it were its mother. Nevertheless, some degree of imprinting is exhibited by humans. The human nervous system appears to retain its capacity for imprinting well into old age, and it is highly likely that the phenomenon known as "love-at-first-sight" is a form of imprinting. Imprinting is a form of attachment behavior, and it helps us to form strong interpersonal bonds. It is a major force which helps us to break through the ego barrier to create "significant others" whom we can love as much as ourselves. These two characteristics of our nervous system - emotional suggestibility and attachment imprintability - although they are the foundation of all altruistic behavior and art, are thoroughly compatible with the selfishness characteristic of all behaviors created by the process of natural selection. That is to say, to a large extent behaviors which satisfy ourselves will be found, simultaneously, to satisfy our fellows, and vice-versa.

This should not surprise us when we consider that among the societies of our nearest primate cousins, the great apes, social behavior is not chaotic, even if gorillas do lack the Ten Commandments! The young chimpanzee does not need an oracle to tell it to honor its mother and to refrain from killing its brothers and sisters. Of course, family squabbles and even murder have been observed in ape societies, but such behaviors are exceptions, not the norm. So too it is in human societies, everywhere and at all times.

The African apes - whose genes are ninety-eight to ninety-nine percent identical to ours - go about their lives as social animals, cooperating in the living of life, entirely without the benefit of clergy and without the commandments of Exodus, Leviticus, or Deuteronomy. It is further cheering to learn that sociobiologists have even observed altruistic behavior among troops of baboons. More than once, in troops attacked by leopards, aged, post reproduction-age males have been observed to linger at the rear of the escaping troop and to engage the leopard in what often amounts to a suicidal fight. As the old male delays the leopard's pursuit by sacrificing his very life, the females and young escape and live to fulfill their several destinies. The heroism which we see acted out, from time to time, by our fellow men and women, is far older than their religions. Long before the gods were created by the fear-filled minds of our less courageous ancestors, heroism and acts of self-sacrificing love existed. They did not require a supernatural excuse then, nor do they require one now.

Given the general fact, then, that evolution has equipped us with nervous systems biased in favor of social, rather than antisocial, behaviors, is it not true, nevertheless, that antisocial behavior does exist, and it exists in amounts greater than a reasonable ethicist would find tolerable? Alas, this is true. But it is true largely because we live in worlds far more complex than the Paleolithic world in which our nervous systems originated. To understand the ethical significance of this fact, we must digress a bit and review the evolutionary history of human behavior.

A Digression
Today, heredity can control our behavior in only the most general of ways, it cannot dictate precise behaviors appropriate for infinitely varied circumstances. In our world, heredity needs help.

In the world of a fruit fly, by contrast, the problems to be solved are few in number and highly predictable in nature. Consequently, a fruit fly's brain is largely "hard-wired" by heredity. That is to say, most behaviors result from environmental activation of nerve circuits which are formed automatically by the time of emergence of the adult fly. This is an extreme example of what is called instinctual behavior. Each behavior is coded for by a gene or genes which predispose the nervous system to develop certain types of circuits and not others, and where it is all but impossible to act contrary to the genetically predetermined script.

The world of a mammal - say a fox - is much more complex and unpredictable than that of the fruit fly. Consequently, the fox is born with only a portion of its neuronal circuitry hard-wired. Many of its neurons remain "plastic" throughout life. That is, they may or may not hook up with each other in functional circuits, depending upon environmental circumstances. Learned behavior is behavior which results from activation of these environmentally conditioned circuits. Learning allows the individual mammal to learn - by trial and error - greater numbers of adaptive behaviors than could be transmitted by heredity. A fox would be wall-to-wall genes if all its behaviors were specified genetically.

With the evolution of humans, however, environmental complexity increased out of all proportion to the genetic and neuronal changes distinguishing us from our simian ancestors. This partly was due to the fact that our species evolved in a geologic period of great climatic flux - the Ice Ages - and partly was due to the fact that our behaviors themselves began to change our environment. The changed environment in turn created new problems to be solved. Their solutions further changed the environment, and so on. Thus, the discovery of fire led to the burning of trees and forests, which led to destruction of local water supplies and watersheds, which led to the development of architecture with which to build aqueducts, which led to laws concerning water-rights, which led to international strife, and on and on.

Given such complexity, even the ability to learn new behaviors is, by itself, inadequate. If trial and error were the only means, most people would die of old age before they would succeed in rediscovering fire or reinventing the wheel. As a substitute for instinct and to increase the efficiency of learning, mankind developed culture. The ability to teach - as well as to learn - evolved, and trial-and-error learning became a method of last resort.

By transmission of culture - passing on the sum total of the learned behaviors common to a population - we can do what Darwinian genetic selection would not allow: we can inherit acquired characteristics. The wheel once having been invented, its manufacture and use can be passed down through the generations. Culture can adapt to change much faster than genes can, and this provides for finely tuned responses to environmental disturbances and upheavals. By means of cultural transmission, those behaviors which have proven useful in the past can be taught quickly to the young, so that adaptation to life - say on the Greenland ice cap - can be assured.

Even so, cultural transmission tends to be rigid: it took over one hundred thousand years to advance to chipping both sides of the hand-ax! Cultural mutations, like genetic mutations, tend more often than not to be harmful, and both are resisted - the former by cultural conservatism, the latter by natural selection. But changes do creep in faster than the rate of genetic change, and cultures slowly evolve. Even that cultural dinosaur known as the Catholic Church - despite its claim to be the unchanging repository of truth and "correct" behavior - has changed greatly since its beginning.

Incidentally, it is at this hand-ax stage of behavioral evolution at which most of the religions of today are still stuck. Our inflexible, absolutist moral codes also are fixated at this stage. The Ten Commandments are the moral counterpart of the "here's-how-you-rub-the-sticks-together" phase of technological evolution. If the only type of fire you want is one to heat your cave and cook your clams, the stick-rubbing method suffices. But if you want a fire to propel your jet-plane, some changes have to be made.

So, too, with the transmission of moral behavior. If we are to live lives which are as complex socially as jet-planes are complex technologically, we need something more than the Ten Commandments. We cannot base our moral code upon arbitrary and capricious fiats reported to us by persons claiming to be privy to the intentions of the denizens of Sinai or Olympus. Our ethics can be based neither upon fictions concerning the nature of humankind nor upon fake reports concerning the desires of the deities. Our ethics must be firmly planted in the soil of scientific self-knowledge. They must be improvable and adaptable.

Where then, and with what, shall we begin?

Back to Ethics
Plato showed long ago, in his dialogue Euthyphro, that we cannot depend upon the moral fiats of a deity. Plato asked if the commandments of a god were "good" simply because a god had commanded them or because the god recognized what was good and commanded the action accordingly. If something is good simply because a god has commanded it, anything could be considered good. There would be no way of predicting what in particular the god might desire next, and it would be entirely meaningless to assert that "God is good." Bashing babies with rocks would be just as likely to be "good" as would the principle "Love your enemies." (It would appear that the "goodness" of the god of the Old Testament is entirely of this sort.)

On the other hand, if a god's commandments are based on a knowledge of the inherent goodness of an act, we are faced with the realization that there is a standard of goodness independent of the god and we must admit that he cannot be the source of morality. In our quest for the good, we can bypass the god and go to his source!

Given, then, that gods a priori cannot be the source of ethical principles, we must seek such principles in the world in which we have evolved. We must find the sublime in the mundane. What precept might we adopt?

The principle of "enlightened self-interest" is an excellent first approximation to an ethical principle which is both consistent with what we know of human nature and is relevant to the problems of life in a complex society. Let us examine this principle.

First we must distinguish between "enlightened" and "unenlightened" self-interest. Let's take an extreme example for illustration. Suppose you lived a totally selfish life of immediate gratification of every desire. Suppose that whenever someone else had something you wanted, you took it for yourself.

It wouldn't be long at all before everyone would be up in arms against you, and you would have to spend all your waking hours fending off reprisals. Depending upon how outrageous your activity had been, you might very well lose your life in an orgy of neighborly revenge. The life of total but unenlightened self-interest might be exciting and pleasant as long as it lasts - but it is not likely to last long.

The person who practices "enlightened" self-interest, by contrast, is the person whose behavioral strategy simultaneously maximizes both the intensity and duration of personal gratification. An enlightened strategy will be one which, when practiced over a long span of time, will generate ever greater amounts and varieties of pleasures and satisfactions.

How is this to be done?

It is obvious that more is to be gained by cooperating with others than by acts of isolated egoism. One man with a rock cannot kill a buffalo for dinner. But a group of men or women, with lots of rocks, can drive the beast off a cliff and - even after dividing the meat up among them - will still have more to eat than they would have had without cooperation.

But cooperation is a two-way street. If you cooperate with several others to kill buffaloes, and each time they drive you away from the kill and eat it themselves, you will quickly take your services elsewhere, and you will leave the ingrates to stumble along without the Paleolithic equivalent of a fourth-for-bridge. Cooperation implies reciprocity.

Justice has its roots in the problem of determining fairness and reciprocity in cooperation. If I cooperate with you in tilling your field of corn, how much of the corn is due me at harvest time? When there is justice, cooperation operates at maximal efficiency, and the fruits of cooperation become ever more desirable. Thus, enlightened self-interest entails a desire for justice. With justice and with cooperation, we can have symphonies. Without it, we haven't even a song.

Let us bring this essay back to the point of our departure. Because we have the nervous systems of social animals, we are generally happier in the company of our fellow creatures than alone. Because we are emotionally suggestible, as we practice enlightened self-interest we usually will be wise to choose behaviors which will make others happy and willing to cooperate and accept us - for their happiness will reflect back upon us and intensify our own happiness. On the other hand, actions which harm others and make them unhappy - even if they do not trigger overt retaliation which decreases our happiness - will create an emotional milieu which, because of our suggestibility, will make us less happy.

Because our nervous systems are imprintable, we are able not only to fall in love at first sight, we are able to love objects and ideals as well as people, and we are able to love with variable intensities. Like the gosling attracted to the toy train, we are pulled forward by the desire for love. Unlike the gosling's "love," however, our love is to a considerable extent shapeable by experience and is capable of being educated. A major aim of enlightened self-interest, surely, is to give and receive love, both sexual and nonsexual. As a general - though not absolute - rule, we must choose those behaviors which will be likely to bring us love and acceptance, and we must eschew those behaviors which will not.

Another aim of enlightened self-interest is to seek beauty in all its forms, to preserve and prolong its resonance between the world outside and that within. Beauty and love are but different facets of the same jewel: love is beautiful, and we love beauty.

The experience of love and beauty, however, is a passive function of the mind. How much greater is the joy which comes from creating beauty. How delicious it is to exercise actively our creative powers to engender that which can be loved. Paints and pianos are not necessarily prerequisites for the exercise of creativity: Whenever we transform the raw materials of existence in such a way that we leave them better than they were when we found them, we have been creative.

The task of moral education, then, is not to inculcate by rote great lists of do's and don'ts, but rather to help people to predict the consequences of actions being considered. What are the long-term as well as immediate rewards and draw-backs of the acts? Will an act increase or decrease one's chances of experiencing the hedonic triad of love, beauty, and creativity?

Thus it happens, when the Atheist approaches the problem of finding natural grounds for human morals and establishing a nonsuperstitious basis for behavior, that it appears as though nature has already solved the problem to a great extent. Indeed, it appears as though the problem of establishing a natural, humanistic basis for ethical behavior is not much of a problem at all. It is in our natures to desire love, to seek beauty, and to thrill at the act of creation. The labyrinthine complexity we see when we examine traditional moral codes does not arise of necessity: it is largely the result of vain attempts to accommodate human needs and nature to the whimsical totems and taboos of the demons and deities who emerged with us from our cave-dwellings at the end of the Paleolithic Era - and have haunted our houses ever since.

Link : http://atheists.org/activism/resources/ethics