Department of Anthropology, University of California, Santa Barbara, CA 93106.
Broom Center for Demography, University of California, Santa Barbara, CA 93106.
Proc Natl Acad Sci U S A. 2022 Jul 12;119(28):e2200073119. doi: 10.1073/pnas.2200073119. Epub 2022 Jul 6.
In classical evolutionary models, the force of natural selection diminishes with age toward zero by last reproduction. However, intergenerational resource transfers and other late-life contributions in social species may select for postreproductive longevity. We present a formal framework for estimating indirect fitness contributions via production transfers in a skills-intensive foraging niche, reflecting kinship and cooperation among group members. Among contemporary human hunter-gatherers and horticulturalists, indirect fitness contributions from transfers exceed direct reproductive contributions from before menopause until ages when surpluses end, around the modal age of adult death (∼70 y). Under reasonable assumptions, these benefits are the equivalent to having up to several more offspring after age 50. Despite early independence, minimal production surplus, and a shorter lifespan, chimpanzees could theoretically make indirect contributions if they adopted reliable food-sharing practices. Our results for chimpanzees hypothetically adopting hunter-gatherer subsistence suggest that a skills-intensive foraging ecology with late independence and late peak production could select for human-like life histories via positive feedback between longevity and late-life transfers. In contrast, life history changes preceding subsistence shifts would not favor further life extension or subsistence shifts. Our results formalize the theory that longevity can be favored under socioecological conditions characterized by parental and alloparental care funded through transfers of mid- to late-life production surpluses. We also extend our analysis beyond food transfers to illustrate the potential for indirect fitness contributions from pedagogy, or information transfers. While we focus mostly on humans, our approach is adaptable to any context or species where transfers can affect fitness.
在经典的进化模型中，自然选择的力量随着年龄的增长而逐渐减弱，最终在最后一次繁殖后趋近于零。然而，在社会性物种中，代际资源转移和其他晚年贡献可能会选择延长生殖后期的寿命。我们提出了一个正式的框架，用于估计通过技能密集型觅食生态位中的生产转移来间接适应度贡献，反映了群体成员之间的亲缘关系和合作。在当代人类狩猎采集者和园艺师中，从转移中获得的间接适应度贡献超过了绝经前的直接生殖贡献，直到盈余结束的年龄，大约是成年死亡的模态年龄（约 70 岁）。在合理的假设下，这些好处相当于在 50 岁以后再多生育几个孩子。尽管早期独立、生产盈余最小和寿命较短，如果黑猩猩采用可靠的食物分享实践，它们理论上可以做出间接贡献。我们对黑猩猩假设采用狩猎采集者生存方式的结果表明，如果采用技能密集型觅食生态位，具有晚期独立和晚期高峰生产的特点，那么通过长寿和晚期生活转移之间的正反馈，可能会选择出类似人类的生活史。相比之下，在生存方式转变之前的生活史变化不会有利于进一步延长寿命或生存方式转变。我们的结果使理论化，即在由转移中晚期生产盈余提供资金的父母和同代养育的社会生态条件下，长寿可以得到青睐。我们还将我们的分析扩展到食物转移之外，以说明从教育学或信息转移中获得间接适应度贡献的潜力。虽然我们主要关注人类，但我们的方法适用于任何可以通过转移影响适应度的背景或物种。
