Yan Minhua, Mathew Sarah, Boyd Robert
School of Human Evolution and Social Change, Arizona State University, Cady Mall, Tempe 85281 AZ, USA.
Institute of Human Origins, Arizona State University, Rob and Melani Walton Center for Planetary Health, Tempe, 85281 AZ, USA.
PNAS Nexus. 2023 Feb 23;2(3):pgad054. doi: 10.1093/pnasnexus/pgad054. eCollection 2023 Mar.
Differences in social norms are a key source of behavioral variation among human populations. It is widely assumed that a vast range of behaviors, even deleterious ones, can persist as long as they are locally common because deviants suffer coordination failures and social sanctions. Previous models have confirmed this intuition, showing that different populations may exhibit different norms even if they face similar environmental pressures or are linked by migration. Crucially, these studies have modeled norms as having a few discrete variants. Many norms, however, have a continuous range of variants. Here we present a mathematical model of the evolutionary dynamics of continuously varying norms and show that when the social payoffs of the behavioral options vary continuously the pressure to do what others do does not result in multiple stable equilibria. Instead, factors such as environmental pressure, individual preferences, moral beliefs, and cognitive attractors determine the outcome even if their effects are weak, and absent such factors populations linked by migration converge to the same norm. The results suggest that the content of norms across human societies is less arbitrary or historically constrained than previously assumed. Instead, there is greater scope for norms to evolve towards optimal individual or group-level solutions. Our findings also suggest that cooperative norms such as those that increase contributions to public goods might require evolved moral preferences, and not just social sanctions on deviants, to be stable.
社会规范的差异是人类群体行为变异的一个关键来源。人们普遍认为，即使是有害的行为，只要在当地普遍存在，就可能持续下去，因为偏离者会遭遇协调失败和社会制裁。先前的模型证实了这种直觉，表明不同群体可能表现出不同的规范，即使它们面临相似的环境压力或通过迁移相互联系。至关重要的是，这些研究将规范建模为具有几个离散的变体。然而，许多规范具有连续范围的变体。在这里，我们提出了一个关于连续变化规范的进化动力学的数学模型，并表明当行为选择的社会收益连续变化时，模仿他人行为的压力不会导致多个稳定均衡。相反，环境压力、个人偏好、道德信念和认知吸引子等因素决定了结果，即使它们的影响微弱，并且在没有这些因素的情况下，通过迁移相互联系的群体趋向于相同的规范。结果表明，人类社会中规范的内容比以前假设的更少具有随意性或受历史限制。相反，规范朝着最优个体或群体层面解决方案进化的空间更大。我们的研究结果还表明，诸如增加对公共物品贡献的合作规范可能需要进化出的道德偏好，而不仅仅是对偏离者的社会制裁，才能保持稳定。
