What is it about?

Maternal resource availability and metabolism have a strong limiting effect on reproductive output in mammals. Since both non-maternal care (allocare) and domestication increase the energy available to the a breeding female, both are expected to correlate with an increase in reproductive output. Because domestication and different forms of allocare differ in terms of both in terms of reliability and quantity of energy provided, we can compare their effects to address fundamental questions about how resource availability and metabolism impose constraints on mothers. Our study is the largest comparative study of mammalian reproductive output (up to 1404 species, depending on specific data availability) encompassing both non-maternal care information and a large variety of reproduction variables representing reproductive output. The results of our study suggest that the increase in reproductive power seen in domesticated species may represent a physiological cap imposed by the requirement that all milk fed to an infant must first be metabolized by a lactating female. Allonursing species are able to bypass that cap by spreading the metabolic demands across multiple females.

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Why is it important?

Here we demonstrate that a naturally evolved behavior (allonursing) has greater effect on reproductive power than artificial selection and the large quantity of resources provided by domestication. In this, we demonstrate the importance of resource optimization afforded by sociality (rather than resource abundance per se) in shaping a species’ life history profile and its ability to overcome its own physiological constraints. These finding can have significant implications for the understanding of our own reproductive physiology, which is unique among primates as it is characterized by a very high reproductive power, and may have co-evolved with the practice of allonursing.


Working on this project has helped me realize the extent to which physiological and biological adaptations are inextricably liked to social ones. I think this has profound implications for our own evolution, and for the way we approach questions relating to it. Specifically, I think this work highlights the importance of multidisciplinary and comparative perspectives when addressing our evolutionary history.

paola cerrito
New York University

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This page is a summary of: A milk-sharing economy allows placental mammals to overcome their metabolic limits, Proceedings of the National Academy of Sciences, March 2022, Proceedings of the National Academy of Sciences,
DOI: 10.1073/pnas.2114674119.
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