تآثیرات بر روی ارتباطات در مورد تولید مثل: تکامل فرهنگی باروری پایین

The cultural norms of traditional societies encourage behavior that is consistent with maximizing reproductive success but those of modern post-demographic transition societies do not. Newson et al (2005) proposed that this might be because interaction between kin is relatively less frequent in modern social networks. Assuming that people's evaluations of reproductive decisions are influenced by a desire to increase their inclusive fitness, they will be inclined to prefer their kin to make fitness-enhancing choices. Such a preference will encourage the emergence of pronatal cultural norms if social networks are dense with kin. Less pronatal norms will emerge if contact between kin makes up a small proportion of social interactions. This article reports evidence based on role-play studies that supports the assumption of the kin influence hypothesis that evaluations of reproductive decisions are influenced by a desire to increase inclusive fitness. It also presents a cultural evolutionary model demonstrating the long-term effect of declining kin interaction if people are more likely to encourage fitness-enhancing choices when interacting with their kin than with nonrelatives.

This article reports the results of a test of a key assumption of the “kin influence hypothesis” (Newson et al., 2005) that communications between kin are more likely than communications between non-kin to encourage behavior consistent with achieving reproductive success. Communication biased in this way would provide a means by which individuals can promote their inclusive fitness (Hamilton, 1964). The kin influence hypothesis suggests that, for any single interaction between close kin, there is a probability that this promotion will cause an attitude or behavioral change in the participants and that this change will tend in the direction of a more effective pursuit of reproductive success. Over many social interactions occurring over time in kinship-based networks, this mechanism can maintain pronatal cultural norms (i.e., norms that prescribe behavior consistent with maximizing reproductive success). But when interaction between kin is only a small proportion of social interaction, as in modern societies, cultural norms can evolve that allow behavior to become increasingly less consistent with the efficient conversion of resources to offspring. This mechanism could largely account for the demographic transition, the collapse in fertility that occurs as societies modernize (Borgerhoff Mulder, 1998). We present a cultural evolutionary model demonstrating how a reduction in contact between kin could result in the erosion of pronatal cultural norms if the content of communication is biased in the way suggested by the kin influence hypothesis. Cultural evolutionary models have shown that even very weak innate biases influencing the transmission of information within a population will cause the cultural norms of that population to change. Over time and many social interactions, culture evolves in a way that can be predicted by the direction of the bias (Boyd & Richerson, 1985, Durham, 1991 and Richerson & Boyd, 2005). Theoretical investigations of biased transmission have previously concentrated on “learning” biases of potential recipients of cultural information, which influence what learners adopt. The kin influence hypothesis assumes a “teaching” bias in the sources of cultural information. These influence the information available to learners.