Data from: Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society

Transfers of resources between generations are an essential element in current models of human life history evolution accounting for prolonged development, extended lifespan, and menopause. Integrating these models with Hamilton's theory of inclusive fitness, we predict that the interaction of biological kinship with the age-schedule of resource production should be a key driver of intergenerational transfers. In the empirical case of Tsimane' forager-horticulturalists in Bolivian Amazonia, we provide a detailed characterization of net food transfers according to age, sex, kinship, and the need of donors and recipients. We show that parents, grandparents, and siblings provide significant net downward transfers of food across generations. We demonstrate that the extent of provisioning responds facultatively to variation in the productivity and demographic composition of families, as predicted by the theory. We hypothesize that the motivation to provide these critical transfers is a fundamental force that binds together human nuclear and extended families. The ubiquity of three-generational families in human societies may thus be a direct reflection of fundamental evolutionary constraints on an organism's life history and social organization.

代际资源转移是当前解释人类生命史演化（涵盖发育周期延长、寿命延长与绝经现象）的各类模型中的核心要素。将此类模型与汉密尔顿广义适合度理论（Hamilton's theory of inclusive fitness）相结合后，我们推测：生物亲缘关系与资源生产的年龄节律之间的相互作用，应是驱动代际资源转移的关键因素。针对玻利维亚亚马逊地区提斯曼（Tsimane'）狩猎采集-园艺农耕族群这一实证案例，我们基于年龄、性别、亲缘关系以及供需双方的需求，对食物净转移模式进行了细致的特征刻画。研究显示，父母、祖父母与兄弟姐妹会在代际间实现显著的食物净向下转移（即资源由年长个体流向年轻个体）。我们证实，食物供给的规模会根据家庭生产能力与人口结构的变化做出灵活响应，这与理论的预测相符。我们提出假说：开展此类关键资源转移的动机，是维系人类核心家庭与扩大家庭的核心力量。因此，人类社会中三代同堂家庭的普遍存在，或许直接反映了生物体生命史与社会组织所受的根本性演化约束。