Maybe you are referring to David Samson's study of the Hadza tribe in Northern Tanzania? "Chronotype Variation Drives Nighttime Sentinel-Like Behaviour in Hunte

Maybe you are referring to David Samson's study of the Hadza tribe in Northern Tanzania? "Chronotype Variation Drives Nighttime Sentinel-Like Behaviour in Hunter-Gatherers", 2017. [0] Or in some more entertaining format at Duke University's website [1]. [0] http://dx.doi.org/10.1098/rspb.2017.0967 http://dx.doi.org/10.1098/rspb.2017.0967. [1] https://today.duke.edu/2017/07/live-grandparents-helped-human-ancestors-get-safer-night%E2%80%99s-sleep https://today.duke.edu/2017/07/live-grandparents-helped-huma...