There are two classes of arguments (I am simplifying, of course) that I have heard proposed in defense of religious beliefs.

First, there are theological arguments, which aim essentially at establishing that this or that religious belief is true, in some sense of the word. I have expressed my reservations about these arguments on other occasions and I will not return to the subject here.

Then there are those that I will call social arguments, which try to establish the social value of religious beliefs — that is, they try to establish that, independent of theological plausibility, religion is useful to society. A large part of these arguments rests on the idea of morality.

They say that without a religious underpinning, there is no possible a priori basis for morality; consequently, all moral prescriptions would degenerate into the most abject relativism. Religious moral prescriptions, on the other hand, come directly from God and are, because of this, absolute — if not quite a Kantian categorical imperative, at least absolute for the members of a particular religion.

In my view, the latter position is mistaken in two complementary and probably related aspects. On one hand, it overestimates the stability and inevitability of religious morality; on the other hand, it overestimates the relativism of any cultural form of morality.

Religious morality is much more variable than it is made out to be, and much more adaptable to mutable social circumstances.

Just to take a few examples, abortion at any time is currently considered a sin, and therefore immoral by most Christian denominations. However, until about 150 years ago, all major churches unquestioningly accepted abortion before “”quickening,”” roughly at the end of the second trimester. These days, we consider money loans to be a normal part of business activity, but for a long time, the Catholic church considered loaning money at interest a sin.

The other overstatement — that a cultural notion of morality would invariably lead to relativism — is more interesting. It is certainly true that if we consider morality as a cultural notion and take a synchronic point of view, there is reason to believe that, say, considering murder as moral would make as much sense as considering it immoral and that any cultural notion of morality is relativistic.

Looking at things diachronically (i.e. historically), however, the picture changes considerably. A simple and by no means complete model can be posited viewing morality as an evolutionary property of a culture, which interacts with its social environment much like an animal species evolves in an ecosystem.

The survival of the culture requires that certain stable relations exist among the members of a community and consequently that moral norms take certain directions rather than others. To stay with the example above, it is perfectly possible to conceive of a culture that encourages murder, but it is just as obvious that such a culture would not survive for a long time.

Similarly, a society in which incest is not immoral would degenerate into disconnected groups of families closed into themselves and the social exchanges that are necessary for the formation of larger groups would be impossible. It is interesting to note in this respect that, according to anthropologist Claude Levi-Strauss, in several “”primitive”” tribes, incest is not seen as immoral, but as socially ridiculous.

With the necessary additions and clarifications, cultural evolution explains how a laic, strictly cultural morality can arise without being completely arbitrary. Nevertheless, evolution based on pure functionalism is far too simplistic to explain even partially the detailed aspects of morality.

Endless complications arise. For one thing, morality is often concerned with the long-term benefits of the group rather than with the short-term benefits to the individual and, as a consequence, a system of enforcement must be created. Police enforcement works only partially, while religion (with its idea of an endlessly watching God) and tradition offer, in many cases, an ideal enforcement framework.

With religion and tradition, however, comes a considerable moral inertia: Moral precepts tend to remain the same in the face of drastic changes in the condition that caused them to be created to begin with.

Examples of this phenomenon abound, from the resistance (quickly overturned, fortunately) to painless child delivery in the 19th century to the permanence of ancient norms of sexual conduct in an age of diffused and safe contraceptives.

Of course, this model is still partial, and I doubt that a model simpler than the complete cultural anthropology of a society can explain all aspects of morality.

The point, however, is that there are ways to explain how certain moral codes are common to almost all populations on earth, and how morality can be more than just a system of arbitrary convention without resorting to the metaphysical scaffolding that religions encourage us to accept uncritically.