Human children are frequently cared for by non-parental caregivers (alloparents), yet few studies have conducted systematic alternative hypothesis tests of why alloparents help. Here we explore whether predictions from kin selection, reciprocity, learning-to-mother and costly signalling hypotheses explain non-parental childcare among Agta hunter-gatherers from the Philippines. To test these hypotheses, we used high-resolution proximity data from 1,701 child–alloparent dyads. Our results indicated that reciprocity and relatedness were positively associated with the number of interactions with a child (our proxy for childcare). Need appeared more influential in close kin, suggesting indirect benefits, while reciprocity proved to be a stronger influence in non-kin, pointing to direct benefits. However, despite shared genes, close and distant kin interactions were also contingent on reciprocity. Compared with other apes, humans are unique in rapidly producing energetically demanding offspring. Our results suggest that the support that mothers require is met through support based on kinship and reciprocity.
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We thank the Human Evolutionary Ecology Group for comments on earlier drafts, our assistants in the Philippines, and most importantly, the Agta. We also thank L. Barrett, G. Bentley and R. Sear for guidance and useful suggestions to improve this work. This project was funded by Leverhulme Trust Grant RP2011-R 045 (to A.B.M. and R.M.). R.M. received funding from European Research Council Advanced Grant AdG 249347. A.E.P. received funding from the MRC and DFID (grant number MR/P014216/1). The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.
The authors declare no competing interests.
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Page, A.E., Thomas, M.G., Smith, D. et al. Testing adaptive hypotheses of alloparenting in Agta foragers. Nat Hum Behav 3, 1154–1163 (2019). https://doi.org/10.1038/s41562-019-0679-2
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