Miami Dade College Evolution as Fact and Theory Article Discussion for the attached file (evil as fact and theory) I need max 450 words about “The fact of

Miami Dade College Evolution as Fact and Theory Article Discussion 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 Gould’s writing on this?”for the other two attachments one is examples on how to write about the (Nunn sleep) attatchment 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.
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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
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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
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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…
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