Rolf Degen summarizing: The emergence of the ability to build elevated sleeping nests allowed great apes to adopt a more comfortable & human-like sleep posture than the one monkeys take up

Nesting, sleeping, and nighttime behaviors in wild and captive great apes. James R. Anderson, Mabel Y. L. Ang, Louise C. Lock, Iris Weiche. Primates, Apr 10 2019. https://link.springer.com/article/10.1007/s10329-019-00723-2

Abstract: The past few decades have seen a burgeoning of scientific studies on great apes’ use of nests for sleeping in the wild, as well as their nesting behavior and sleep in captivity. We review recent advances in knowledge of these topics, with the aim of promoting information exchange between people working in the field and with captive great apes. We trace developments in research into nest-building techniques in adults and immatures, factors that influence selection of general sleeping sites and specific locations, social aspects of sleep, postures, and nighttime activities. We argue that exchanges of information deriving from studies of captive and wild apes are valuable for obtaining a better understanding of sleep-related adaptations in our nearest evolutionary neighbors, and conclude by making some recommendations regarding sleeping arrangements in captivity from a welfare perspective.

Keywords: Chimpanzee Bonobo Gorilla Orangutan Nest building Sleep posture Sleep quality Environmental enrichment Welfare