Social support networks play a key role in human livelihood security, especially in vulnerable communities. Here we explore how evolutionary ideas of kin selection and intrahousehold resource competition can explain individual variation in daily support network size and composition in a south-central Ethiopian agricultural community. We consider both domestic and agricultural help across two generations with different wealth-transfer norms that yield different contexts for sibling competition. For farmers who inherited land rights from family, firstborns were more likely to report daily support from parents and to have larger nonparental kin networks (n = 180). Compared with other farmers, firstborns were also more likely to reciprocate their parents’ support, and to help nonparental kin without reciprocity. For farmers who received land rights from the government (n = 151), middle-born farmers reported more nonparental kin in their support networks compared with other farmers; nonreciprocal interactions were particularly common in both directions. This suggests a diversification of adult support networks to nonparental kin, possibly in response to a long-term parental investment disadvantage of being middle-born sons. In all instances, regardless of inheritance, lastborn farmers were the most disadvantaged in terms of kin support. Overall, we found that nonreciprocal interactions among farmers followed kin selection predictions. Direct reciprocity explained a substantial part of the support received from kin, suggesting the importance of the combined effects of kin selection and reciprocity for investment from kin.

中文翻译：

---

亲属选择理论是否有助于解释埃塞俄比亚中南部农民的支持网络？

社会支持网络在人类生计安全，特别是在脆弱社区中起着关键作用。在这里，我们探索亲属选择和家庭内部资源竞争的进化思想如何解释埃塞俄比亚中南部农业社区日常支持网络规模和组成的个体差异。我们认为两代人的家庭和农业帮助都具有不同的财富转移规范，这些规范为兄弟姐妹竞争提供了不同的环境。对于从家庭继承土地权利的农民来说，长子更有可能报告父母的日常支持并拥有更大的非父母亲属网络（n = 180）。与其他农民相比，长子也更可能回报父母的支持，并在没有互惠的情况下帮助非父母亲。对于从政府获得土地权利的农民（n = 151），与其他农民相比，中产农民在其支持网络中报告了更多的非父母亲。在两个方向上，不可逆的相互作用尤为普遍。这表明成人支持网络向非父母亲的多样化，这可能是对作为中年儿子的长期父母投资劣势的反应。在所有情况下，无论继承情况如何，就亲属支持而言，后代农民都是最弱势的群体。总体而言，我们发现农民之间的互惠互动遵循亲戚选择的预测。直接互惠解释了从亲戚那里获得的大部分支持，这表明亲戚选择和互惠相结合对亲戚投资的重要性。