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 transfers of food according to age, sex, kinship and the net 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.

代际间的资源转移是当前解释人类生命史进化（life-history evolution）的核心要素，该类模型能够阐释人类漫长的发育周期、延长的寿命以及绝经现象。将这类模型与汉密尔顿广义适合度（inclusive fitness）理论相结合，我们可预测：生物学亲缘关系与资源生产的年龄分布之间的相互作用，应是代际资源转移的关键驱动因素。针对玻利维亚亚马孙地区的齐曼内人（Tsimane'）觅食-园艺混合族群这一实证案例，我们详细刻画了食物净转移随年龄、性别、亲缘关系以及供体与受体的净需求变化的特征。研究显示，父母、祖父母与兄弟姐妹会在代际间产生显著的食物净向下转移。我们还证实，食物供给的程度会根据家庭生产力与人口结构的变化做出适应性调整，这与理论预测的结果一致。我们提出假说：提供这类关键资源转移的动机，是维系人类核心家庭与扩展家庭的根本性力量。人类社会中三代同堂家庭的普遍存在，或许直接反映了生命体在生命史与社会组织层面所受到的根本性进化约束。