Culture Magazine

Contra Deus Ex Machina

By Cris

In Ars Poetica (“The Art of Poetry”), the great Roman lyricist Horace counsels against using gods to resolve thorny plots. The deus ex machina is simply too tidy and unbelievable. When gods swoop in to save the day, the mundane becomes sacred. Metaphysics to the rescue.

Contra Deus ex Machina

I was reminded of Horace’s enduring wisdom by two recent studies; the first on cooperation and second on punishment. Both are major contributions to our understanding of human altruism and collective action. Neither invokes the magic of gods.

In the “Evolution of Direct Reciprocity,” Andrew Delton and colleagues demonstrate that humans are naturally generous even to strangers and that such generosity is evolutionarily advantageous. A co-author of the July 25 PNAS study, Leda Cosmides, explains why humans can afford to be generous (i.e., incur costs) even when interaction might be a one-time affair:

There are two errors a cooperating animal can make, and one is more costly than the other. Believing that you will never meet this individual again, you might choose to benefit yourself at his expense –– only to find out later that the relationship could have been open-ended. If you make this error, you lose out on all the benefits you might have had from a long-term, perhaps life-long, cooperative relationship. This is an extraordinarily costly error to make.

The other error is to mistakenly assume that you will have additional interactions with the other individual and therefore cooperate with him, only to find out later that it wasn’t necessary. Although you were “unnecessarily” nice in that one interaction, the cost of this error is relatively small. Without knowing why, the mind is skewed to be generous to make sure we find and cement all those valuable, long-term relationships.

This is the restrained and mathematical kind of evolutionary psychology we can believe in.

In “Punishment Sustains Large-Scale Cooperation in Prestate Warfare,” Sarah Mathew and Robert Boyd find that profane punishment solves the free-rider problem that so exorcizes some evolutionary theorists of religion:

Understanding cooperation and punishment in small-scale societies is crucial for explaining the origins of human cooperation. We studied warfare among the Turkana, a politically uncentralized, egalitarian, nomadic pastoral society in East Africa.

Based on a representative sample of 88 recent raids, we show that the Turkana sustain costly cooperation in combat at a remarkably large scale, at least in part, through punishment of free-riders. Raiding parties comprised several hundred warriors and participants are not kin or day-to-day interactants. Warriors incur substantial risk of death and produce collective benefits. Cowardice and desertions occur, and are punished by community-imposed sanctions, including collective corporal punishment and fines. Furthermore, Turkana norms governing warfare benefit the ethnolinguistic group, a population of a half-million people, at the expense of smaller social groupings.

These results challenge current views that punishment is unimportant in small-scale societies and that human cooperation evolved in small groups of kin and familiar individuals. Instead, these results suggest that cooperation at the larger scale of ethnolinguistic units enforced by third-party sanctions could have a deep evolutionary history in the human species.

Large-scale cooperation, in other words, can revolve around something other than systematic religion or supernatural punishment. Shared language and ethnicity — along with earthly rewards (and beatings) — seem to work just fine.

We don’t need a group level or adaptive deus ex machina to explain the extraordinary success of ordinary humans. Parsimony to the rescue.


Delton AW, Krasnow MM, Cosmides L, & Tooby J (2011). Evolution of direct reciprocity under uncertainty can explain human generosity in one-shot encounters. Proceedings of the National Academy of Sciences of the United States of America PMID: 21788489

Mathew S, & Boyd R (2011). Punishment sustains large-scale cooperation in prestate warfare. Proceedings of the National Academy of Sciences of the United States of America, 108 (28), 11375-80 PMID: 21670285


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