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June 12, 2005

Altruistic Punishment: part 2

I posted recently on altruistic punishment. My attention has been drawn to another study showing that altruism can be favoured by individual selection:

A. Sanchez and J. Cuesta: ‘Altruism may arise from individual selection’, Journal of Theoretical Biology, 21 July 2005 (forthcoming), 235, 233-40.

Abstract: The fact that humans cooperate with non-kin in large groups, or with people they will never meet again, is a long-standing evolutionary puzzle. Altruism, the capacity to perform costly acts that confer benefits on others, is at the core of cooperative behavior. Behavioral experiments show that humans have a predisposition to cooperate with others and to punish non-cooperators at personal cost (so-called strong reciprocity) which, according to standard evolutionary game theory arguments, cannot arise from selection acting on individuals. This has led to the suggestion of group and cultural selection as the only mechanisms that can explain the evolutionary origin of human altruism. We introduce an agent-based model inspired on the Ultimatum Game, that allows us to go beyond the limitations of standard evolutionary game theory and show that individual selection can indeed give rise to strong reciprocity. Our results are consistent with the existence of neural correlates of fairness and in good agreement with observations on humans and monkeys.

The full text requires subscription, but a substantially similar text is available as a free pdf here. I won’t comment in detail, but the model presented in this paper is rather simpler than the one in J. Fowler’s paper.

As I said in my previous post, I am sceptical about much of this game-theoretical work. It starts from the false assumption that (in Fowler’s words) ‘Human beings frequently cooperate with genetically unrelated strangers whom they will never meet again, even when such cooperation is individually costly’.

In support of such statements the theorists cite results of experimental economics which show that in games like Ultimatum people seldom follow a rationally self-interested strategy. But the setting for these experiments is quite artificial, and tells us little or nothing about the circumstances in which altruistic behaviour evolved. As Robert Trivers has put it, ‘It’s absurd - and I use the word advisedly - to imagine that we’ve evolved to respond to the specific situations these economists put us in, with complete anonymity and no chance to interact with partners a second time’ (Science, 303, 2/2/2004, 1131).

I don’t think that statements like Fowler’s are true even in modern societies, but that doesn’t really concern me. Many human traits are maladaptive in modern circumstances. To understand the evolution of any species-wide human trait, what matters is what happened in 100,000 years or so of paleolithic times. During this period all humans were hunter-gatherers.

The behaviour of hunter-gatherers in modern times is not a safe guide to their behaviour in the paleolithic - for one thing, modern hunter-gatherers are confined to marginal habitats like deserts and deep jungle - but it is the best guide we have. Based on studies of modern hunter-gatherers (see references below for a selection), I would make the following generalisations:

1. Hunter-gatherers usually live in small bands of between 20 and 50 individuals. There are seldom more than about 12 adult males in a band. Bands have an established territory with rights recognised by other groups.

2. Most if not all of the individuals in a band are related to each other by blood or marriage. There is usually a core group of siblings (see e.g. Lee p.51).

3. A number of bands make up a tribe of between a few hundred and a few thousand individuals. Bands within the same tribe have much the same language, customs and kinship system.

4. Marriage is usually between members of different bands within the same tribe. It is regulated by rules of exogamy and endogamy, though these seem to have been stricter and more elaborate among the Australian aborigines than elsewhere. Marriage between people of different tribes is less common but does occur, especially when the tribes are small (see e.g. Elkin p.79) Most hunter-gatherers are moderately polygamous, with the older or more successful men having more than one wife. Among the aborigines women are monopolised by the older men (Maddock p.57-60).

5. Individuals often stay in the same band for life, except that members of one sex will move to another band when married. However, it is possible for individuals or families to move from one band to another, or even to another tribe, provided this is approved by the receiving group (e.g. Spencer and Gillen, p.68). Bands as a whole may split up or merge in response to fluctuations of population or resources.

6. Day-to-day contacts are mainly within the same band. Members of different bands will sometimes visit, e.g. to meet relatives or to discuss marriage arrangements. This seems especially common among the Bushmen (Lee p.259) There may also be collective meetings between bands, such as the famous aboriginal corroborees (Elkin p.61).

7. Within a band, there is usually a good deal of cooperation, such as food-sharing. Band society has been described as ‘egalitarian’ (Boehm) but this should not be exaggerated. Individuals may differ greatly in prestige, influence, and number of relations. There are also differences in number of wives and reproductive success.

8. Relations between different bands range from friendly to hostile. Disputes can arise over territory, access to water or seasonal surpluses of food, and over women. Belief in witchcraft is also a major source of trouble. Disputes can lead to prolonged feuds and a series of tit-for-tat killings.

9. The cardinal principle of relations between bands is reciprocity (see e.g. Lee p.335-7). Reciprocity is a means of sharing fluctuating resources in a harsh environment. If a band is e.g. allowed access to another band’s territory to hunt, they will be expected to return the favour in due course.

10. Contrary to some assumptions, different hunter-gatherer tribes are not always in a state of hostility with each other. Tribes do not act as political or military units, so most bands will not have much contact with other tribes unless their territories border each other. Neighbouring bands from different tribes have relations ranging from friendly to hostile just like bands within the same tribe. People in border areas are often bilingual or have a common ‘pidgin’ dialect, and there is often trade and intermarriage between the tribes.

From these points I think it will be clear that the claim that ‘human beings frequently cooperate with genetically unrelated strangers whom they will never meet again’ is simply not true for hunter-gatherers. Within the band, cooperation is between individuals who are usually related, and never strangers. Between bands or tribes, cooperation is based on customary expectations of reciprocity. Failure to meet these expectations will result in withdrawal of cooperation or more active reprisals.

This is the background against which human behaviour has evolved. To the limited extent that behaviour is really altruistic, I see no reasons to appeal to evolutionary mechanisms other than inclusive fitness, reciprocal altruism (Trivers), or simple tit-for-tat cooperation (Axelrod and Hamilton). As to ‘altruistic punishment’, I doubt that there is much of that in hunter-gatherer societies, but I may come back to that.


C. Boehm: Hierarchy in the Forest, 2001
A. P. Elkin: The Australian Aborigines, 1964
L. Hobhouse, G. Wheeler, M. Ginsberg: The Material Culture and Social Institutions of the Simpler Peoples, 1915/1965
E. Leacock and R. Lee (eds): Politics and History in Band Societies, 1982
R. B. Lee: The !Kung San, 1979
K. Maddock: The Australian Aborigines, 1973
B. Spencer and F. Gillen: The Native Tribes of Central Australia, 1899
E. Westermarck: The Origin and Development of Moral Ideas, 1924

Posted by David B at 02:49 AM