Fluent Essays

for the attached file (evil as fact and theory) I need max 450 words about The fact of evolution is that life in the past was different than it is today. The theory of evolution is the explanation for why life has changed. What did you think of Goulds writing on this?for the other two attachments one is examples on how to write about the (Nunn sleep) attatchment nunn_sleep.pdf exemplary_responses.docx evolution_as_fact_and_theory.docx Unformatted Attachment Preview 227 review Evolution, Medicine, and Public Health [2016] pp. 227–243 doi:10.1093/emph/eow018 Shining evolutionary light on human sleep and sleep disorders Charles L. Nunn*,1,2,3, David R. Samson1 and Andrew D. Krystal4 1 Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA; 2Duke Global Health Institute, Durham, North Carolina 27710, USA; 3Triangle Center for Evolutionary Medicine, Durham, NC 27708, USA and 4Department of Psychiatry and Behavioral Sciences, Duke University School of Medicine, Durham, NC 27710 *Correspondence address. Department of Evolutionary Anthropology, Duke University, Durham, North Carolina 27708, USA; Tel: 919 660 7281; E-mail:clnunn@duke.edu Received 25 March 2016; revised version accepted 15 June 2016 ABSTRACT Sleep is essential to cognitive function and health in humans, yet the ultimate reasons for sleep—i.e. ‘why’ sleep evolved—remain mysterious. We integrate findings from human sleep studies, the ethnographic record, and the ecology and evolution of mammalian sleep to better understand sleep along the human lineage and in the modern world. Compared to other primates, sleep in great apes has undergone substantial evolutionary change, with all great apes building a sleeping platform or ‘nest’. Further evolutionary change characterizes human sleep, with humans having the shortest sleep duration, yet the highest proportion of rapid eye movement sleep among primates. These changes likely reflect that our ancestors experienced fitness benefits from being active for a greater portion of the 24-h cycle than other primates, potentially related to advantages arising from learning, socializing and defending against predators and hostile conspecifics. Perspectives from evolutionary medicine have implications for understanding sleep disorders; we consider these perspectives in the context of insomnia, narcolepsy, seasonal affective disorder, circadian rhythm disorders and sleep apnea. We also identify how human sleep today differs from sleep through most of human evolution, and the implications of these changes for global health and health disparities. More generally, our review highlights the importance of phylogenetic comparisons in understanding human health, including well-known links between sleep, cognitive performance and health in humans. K E Y W O R D S : sleep disorder; evolutionary mismatch; comparative study; phylogeny; human health; human evolution. INTRODUCTION Sleep is essential to cognitive function and health in humans. For example, experiments have shown that sleep is important for working memory, attention, decision-making, and visual-motor performance [1– 3]. Chronic sleep deprivation and alterations in circadian rhythms, such as shift work, also increase the risks for obesity, hypertension, heart disease and ß The Author(s) 2016. Published by Oxford University Press on behalf of the Foundation for Evolution, Medicine, and Public Health. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. 228 | Nunn et al. Evolution, Medicine, and Public Health immune system dysfunction, which may increase the risks for infection, inflammation, and some types of cancer [4–8]. In the USA, 50–70 million Americans suffer from chronic sleep disorders, and 20\% of serious automobile accidents are attributable to sleep deprivation [9]. Although less is known about global variation in sleep patterns [10], rates of sleep problems and chronic sleep deprivation are probably increasing in developing countries, where aging populations, transitions to market economies, and adoption of Western lifestyles are altering sleep patterns [11–13]. Despite growing appreciation of the importance of sleep, the ultimate reasons for sleep remain mysterious. Sleep appears to help rejuvenate the brain, including purging byproducts of metabolism that accumulate during the day [14]. The growing realization that sleep interconnects deeply with many other physiological and cognitive mechanisms suggests that sleep has many functions, including growth and repair of the body (e.g. release of growth hormone, 15), immune function [16, 17], and even adaptive stillness to avoid predation [18, 19]. These functions are likely to vary in importance across species, including in humans compared to other primates. In addition, evolutionary perspectives involving tradeoffs are important for understanding sleep, including tradeoffs between sleep and other fitness relevant activities such as foraging or caring for offspring, and also pleiotropic effects of genes on sleep and related physiological processes. We need to understand why humans sleep the way we do, why sleep deprivation is so detrimental to our health through various neurological and physiological mechanisms, and how we can sleep better. Here, we integrate recent findings from human sleep studies and the ecology and evolution of sleep, with the goal to deepen our understanding of human sleep, including sleep disorders and the global health implications of sleep deficiency. A central premise of our article is that human sleep has undergone changes from our primate ancestors [20, 21]. These derived characteristics (and their correlates) may hold important clues to understanding the links between sleep, cognitive performance and human health. Another premise is that humans in the developed world sleep differently than our ancestors did [21, 22]. These changes partly arise through increased access to electrical lighting in the developed world, but also through our use of separate bedrooms, soft beds and cultural norms against daytime napping. A final premise is that evolutionary concepts, such as tradeoffs, are important for understanding human sleep. We begin by considering patterns of human sleep in relation to other primates, including the ways that human sleep differs from our close evolutionary relatives. We also review recent hypotheses involving sleep and infants [23, 24]. In an effort to understand the reasons why human sleep differs from other primates, we review our knowledge of sleep patterns across mammals, focusing on the correlates of that variation. We also provide evolutionary perspectives on several major sleep disorders, and on links between poor or disrupted sleep and health disparities. We suggest that sleep deprivation is a largely unrecognized global health problem that may contribute to both infectious and non-infectious disease risks in developing countries, and to health disparities in developed countries. HUMAN SLEEP IN PRIMATE PERSPECTIVE Most primate species are arboreal, and this appears to be the ancestral state for primates [25]. Kappeler [26] used primate life history traits to reconstruct the evolutionary history of sleep site usage. His analysis revealed that the ancestral primate probably resembled extant galagos: they were likely to be nocturnal, solitary and producing a single offspring that was provisioned in a tree-hole nest, or ‘fixed-point’ sleep site. A primary advantage of these fixed-point sleep sites may have been increased safety from predators [27], along with improved thermoregulation [28]. Like many other mammals, the primate lineages emanating from the Paleocene evolved increased body size [29, 30]. This increase in body size led primates on many of these lineages to abandon fixedpoint sleep sites, as naturally occurring enclosed sites would be challenging for larger animals to find. Similarly, the evolution of diurnal activity patterns— and associated shifts to living in larger groups [31]— would have made it even more difficult for larger groups of animals to locate fixed point sleep sites. These factors led early primates to abandon the advantages of enclosed and sturdy sleep sites, and to instead sleep on tree branches. Sleeping on branches would have exposed these animals to increased risks from predation and to falling, especially because wind speeds, with punctuated gusts, are greater in the canopy [32]. Indeed, the primatology literature provides multiple accounts of Nunn et al. | Shining evolutionary light on human sleep primates falling from arboreal sleeping sites, resulting in injuries and death [33, 34]. Great ape sleep A major evolutionary transition in sleep likely occurred in the ancestor of the great apes: humans, orangutans, gorillas, chimpanzees and bonobos all build platforms (or ‘nests’) upon which to sleep [35–37]. Great ape sleeping platforms show a conserved pattern of construction and function, and phylogenetic reconstruction points to emergence of this sleeping behavior sometime between 18 and 14 million years ago [38]. Typically, these platforms are built in trees that are selected for their firm, stable and resilient biomechanical properties [39–41]. Platforms are rebuilt each night, with each individual (except dependent young) building a separate sleeping nest. In sharp contrast, the lesser apes—the gibbons—do not build nests for sleeping. Instead, gibbons follow the pattern found in most monkeys: they typically sleep on branches in a lying or sitting position, with no environmental alterations [42, 43]. Why do great apes build sleeping platforms? Based on evidence showing a link between sleep and cognition in humans and great apes, the ‘sleep quality hypothesis’ proposes that more stable sleeping sites provide physical support needed for large bodied hominoids to maintain deep, sustained sleep to enable enhanced cognitive function [37, 44, 45]. An alternative ‘engineering hypothesis’ states that great ape platform building simply reflects greater cognitive ability, which enables the great apes to build nests [44]. This is a simple reversal of cause and effect, where the cause is greater cognitive facility providing the opportunity to build effective sleep platforms, rather than use of platforms to enable greater cognitive performance. Recent captive research on apes has tested two crucial elements of the sleep quality hypothesis for the use of sleeping platforms in great apes. In a zoo study, Samson and Shumaker [46] provided orangutans with varied sleep materials, and then scored the quality of sleeping platforms the orangutans produced with different materials. They found that sleeping platform quality was positively correlated with reduced arousability and lower sleep fragmentation (i.e. metrics of better quality sleep). In another study of zoo animals, Martin-Ordas and Call [47] found that, by making memory more resistance to the detrimental effects of interfering (i.e. distracting) activities, sleep plays a role in memory consolidation in chimpanzees, bonobos and orangutans. Increased body mass likely also played a role in the origins of great ape sleeping platforms [21]. In particular, larger-bodied great apes would find it more difficult to sleep on tree branches. This effect would have favored individuals that built more resilient sleeping platforms to reduce the probability of lethal falls, and to reduce physical stressors on the bodies of sleeping individuals. A distinct mass threshold (30 kg) has been proposed that separates the great apes that use sleeping platforms from the lesser apes and monkeys that do not [21, 45]. Once the use of sleeping platforms evolved, this could have enabled higher quality sleep within great apes, with emergent cognitive benefits. Human sleep Human sleep has undergone additional changes from other great apes in several key features. An obvious feature is where we sleep, namely on the ground; among other apes, terrestrial sleep is rare, occurring only when predation risk is low, and typically only by very large bodied males [48–51]. In contrast, humans of both sexes habitually sleep on the ground, which could plausibly provide even more stable sleeping locations to achieve even deeper sleep. Predation represents a major tradeoff in this context, with risk of predator attack thought to increase for terrestrial primates [52, 53]. In relation to human ground sleep, Coolidge and Wynn [54] proposed the ‘tree-to-ground hypothesis’. They suggested that when hominins became fully terrestrial they gained the advantage of greater stability than was possible in arboreal sleep. Freed from the disadvantages of arboreal sleep they could have achieved longer duration and higher quality sleep, which would have improved waking cognition. Without terrestrial sleeping sites, they argue, fully human procedural memory consolidation for visual-motor skills and visual-spatial locations could not have evolved. In addition, under the assumption that sleep plays a role in problem solving in social and other domains involving ‘threat simulation’ [55], they proposed that hominins would have been less primed for daily activity due to less sleep the previous night [20, 54]. The controlled use of fire may have been an essential precursor to secure ground sleep [20]. Arboreal sleeping platforms reduce predation risk [56] and 229 230 | Nunn et al. Evolution, Medicine, and Public Health minimize insect biting rates by masking host attractants or actually repelling insects [57, 58]. Sleeping platforms also provide some insulation for warmth [57], and give a stable and secure environment to enable higher quality sleep [39, 40]. A fire probably also reduces risk of predation and provides opportunities for thermoregulation, while smoke reduces insect activity [59, 60]. Control of fire in early Homo erectus may therefore have enabled the nighttime transition from trees to the ground [20, 61]. Quantitative characteristics of human sleep have also evolved along the human lineage. We consider here two major aspects: reduced total sleep and a higher percentage of rapid eye movement (REM) sleep [21]. Humans are empirically the shortest sleeping primates and have the highest percentage of REM (Fig. 1). New phylogenetic methods can rigorously investigate evolutionary change on a single branch, allowing a comparative biologist to investigate whether an exceptional amount of evolutionary change has occurred [62, 63]. More specifically, these methods compare actual sleep characteristics in humans to the predicted outcomes from a statistical model that includes both phylogeny and a set of predictor variables that influence sleep characteristics. One can then test whether humans are a typical primate (our observed sleep duration falls within the predicted 95\% credible interval) or a ‘phylogenetic outlier’ (our sleep duration falls outside the predicted 95\% credible interval). Using this approach, Samson and Nunn [21] discovered that human sleep duration is extremely different from phylogenetic predictions: our actual sleep duration falls outside the 95\% credible interval, suggesting that we can be more than 95\% certain that human sleep differs from other primates. As we discuss below when considering the potential evolutionary drivers of shorter sleep along the human lineage, tradeoffs between sleep and other activities are likely to be important factors. When this same approach was applied to study the proportion of REM sleep in humans, the analyses revealed that humans pack a higher proportion of REM into their sleep than any other primate. It is worth noting, however, that some other primates have a longer absolute duration of REM sleep (see Fig. 1). As a last point of comparison to other primates, humans may be more flexible in the timing of sleep than our closest living relatives. Evidence from small-scale societies and subtropical hunter-gatherers [22], the historical record [64] and experiments in developed countries [65] suggest that humans show flexibility in their sleep. In a review of human sleep across cultures, Worthman [22] noted that, ‘Human nights are filled with activity and significance, and nowhere do people typically sleep from evening to dawn’ (p. 301). Similarly, reflecting on his study of the Pirahã hunter-gatherers in South America, Everett (66) noted, ‘Pirahãs take naps (fifteen minutes to two hours at the extremes) during the day and night. There is loud talking in the village all night long’ (p. 79). Similar patterns appeared to occur in European and equatorial societies prior to the advent of cheap and effective lighting, with a historical analysis documenting extensive use of the concept of ‘first sleep’ and ‘second sleep’, consistent with a biphasic sleep pattern that differs radically from what we consider ‘normal’ in Western societies today [64, 67]. Flexibility can also occur in the context of daytime sleep, i.e. the occurrence of napping or siestas. For example, Pennsylvanian Old Order Amish, a conservative Christian sect that avoids modern electrical conveniences, have been characterized as ‘common’ nap-takers, with 58\% of the population recording a nap a least once per week [68]. Counter to these findings and suggestions, however, a recent study of sleep in three hunter-gatherer populations [69] interpreted their actigraphy data as indicating consolidated sleep at night and with little napping during the day, and thus arguing against the flexibility of sleep. This presents a challenge, and calls for better methods of assessing sleep phasing using actigraphy, including through use of new algorithms, validation with reported episodes of sleep and wakefulness, and development of new methods to better assess sleep without reliance on actigraphy. It should be noted, however, that this study also revealed considerable heterogeneity in sleep onset time (but less in awakening), consistent with flexibility in the timing of sleep. Given the global distribution of humans, adaptation to local conditions may be expected for sleep, as seen for other human phenotypes. One obvious aspect of this involves latitude, and the effects of large changes in day-length throughout the year. Unfortunately, however, sleep research in circumpolar environments has primarily focused on European populations [70, 71] and the effects of latitude on the physiology of military personnel [72]. Thus, little is known regarding the effects of seasonally variable day–night cycles on the sleep-wake patterns of nonindustrial indigenous populations [12]. Moreover, reports of sleep in Nunn et al. | Shining evolutionary light on human sleep 231 Figure 1. Duration of REM, NREM and total sleep in primates. Humans sleep the least compared to all other primates, yet have the greatest proportion of total sleep time dedicated to REM Figure 2. Infant versus adult sleep. A sleep comparison between polyphasic human infant and consolidated sleep in an adult living in a post-industrial society (adapted from reference [75]) post-industrial societies have shown conflicting evidence and small effects with respect to sleep duration across seasons [73, 74]. Several factors may influence the outcome of such studies, including lack of direct exposure to changes in light and temperature among participants in laboratory environments, or the environmental buffer provided by modern work and residential facilities. In contrast, evidence supports the idea that sleep is modulated by season in traditional, equatorial societies; e.g. longer total sleep times (53–56 min increase) were associated with the ‘winter’ season in the San and Tsimane [69]. Sleep and human development Ontogeny can also shed light on human sleep. As all parents know, babies sleep a lot, yet they are born without a regular sleeping rhythm (Fig. 2). The chaos of sleep phasing in the first days of life consolidates into a polyphasic sleep schedule consisting of at first two naps and one bout of night-time sleep, and eventually one and then no naps (with longer consolidated sleep at n ... Purchase answer to see full attachment