Kramer Karen L
Department of Anthropology, University of Utah, Salt Lake City, UT, 02138, USA,
Hum Nat. 2014 Mar;25(1):49-65. doi: 10.1007/s12110-013-9189-5.
The evolution of cooperative breeding is complex, and particularly so in humans because many other life history traits likely evolved at the same time. While cooperative childrearing is often presumed ancient, the transition from maternal self-reliance to dependence on allocare leaves no known empirical record. In this paper, an exploratory model is developed that incorporates probable evolutionary changes in birth intervals, juvenile dependence, and dispersal age to predict under what life history conditions mothers are unable to raise children without adult cooperation. The model's outcome variable (net balance) integrates dependent children's production and consumption as a function of varying life history parameters to estimate the investment mothers or others have to spend subsidizing children. Results suggest that maternal-juvenile cooperation can support the early transition toward a reduction in birth intervals, a longer period of juvenile dependence, and having overlapping young. The need for adult cooperation is most evident when birth intervals are short and age at net production is late. Findings suggest that the needs of juveniles would not have been an early selective force for adult cooperation. Rather, an age-graded division of labor and the mutual benefits of maternal-juvenile cooperation could be an important, but overlooked step in the evolution of cooperative breeding.
合作繁殖的演化过程十分复杂，在人类中更是如此，因为许多其他生活史特征可能是同时演化的。虽然合作育儿通常被认为由来已久，但从母亲自给自足到依赖他人照顾的转变却没有留下任何已知的实证记录。在本文中，我们构建了一个探索性模型，该模型纳入了生育间隔、幼年期依赖和扩散年龄等可能的进化变化，以预测在何种生活史条件下母亲在没有成年人合作的情况下无法抚养孩子。该模型的结果变量（净平衡）将依赖儿童的生产和消费整合为不同生活史参数的函数，以估计母亲或其他人补贴孩子所需的投入。结果表明，母婴合作能够支持向缩短生育间隔、延长幼年期依赖以及生育年龄重叠的早期转变。当生育间隔较短且净生产年龄较晚时，对成年人合作的需求最为明显。研究结果表明，幼年期的需求并非成年人合作的早期选择压力。相反，按年龄划分的劳动分工以及母婴合作的互利可能是合作繁殖演化过程中一个重要但被忽视的步骤。
