Maybe check the references in this article? https://theconversation.com/did-we-used-to-have-two-sleeps-rather-than-one-should-we-again-57806 https://theconvers

Maybe check the references in this article? https://theconversation.com/did-we-used-to-have-two-sleeps-rather-than-one-should-we-again-57806 https://theconversation.com/did-we-used-to-have-two-sleeps-r...