To appear in Heams et al. (eds.), Handbook of Evolutionary Biology (provis. Title), Springer.

Please do not quote without permission. This is not the final version

that morality, or rather a moral sense – a recognition of the call of altruism and a propensity to obey – is something which is hard-wired into humans. It has been put there by natural selection in order to get us to work together socially or to cooperate. (Ruse 2002: 157)

In the same way as Richards and Ruse, Larry Arnhart thinks that human beings possess a natural moral sense (Arnhart 1998). But in contrast to his precedents, Arnhart does not reduce morality to altruism. For him, the moral sense is the natural extension of pro-social behaviour. It rests on a collection of desires shared by all human beings, such as the reciprocal desire of parents and their children to remain together or the desire for equality (1998: 89). In brief, the function of morality consists in facilitating positive interactions among individuals.

The list of different explanations of the genesis of morality is far from being complete. Taken together, they invoke all the mechanisms typically used in evolutionary theories: kin selection, direct and indirect reciprocity, group selection. However, given the scarce empirical and historical clues at our disposal, it is not clear how we should choose between these options. Without a doubt, they all contain a grain of truth because they refer to different aspects of the social dynamic of which morality is undeniably a part. A general impression that comes from reading these different explanatory models is that they are talking about highly speculative suppositions, the truth of which can never really be tested. This fact should not be ignored. But we should add three remarks. Firstly, even if the speculative explanations are not scientifically provable, it is legitimate and interesting to enquire into the genesis of morality. Secondly, the philosophers who are keen to point out the weaknesses of these models should not forget that the histories of the genesis of morality proposed by great philosophers (notably, Hobbes, Rousseau and Nietzsche) are even more speculative and much less realistic than those proposed by evolutionary ethicists. And, lastly, despite their divergences, all authors agree on a certain number of crucial elements. Most notably, there is the idea that morality appeared in the social and environmental context of our ancestors who lived in small communities where survival depended largely on the quality of internal cohesion in the group. Another point of agreement is the fact that mechanisms such as kin selection or reciprocity, the functioning of which is very precisely defined (as much at the conceptual level as at the mathematical level), have played a crucial role in the evolution of morality. These mechanisms are at the origin of the sociality of animal species that found themselves confronted with similar environmental challenges. Kin selection is an extremely powerful explanatory tool for understanding the attachment of parents to their progeny and, term)27, more generally (when it is understood in the wide sense of the for individuals belonging to the same group. Finally, evolutionary theorists underline the pertinence of the mathematical and information technology tools used in evolutionary game theory (Axelrod 1984, Maynard Smith 1982). With the help of these tools, it is possible to develop models that simulate competitive environments, the behavioural strategies that can be used in these environments, and the effect of natural selection on the diffusion of these strategies. These models are able to show the robustness, the stability and the positive global effects of helping behaviours in the socio-environmental conditions with which our ancestors were doubtless confronted (Fehr & Fischbacher 2003, Hammerstein 2003). There is thus nothing surprising in the fact that the psychological tendencies that favour this kind of behaviour have developed in human beings.

We have passed rapidly over a review of the evolutionary explanations of the origin of morality. We should note that descriptive ethics does not revolve only around this issue; it is also interested in moral beliefs and their diffusion in different human societies, as well as the

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