Title: High-resolution maps of hunter-gatherer social networks reveal human adaptation for cultural exchange

Are interactions with unrelated and even unknown individuals a by-product of modern life in megacities? Here we argue instead that social ties among non-kin are a crucial human adaptation. By deploying a new portable wireless sensing technology (motes), we mapped social networks in Agta and BaYaka hunter-gatherers in unprecedented detail. We show that strong friendships with non-kin optimize the global efficiency of their social networks thereby facilitating cultural exchange, and that the adaptation for forming friendship ties appears early in development. The ability to extend networks and form strong non-kin ties may explain some human distinctive characteristics such as hypersociality and cumulative culture, and the tendency to exchange ideas with unrelated and unknown individuals in megacities and online social networks. One Sentence Summary: Social networks of two hunter-gatherer groups in Congo and the Philippines reveal that friendships are an ancestral adaptation for the exchange of information and culture. not peer-reviewed) is the author/funder. All rights reserved. No reuse allowed without permission. The copyright holder for this preprint (which was . http://dx.doi.org/10.1101/040154 doi: bioRxiv preprint first posted online Feb. 19, 2016;