Activity around the clock: The evolution of sleep in human and non-human primates

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Sleep is a crucial aspect of primate life and my recent research has demonstrated how deeply connected sleep is to our species' evolutionary history and how it is associated with many trade-offs that are important to the success of modern humans. Sleep deprivation impairs some of the most important mental and physical attributes of our species: working memory, attention, visuomotor performance, and decision making. Yet, many of the most important jobs in modern society require high cognitive performance and mental acuity - all while coupled with low-quality sleep. For example, pilots, doctors, and police officers have round-the-clock duties, but limited opportunities to sleep. A central premise of our proposal is that many animals face sleep challenges due to ecological conditions, and evolution has optimized their responses to these challenges. Another premise is that we inherited sleep needs, including sleep-cognition constraints, from our primate ancestors. This proposal aims to provide a fundamentally new perspective on sleep-flexibility by investigating sleep in captive non-human primates, human hunter-gatherers and applying our findings to Western human sleep. I propose to apply modern phylogenetic and statistical methods to assess variation in sleep and will contribute to building a database on primate-sleep variation in relation to ecology and stress. Therefore, the aims of this proposal advance the field of Evolution and Ecology by generating and providing urgently needed primate sleep architecture data by integrating field, comparative, and theoretical projects under one research program that will ultimately transform our understanding of the evolution of primate sleep. Specifically, I will test the hypothesis that evolution has optimized primate responses to ecological challenges by selecting for species-specific flexibility of sleep duration, depth, and timing throughout a typical 24-hour day-night cycle. I will explore sleep in a trade-off framework (i.e., cost-benefit) by working towards three specific aims: (1) generating original sleep data in gibbons and gorillas and combine it with existing data on multiple human populations and non-human primates. (2) To assess whether humans are characterized by more flexible sleep, I will develop a theoretical model to generate null distributions of individual, group, and species-level sleep dynamics. (3) Finally, the proposed research will contribute to building a database on primate sleep variation that will transform our understanding of the evolution of primate sleep. As a primate lineage, humans are unique - in a remarkably short period of time we migrated and adapted to an array of habitats at a global scale. Therefore, it is critical to target traits, such as sleep, within a phylogenetic framework that contribute to the unique status and evolutionary success of our species relative to other primates.