IntroductionThe positive effects of physical activity (PA) on sleep are widely promoted by public health organizations and supported by abundant empirical evidence. Nonetheless, there remains a dearth of studies investigating the association between daytime PA and nighttime sleep among non-urban and nonindustrial populations that habitually engage in PA as part of their subsistence strategy.MethodsHere, we examined the bidirectional relationship between PA and sleep. We also looked at age, gender, and occupation-level differences in moderate-to-vigorous-intensity PA (MVPA), low-intensity PA (LPA), and sedentary activity durations among Basotho and Xhoxa agropastoralists residing in rural villages in the Eastern Cape, South Africa. We analyzed activity and sleep data collected from 113 individuals using MotionWatch actigraphy wristwatches across three field seasons (7111 individual days).ResultsPercentage daily total MVPA decreased with age, though older participants maintained low activity levels and did not suffer from poorer sleep compared to younger participants. Herders spent more percentage of their day in higher-intensity activity than non-herders. Overall, women had greater daily percentage MVPA and lower percentage sedentary activity than men. Durations of total MVPA and LPA decreased total sleep time (TST) and improved sleep quality (increased sleep efficiency (SE), decreased fragmentation, and decreased percentage wake after sleep onset). Daytime PA measures were not affected by sleep duration or quality from the previous night.ConclusionsAmong this group of habitually active agropastoralists, low-to-moderate-intensity PA durations consistently predicted higher sleep quality. Our findings showed that sleep quality was more strongly affected by PA than sleep duration.

Sleep is a vital physiological process that lab-based studies of model species, including humans, have shown is homeostatically regulated-i.e., pressure to sleep builds during wakefulness and dissipates during sleep. However, how wild animals maintain sleep homeostasis and how socio-ecological pressures interfere with their sleep remain understudied. Here, we investigated sleep homeostasis and the factors that influence sleep duration among wild Sumatran orangutans (Pongo abelii), leveraging a comprehensive long-term dataset of their behavior, sociality, and ecology. We quantified sleep in 53 adult individuals using the time that an individual spent in a sleeping nest-i.e., its sleep period-as an indicator of time spent sleeping. We found that, after shorter nighttime sleep periods, orangutans' next-day cumulative nap period duration was longer and that shorter nap periods were associated with a higher number of naps on the same day. We also found that orangutans had shorter sleep periods (night and day) when they associated with more conspecifics. Orangutans also had shorter nighttime sleep periods when they traveled farther the day before, and they had longer cumulative nap periods on days when (1) they ate fewer calories, (2) the ambient temperature was cooler, and (3) it rained. Our results suggest that multiple factors shape wild orangutans' sleep behavior and that orangutans compensate for lost sleep via daytime napping. This supports the hypothesis that social and ecological pressures interfere with sleep among wild animals and that they must balance the costs and benefits of sleep with those of other critical activities.

Interbreeding between modern humans and archaic hominins, including Neanderthals and Denisovans, occurred as modern humans migrated outside of Africa. Here, we report on evidence of adaptive introgression from archaic hominins within genomic regions associated with circadian rhythm cycling, chronotype, and sleep using 76 worldwide modern human populations from the Human Genome Diversity Project and 1000 Genomes Project. We identified 265 independent segments suggestive of adaptive introgression, where 22 of these segments show evidence of positive selection. We tested for evidence of a latitudinal cline within 35 core haplotypes, finding no clear latitude gradient, and identified the likely archaic donor for each of these haplotypes. We found that several genes with evidence of adaptive introgression are associated with affective disorders, chronotype, and respiratory diseases. Lastly, many of the variants are eQTLs for several genes that are significantly enriched in immunity pathways.

This study investigates the "First Settler Wellness Effect," exploring how cultural geography impacts traditional wellness (physical health, social relationships, and financial stability) and existential wellness (purpose, meaning, and community identity) across the United States. Using data from the Gallup-Healthways Well-Being Index, which includes responses from over 325,000 individuals across 110 Metropolitan Statistical Areas (MSAs) from 2009 to 2016, we analyze wellness outcomes through the lens of the American Nations Model. This model categorizes the United States into distinct cultural regions shaped by early settlement patterns, emphasizing the enduring influence of regional norms and ideologies. Our findings, in support of the American Nations Model, reveal significant regional variation in wellness outcomes. Northeastern and Midwestern regions, characterized by communal norms, high educational attainment, and institutional trust, exhibit elevated traditional wellness scores (e.g., β = 0.371, p = 0.002). These regions reflect a stability rooted in health infrastructure and economic security. In contrast, Southern regions, shaped by honor-based values emphasizing personal autonomy, loyalty, and social reputation, show significantly higher existential wellness (e.g., β = 0.590, p = 0.011). This divergence highlights a tradeoff between material stability and existential fulfillment shaped by cultural norms. Interestingly, Southern regions demonstrate elevated existential wellness for Black and Hispanic residents compared to other regions, suggesting localized cultural or community support may offset systemic disparities. Conversely, Northeastern and Midwestern regions report higher traditional wellness yet fail to foster similar levels of existential fulfillment, underscoring the limitations of material prosperity alone. These findings emphasize the interplay between cultural history, regional identity, and human flourishing, offering insights for targeted public health and policy interventions.

OBJECTIVES:To examine seasonal sleep variation and assess the effects of gender, age, and environmental variables (Wet-Bulb Globe Temperature, moonlight, sunrise and sunset times) on sleep in a rural agropastoral community in South Africa with gender division of labor. METHODS:We collected actigraphy data from 114 participants (83 men, 31 women, 4750 nights) during summer and winter seasons in 2023. We used Bayesian hierarchical regression models to investigate drivers of sleep duration and quality. RESULTS:Total Sleep Time was longer in winter (7.26 hours, SD = 1.0) compared to summer (6.40 hours, SD = 0.88), but so were Fragmentation Index and Wake After Sleep Onset. Higher Wet-Bulb Globe Temperature was associated with shorter Total Sleep Time, higher Fragmentation Index, and lower Sleep Efficiency. Greater moon illumination was correlated with shorter Total Sleep Time and reduced Fragmentation Index and Wake After Sleep Onset. Age was positively correlated with Total Sleep Time and Fragmentation Index among men, and older individuals had earlier sleep onset and offset than younger individuals. Compared to women, men had shorter and more disturbed sleep, especially in the winter, and were more impacted by Wet-Bulb Globe Temperature. CONCLUSIONS:Sleep during the winter season was longer but more fragmented and of lower quality compared to the summer. Seasonal differences in extrinsic weather conditions and perceived risks operated on preexisting gendered labor and sleep disparities to drive seasonal sleep variation in this community. Future research should consider the disproportionate effects that environmental variables can have on sleep outcomes for different groups.

Sleep is subject to Darwinian fitness and thereby constrained by ecological and social factors. Nevertheless, most comparative research on sleep is conducted in laboratory settings, detached from environmental and social influences, which is problematic for evolutionary theories. We examined the natural sleeping patterns of wild chimpanzees in Budongo Forest, Uganda, using a remote-controlled, infrared camera system. We found that sleep in chimpanzees was significantly affected by social factors, including the sleeper’s own rank and the composition of the nearby sleeping party. Nesting in groups increased sleep duration and decreased sleep fragmentation compared with sleeping alone, despite the fact that it delayed nesting times and advanced wake times. Rank had little impact on female sleep but a strong influence on male sleep, with high-ranking males generally experiencing shorter and more fragmented sleep compared with subordinate males. The presence of sexually active females also reduced sleep duration, by delaying nest building, advancing wake time, and increasing sleep fragmentation. Our data show that natural sleep patterns in chimpanzees are largely determined by social variables that continue to exert their influence into the night. We discuss the implications of studying sleep patterns of our closest relatives in ecologically and socially valid situations for future research on the evolution of sleep.

While most studies on Daylight Saving Time (DST) focus on human sleep and well-being, there is a dearth of understanding of how this sudden, human-mitigated change affects the routines of companion animals. The objective of this study was to assess how DST influenced the morning activity pattern of dogs (Canis familiaris). We used accelerometers to record activity in 25 sled dogs and 29 caregiver-companion dog dyads located in or near Ontario, Canada during the Fall Back time shift. We looked at morning onset activity based on sunrise time (both groups), handler arrival time (sled dogs), and caregiver Got-up Time (companion dogs), and compared pre-DST measures with the three days following DST. We found that sled dogs were less active around sunrise in all post-DST days compared to pre-DST, as sunrise coincided with handler arrival time before DST but not after. Companion dogs showed no change in morning activity based on sunrise times before and after DST. On the Sunday of DST, sled dogs were more active before handlers arrived, but their activity returned to pre-DST levels in the following two days. Caregiver and companion dog activities did not change on the day of DST. After DST, caregivers woke up earlier on weekdays, but companion dogs maintained their pre-DST activity patterns. Overall, we found that sled dogs took one day to adjust to a change in handler arrival time yet neither companion dogs nor their caregivers showed any morning activity difference after the Fall Back DST transition. In summary, our findings highlight the importance of flexible routines and gradual changes in helping dogs adjust to abrupt schedule modifications, offering valuable insights for optimizing dog care practices during time shifts.

Background: Sleep deprivation is a critical risk factor for physical and mental health problems. The current study examined whether sleep problems were related to housing status and physical and mental health among people experiencing homelessness. Methods: Data were collected via an anonymous survey completed by adults accessing services at a day shelter in Oklahoma City, OK. Demographic characteristics, sleep problems, days of poor physical and mental health, and self-rated health were assessed and compared across housing subgroups. Logistic regression analyses were performed to examine potential associations between sleep and health. Results: Participants (N = 404) were predominantly male (71.0%) and racially minoritized (57.4%) with an average age of 47.0 (SD = 11.6) years. Days of unintentional sleep over the past 30 days differed significantly by housing status. Logistic regression analyses indicated that short sleep duration of <= 6 hours was associated with poorer self-rated health and more days of poor physical health over the past 30 days compared to those who reported an optimal sleep duration of 7-9 hours. Additionally, reporting >= 1 day of unintentional daytime sleep was associated with more days of poor mental and physical health over the past 30-day. Reporting more days of inadequate sleep was associated with poorer self-rated health, and more days of poor physical and mental health over the past 30 days. Conclusion: Sleep problems were associated with poorer physical and mental health among people experiencing homelessness. Safe environments where adults experiencing homelessness can sleep comfortably and without interruption may be needed to support good physical and mental health. (c) 2023 National Sleep Foundation. Published by Elsevier Inc. All rights reserved.

Interbreeding between modern humans and archaic hominins, including Neanderthals and Denisovans, occurred as modern humans migrated outside of Africa. Here, we report on evidence of introgression from archaic hominins within genomic regions associated with circadian rhythm and chronotype using 76 worldwide modern human populations from the Human Genome Diversity Project and 1000 Genomes Project. We calculated the extent of regions indicative of adaptive introgression across the autosomes and identified regions that are suggested to be under positive selection. We tested for evidence of a latitudinal cline within 36 core haplotypes along with presenting the likely archaic donor for each of these haplotypes. We identified 265 independent segments that overlap genes described as having a circadian rhythm component or contain variants and segments previously identified as being associated with circadian rhythm or chronotype. Within these segments we found 1,729 archaically derived variants with allele frequencies of at least 40% intersecting 303 genes and intergenic segments. Seventeen of these segments show evidence of positive selection, three of which are found within our core haplotypes. We found that many of our genes are associated with the immune system or gastrointestinal function. Additionally, variants associated with complex traits such as schizophrenia and bipolar disorder are present within our adaptively introgressed regions. Lastly, genes and markers associated with sleep and chronotype phenotypes and serotonin pathways were also found in our adaptive introgression results, potentially signalling selection on genes related to seasonal light variation as modern humans migrated into new environments after leaving Africa. ### Competing Interest Statement The authors have declared no competing interest.

The function of dreams is a longstanding scientific research question. Simulation theories of dream function, which are based on the premise that dreams represent evolutionary past selective pressures and fitness improvement through modified states of consciousness, have yet to be tested in cross-cultural populations that include small-scale forager societies. Here, we analyze dream content with cross-cultural comparisons between the BaYaka (Rep. of Congo) and Hadza (Tanzania) foraging groups and Global North populations, to test the hypothesis that dreams in forager groups serve a more effective emotion regulation function due to their strong social norms and high interpersonal support. Using a linear mixed effects model we analyzed 896 dreams from 234 individuals across these populations, recorded using dream diaries. Dream texts were processed into four psychosocial constructs using the Linguistic Inquiry and Word Count (LIWC-22) dictionary. The BaYaka displayed greater community-oriented dream content. Both the BaYaka and Hadza exhibited heightened threat dream content, while, at the same time, the Hadza demonstrated low negative emotions in their dreams. The Global North Nightmare Disorder group had increased negative emotion content, and the Canadian student sample during the COVID-19 pandemic displayed the highest anxiety dream content. In conclusion, this study supports the notion that dreams in non-clinical populations can effectively regulate emotions by linking potential threats with non-fearful contexts, reducing anxiety and negative emotions through emotional release or catharsis. Overall, this work contributes to our understanding of the evolutionary significance of this altered state of consciousness.

Evolutionary theories suggest that dreams function as a world simulator of events that maximizes our ability to surmount social and threat-related challenges critical to survivorship and reproduction. Here, in contrast to the incorporation continuity hypothesis, we test the (1) social bias hypothesis, which states that dreams will overrepresent positive social interactions relative to waking life, (2) the mutually exclusive threat bias hypothesis, the idea that dream content will be negative relative to waking life, (3) the strengthening hypothesis, which states that dreams will rehearse more positive interactions with individuals the self is familiar with relative to waking life, and (4) the compensation hypothesis, which states that social contents in dreams increases during periods of social seclusion. Dream (n = 168) and wake (n = 184) reports were collected through a standardized online survey from 24 undergraduate students. Recalls were analyzed using the Social Content Scale. Generalized linear mixed effects models were used, and the following fixed-effects were considered for the study; the number of reports contributed, report state, biological sex, stress, social support, and media exposures. Results showed support for the threat bias hypothesis, we found that dreams were more negative and featured more unfamiliar individuals in contrast to waking life. Additionally, we found partial support for the social bias and the strengthening hypotheses, however no support was shown for the compensation hypothesis. Overall, these results demonstrate support for the threat simulation function of dreams.

Abstract Background and objectives Sleep is a vulnerable state in which individuals are more susceptible to threat, which may have led to evolved mechanisms for increasing safety. The sentinel hypothesis proposes that brief awakenings during sleep may be a strategy for detecting and responding to environmental threats. Observations of sleep segmentation and group sentinelization in hunter-gatherer and small-scale communities support this hypothesis, but to date it has not been tested in comparisons with industrial populations characterized by more secure sleep environments. Methodology Here, we compare wake after sleep onset (WASO), a quantitative measure of nighttime awakenings, between two nonindustrial and two industrial populations: Hadza hunter-gatherers (n = 33), Malagasy small-scale agriculturalists (n = 38), and Hispanic (n = 1,531) and non-Hispanic White (NHW) (n = 347) Americans. We compared nighttime awakenings between these groups using actigraphically-measured sleep data. We fit linear models to assess whether WASO varies across groups, controlling for sex and age. Results We found that WASO varies significantly by group membership and is highest in Hadza (2.44 h) and Malagasy (1.93 h) and lowest in non-Hispanic Whites (0.69 h). Hispanics demonstrate intermediate WASO (0.86 h), which is significantly more than NHW participants. After performing supplementary analysis within the Hispanic sample, we found that WASO is significantly and positively associated with increased perception of neighborhood violence. Conclusions and implications Consistent with principles central to evolutionary medicine, we propose that evolved mechanisms to increase vigilance during sleep may now be mismatched with relatively safer environments, and in part responsible for driving poor sleep health.

Sleep quality is an important contributor to health disparities and affects the physiological function of the immune and endocrine systems, shaping how resources are allocated to life history demands. Past work in industrial and post-industrial societies has shown that lower total sleep time (TST) or more disrupted nighttime sleep are linked to flatter diurnal slopes for cortisol and lower testosterone production. There has been little focus on these physiological links in other socio-ecological settings where routine sleep conditions and nighttime activity demands differ. We collected salivary hormone (testosterone, cortisol) and actigraphy-based sleep data from Congolese BaYaka foragers (N = 39), who have relatively short and fragmented nighttime sleep, on average, in part due to their typical social sleep conditions and nighttime activity. The hormone and sleep data collections were separated by an average of 11.23 days (testosterone) and 2.84 days (cortisol). We found gendered links between nighttime activity and adults' hormone profiles. Contrary to past findings in EuroAmerican contexts, BaYaka men who were more active at night, on average, had higher evening testosterone than those with lower nighttime activity, with a relatively flat slope relating nighttime activity and evening testosterone in women. Women had steeper diurnal cortisol curves with less disrupted sleep. Men had steeper cortisol diurnal curves if they were more active at night. BaYaka men often hunt and socialize when active at night, which may help explain these patterns. Overall, our findings indicate that the nature of nighttime activities, including their possible social and subsistence contexts, are potentially important modifiers of sleep quality-physiology links, meriting further research across contexts.