The basic cultural evolutionary mechanism is a “teaching bias” in the terms of Boyd and Richerson (1985). Most people normally espouse values, norms, and behaviors similar to those held by others in their community. Thus, younger people’s values, norms, and behaviors substantially refl ect those of the previous generation, and culture includes an inertial effect simply by consequence of people learning from each other. However, the same people when communicating with a close relative are slightly more likely to express variants of conventional norms that favor reproductive success, while those communicating with a friend, coworker, or other non-relative are slightly more likely to emphasize other goals. Newson et al. (2007) report role-play experiments that show this effect and also present a theoretical model that indicates how a decrease in the ratio of relatives to non-relatives in a social network can lead to the decline of norms favoring inclusive fi tness derived from the biased teaching effect. The rate of decline depends upon the strength of the teaching bias and on the ratio of kin to non-kin in social networks. But, even if the change in network structure is rapid and the teaching bias is quite strong, it is still likely to take several generations for a population to approximate a new equilibrium in norms related to reproduction.Via @GarrettJones on Twitter. The paper is interesting throughout.