searchin' for our friend, homo economicus
I must have seen a zillion draft versions of this study floating around online, but here's a terrific preprint: “Economic man” in cross-cultural perspective: Behavioral experiments in 15 small-scale societies (Henrich, Boyd, Bowles, Camerer, Fehr, Gintis, McElreath, Alvard, Barr, Ensminger, Henrich, Hill, Gil-White, Gurven, Marlowe, Patton, and Tracer 2005 (!)). So looks like we're now pretty sure, culture affects cooperation, you can see it in social practices. It's a really neat study. The writeup in this version is terrific, they talk about implications for culture-gene evolution and have great statistical analysis of cultural factors on ultimatum game performance.