Functional Disability and Social Conflict Increase Risk of Depression in Older Adulthood Among Bolivian Forager-Farmers

Post-stress Social Interaction and 3-Cyano-N-(1,3-Diphenyl-1H-Pyrazol-5-yl) Benzamide Treatment Attenuate Depressive-like Behavior Induced by Repeated Social Defeat Stress

Persistent stress increases the probability for developing depression significantly thereafter. Repeated social defeat stress is a widely used model to investigate depressive-like behavior in preclinical models. Hence, the repeated social defeat stress model provided an ideal animal model, through which the hypotheses of prevention and treatment can be investigated. We have successfully induced depressive-like behavior for male C57BL/6J mice with this model. Here, we reported that certain level of during-stress social interactions with single female or multiple male peer(s) exerted a positive role in preventing the development of depressive-like behavior induced by repeated social defeat stress. Our data suggested that the stress-susceptible mice may benefit from positive social interaction, which reduces the chance for depressive-like behavior development. Since numerous studies indicate that the metabotropic glutamate receptor 5 (mGluR5) plays an important role in various cognitive functions, we further investigate the treatment effect of 3-cyano-N-(1,3-diphenyl-1H-pyrazol-5-yl) benzamide (CDPPB) on the depressive-like behavior induced by repeated social defeat stress. Most importantly, robust anti-depressant effects have been achieved through modulating the mGluR5 function. We found that single oral dose administration of CDPPB (20 mg/kg), to some extent, alleviated the social avoidance behaviors for the stress-susceptible mice. Our data implies that the CDPPB, a positive allosteric modulator of mGluR5, is a promising anti-depressant candidate with limited side effect.

Resilience, Accelerated Aging and Persistently Poor Health: Diverse Trajectories of Health in Malawi

Individuals age at vastly different rates resulting in significant within-population heterogeneity in health and aging outcomes. This diversity in health and aging trajectories has rarely been investigated among low-income aging populations that have experienced substantial hardships throughout their lifecourses. Utilizing 2006-2018 data from the Malawi Longitudinal Study of Families and Health (MLSFH) and estimating group-based trajectory models (GBTM), our analyses identified three distinct lifecourse health trajectories: (1) comparatively good initial mental and physical health that persisted throughout the lifecourse ("resilient aging"); (2) relatively good initial mental and physical health that started to deteriorate during mid-adulthood ("accelerated aging"); and (3) poor initial mental and physical health that further declined over the lifecourse ("aging with persistently poor health"). For both physical and mental health, men were more likely to enjoy resilient aging than women. Predictors other than gender of trajectory membership sometimes confirmed, and sometimes contradicted, hypotheses derived from high-income country studies. Our analyses highlight the long arm of early life conditions and gender in determining aging trajectories and show that a non-trivial sub-population is characterized by aging with persistently poor health. The study uncovers widening gaps in health outcomes between those who age with resilience and those who experience accelerated aging.

Labour's pain: strenuous subsistence work, mechanical wear-and-tear and musculoskeletal pain in a non-industrialized population

Musculoskeletal pain is the most debilitating human health condition. Neurophysiological pain mechanisms are highly conserved and promote somatic maintenance and learning to avoid future harm. However, some chronic pain might be more common owing to mismatches between modern lifestyles and traits that originally evolved under distinct premodern conditions. To inform assumptions about factors affecting chronic pain vulnerability prior to industrialization, we assess pain prevalence, perceived causes, and predictors among Tsimane forager-horticulturalists. Habitual subsistence work is the primary reported cause of pain throughout life for both sexes, and pain is more common with age, especially in the back, and for those with more musculoskeletal problems. Sex differences in pain are relatively weak, and we find no association between women's reproductive history and pain, contrary to the hypothesis that reproduction causes women's greater pain susceptibility. Age-standardized current pain prevalence is 1.7-8.2 times higher for Tsimane than other select populations, and Tsimane chronic pain prevalence is within the range of variation observed elsewhere. Chronic low back pain is not a 'mismatch disease' limited to post-industrialized populations. Hominin musculoskeletal changes supporting bipedalism probably imposed health costs, which, after millions of years of evolution, remain an epidemiological burden that may be exacerbated by modern conditions.

Leveraging network analysis to determine sex differences in factors associated with frailty among older adults living alone

BACKGROUND

Frailty is a complex geriatric syndrome typically characterized by multiple underlying etiological factors. We determined the contributing factors, by sex, using a network analysis.

METHODS

The study sample consisted of a cross-sectional cohort of community-dwelling older adults aged ≥ 65 years living alone in a Korean city (N = 1,037). Frailty was assessed via the Korean Frailty Index. Participants were assessed for sociodemographic, health-related, mental and cognitive, and social characteristics. Mixed graphical models including all variables were estimated using the R-package mgm discretely by sex. We also used the Walktrap cluster algorithm to identify differences in the network structure in terms of connectivity around frailty between the sex groups for further insights.

RESULTS

In both the networks for males and females, frailty correlated most strongly with nutritional status, presence of complex chronic disease, and self-efficacy, and exhibited proximity to decreased sleep quality and loneliness. However, frailty showed an association with suicidal ideation and the number of falls per year only in males, whereas it showed an association with functional disabilities only in females. The overall network connectivity around frailty was stronger with dense interactions (more edges) in the network for females than for males.

CONCLUSIONS

The results signify the need for sex-group customized multi-domain assessments and interventions for the prevention and improvement of frailty among community-dwelling older adults.

Cognition and Cognitive Changes in a Low-Income Sub-Saharan African Aging Population

BACKGROUND

Cognition and its age-related changes remain vastly understudied in low-income countries (LICs), despite evidence suggesting that cognitive decline among aging low-income populations is a rapidly increasing disease burden often occurring at younger ages as compared to high-income countries (HICs).

OBJECTIVE

We examine patterns of cognition among men and women, 45 + years old, living in rural Malawi. We analyze how key socioeconomic characteristics predict levels of cognition and its changes as individuals get older.

METHODS

Utilizing the Mature Adults Cohort of the Malawi Longitudinal Study of Families and Health (MLSFH-MAC) collected during 2012-2017, we estimate standard regression models to analyze predictors of the age- and sex-specific levels and longitudinal changes in cognition. Cognition is assessed with a screening instrument that is adapted to this low-literacy context and measures different domains such as language, attention, or executive functioning.

RESULTS

Women have lower levels of cognition than men, a pattern in stark contrast to findings in HICs. Schooling and socioeconomic status increase the probability of having consistently high performance during the cognitive assessment. Cognitive decline accelerates with age and is detectable already at mid-adult ages (45-55 years). Despite lower levels of cognitive function observed among women, the pace of decline with age is similar for both genders.

CONCLUSION

Women are particularly affected by poor cognition in this context. The study emphasizes the importance of prioritizing cognitive health and research on cognition among older individuals in sub-Saharan Africa LICs, to which relatively little health care resources continue to be allocated.

How do the factors associated with frailty change with sex? An exploratory network analysis

BACKGROUND

It is important to study multiple social, physical and psychosocial factors associated with frailty in populations characterized by social and health disparities, such as men and women.

METHODS

This was a cross-sectional population-based study with older adults ≥65 years from the FIBRA (Frailty in Brazilian Older Adults) 2008-2009 study. We carried out a comparative analysis of the factors associated with the frailty phenotype in older men (N=706) and women (N=1.251) using networks based on mixed graphical models (MGM) according to sex.

RESULTS

In the male network, frailty was most strongly associated with years of schooling, overall satisfaction with life and falls; in the female network, the syndrome was associated with satisfaction with problem solving, depression and diabetes in addition to years of schooling. Furthermore, permutation tests showed that the networks for males and females were statistically different in terms of their structure, the global strength of the relationships and the strength of the relationships between frailty and diabetes; frailty and falls; frailty and depression; frailty and overall satisfaction with life; and frailty and satisfaction with problem solving (p<0.05). The walktrap network cluster detection algorithm revealed that in men, frailty was in a physical and social dimension while in women the syndrome was in a cardiometabolic and psychosocial dimension.

CONCLUSIONS

Network analysis showed that different factors are associated with frailty for each sex. The findings suggest that different strategies for dealing with frailty should be adopted for men and women so that care and prevention efforts can be directed appropriately.

The relationship of frailty and disability with suicidal ideation in late life depression

OBJECTIVES

Frailty and disability are commonly found in Late Life Depression (LLD) and have been associated with increased depression severity, health comorbidities and mortality. Additionally, physical frailty has been associated with suicide in later life, independent of presence of a mood disorder. The objective of our study was to assess the associations of physical frailty and functional disability with suicidal ideation, controlling for depression severity and demographic factors, in an older depressed sample.

METHODS

This study used data from community-dwelling older adults with major depression. Eligible participants were ≥ 65 years old, completed measures of depression symptom severity (Hamilton Depression Rating Scale-24 item; HDRS-24), current suicidal ideation (Geriatric Suicide Ideation Scale; GSIS), and physical frailty/functional capacity measures.

RESULTS

Participants were 88 older adults with a mean age of 71.5 (SD = 6.0) and 66% of the sample was female. Poorer performance on frailty measures of gait speed (B = .239, p = .003) and muscle weakness (B = -.218, p = .01) were significantly associated with higher levels of suicidal ideation, independent of depression severity and demographic factors. Functional disability was also significantly related to suicide ideation, specifically impairment in financial capacity (B = -.290, p = .008), social interaction (B = .408, p < .001), and communication skills (B = .373, p = .001).

CONCLUSION

Our findings show that, in LLD, frailty and functional disability are significantly associated with higher levels of suicide ideation, independent of depression symptom severity.

Collapsin response mediator protein 5 (CRMP5) modulates susceptibility to chronic social defeat stress in mice

Collapsin response mediator protein 5 (CRMP5), a member of the CRMP family, is expressed in the brain, particularly in the hippocampus, an area of the brain that can modulate stress responses. Social stress has a well-known detrimental effect on health and can lead to depression, but not all individuals are equally sensitive to stress. To date, researchers have not conclusively determined how social stress increases the susceptibility of the brain to depression. Here, we used the chronic social defeat stress (CSDS) model and observed higher hippocampal CRMP5 expression in stress-susceptible (SS) mice than in control and stress-resilient (RES) mice. A negative correlation was observed between the expression levels of CRMP5 and the social interaction (SI) ratio. Reduced hippocampal CRMP5 expression increased the SI ratio in SS mice, whereas CRMP5 overexpression was sufficient to induce social avoidance behaviors in control mice following exposure to subthreshold social stress induced by lentivirus-based overexpression and inducible tetracycline-on strategies to upregulate CRMP5. Interestingly, increased CRMP5 expression in SS and lenti-CRMP5-treated mice also caused serum corticosterone concentrations to increase. These findings improve our understanding of the potential mechanism by which CRMP5 triggers susceptibility to social stress, and they support the further development of therapeutic agents for the treatment of stress disorders in humans.

Evaluating social contract theory in the light of evolutionary social science

Political philosophers have long drawn explicitly or implicitly on claims about the ways in which human behaviour is shaped by interactions within society. These claims have usually been based on introspection, anecdotes or casual empiricism, but recent empirical research has informed a number of early views about human nature. We focus here on five components of such views: (1) what motivates human beings; (2) what constraints our natural and social environments impose upon us; (3) what kind of society emerges as a result; (4) what constitutes a fulfilling life; and (5) what collective solutions can improve the outcome. We examine social contract theory as developed by some early influential political philosophers (Hobbes, Locke and Rousseau), who viewed the social contract as a device to compare the 'natural' state of humans with their behaviour in society. We examine their views in the light of recent cross-cultural empirical research in the evolutionary social sciences. We conclude that social contract theorists severely underestimated human behavioural complexity in societies lacking formal institutions. Had these theorists been more informed about the structure and function of social arrangements in small-scale societies, they might have significantly altered their views about the design and enforcement of social contracts.

Productivity loss associated with functional disability in a contemporary small-scale subsistence population

In comparative cross-species perspective, humans experience unique physical impairments with potentially large consequences. Quantifying the burden of impairment in subsistence populations is critical for understanding selection pressures underlying strategies that minimize risk of production deficits. We examine among forager-horticulturalists whether compromised bone strength (indicated by fracture and lower bone mineral density, BMD) is associated with subsistence task cessation. We also estimate the magnitude of productivity losses associated with compromised bone strength. Fracture is associated with cessation of hunting, tree chopping, and walking long distances, but not tool manufacture. Age-specific productivity losses from hunting cessation associated with fracture and lower BMD are substantial: ~397 lost kcals/day, with expected future losses of up to 1.9 million kcals (22% of expected production). Productivity loss is thus substantial for high strength and endurance tasks. Determining the extent to which impairment obstructs productivity in contemporary subsistence populations improves our ability to infer past consequences of impairment.

Key Risk Factors Affecting Farmers' Mental Health: A Systematic Review

Recently, concern has increased globally over farmers' mental health issues. We present a systematic review of the outcomes, locations, study designs, and methods of current studies on farmers' mental health. In particular, this review aims to fill an important gap in understanding of the potential key risk factors affecting farmers' mental health around the world. 167 articles on farmer mental health were included in a final systematic review using a standardized electronic literature search strategy and PRISMA guidelines. The four most-cited influences on farmers' mental health in the reviewed literature respectively were pesticide exposure, financial difficulties, climate variabilities/drought, and poor physical health/past injuries. The majority of studies were from developed countries, most specifically from the United States, Australia, and the United Kingdom. Comparative studies on the mental health of farmers and other occupational workers showed mixed results, with a larger portion identifying that psychological health disturbances were more common in farmers and farm-workers. Knowledge of farmer psychological disorder risk factors and its impacts are essential for reducing the burden of mental illness. Further research will be required on climate change impacts, developing country farmers' mental health, and information on how to reduce help-seeking barriers amongst farmers.

Mental health is biological health: Why tackling "diseases of the mind" is an imperative for biological anthropology in the 21st century

The germ theory of disease and the attendant public health initiatives, including sanitation, vaccination, and antibiotic treatment, led to dramatic increases in global life expectancy. As the prevalence of infectious disease declines, mental disorders are emerging as major contributors to the global burden of disease. Scientists understand little about the etiology of mental disorders, however, and many of the most popular psychopharmacological treatments, such as antidepressants and antipsychotics, have only moderate-to-weak efficacy in treating symptoms and fail to target biological systems that correspond to discrete psychiatric syndromes. Consequently, despite dramatic increases in the treatment of some mental disorders, there has been no decrease in the prevalence of most mental disorders since accurate record keeping began. Many researchers and theorists are therefore endeavoring to rethink psychiatry from the ground-up. Anthropology, especially biological anthropology, can offer critical theoretical and empirical insights to combat mental illness globally. Biological anthropologists are unique in that we take a panhuman approach to human health and behavior and are trained to address each of Tinbergen's four levels of analysis as well as culture. The field is thus exceptionally well-situated to help resolve the mysteries of mental illness by integrating biological, evolutionary, and sociocultural perspectives.

A biocultural approach to psychiatric illnesses

RATIONALE

As a species, humans are vulnerable to numerous mental disorders, including depression and schizophrenia. This susceptibility may be due to the evolution of our large, complex brains, or perhaps because these illnesses counterintuitively confer some adaptive advantage. Additionally, cultural and biological factors may contribute to susceptibility and variation in mental illness experience and expression. Taking a holistic perspective could strengthen our understanding of these illnesses in diverse cultural contexts.

OBJECTIVES

This paper reviews some of these potential factors and contextualizes mental disorders within a biocultural framework.

RESULTS

There is growing evidence that suggests cultural norms may influence inflammation, neurotransmitters, and neurobiology, as well as the illness experience. Specific examples include variation in schizophrenia delusions between countries, differences in links between inflammation and emotion between the United States and Japan, and differences in brain activity between Caucasian and Asian participants indicating that cultural values may moderate cognitive processes related to social cognition and interoception.

CONCLUSIONS

Research agendas that are grounded in an appreciation of biocultural diversity as it relates to psychiatric illness represent key areas for truly interdisciplinary research that can result in culturally sensitive treatments and highlight possible biological variation affecting medical treatment.

Broadening horizons: Sample diversity and socioecological theory are essential to the future of psychological science

The present lack of sample diversity and ecological theory in psychological science fundamentally limits generalizability and obstructs scientific progress. A focus on the role of socioecology in shaping the evolution of morphology, physiology, and behavior has not yet been widely applied toward psychology. To date, evolutionary approaches to psychology have focused more on finding universals than explaining variability. However, contrasts between small-scale, kin-based rural subsistence societies and large-scale urban, market-based populations, have not been well appreciated. Nor has the variability within high-income countries, or the socioeconomic and cultural transformations affecting even the most remote tribal populations today. Elucidating the causes and effects of such broad changes on psychology and behavior is a fundamental concern of the social sciences; expanding study participants beyond students and other convenience samples is necessary to improve understanding of flexible psychological reaction norms among and within populations. Here I highlight two examples demonstrating how socioecological variability can help explain psychological trait expression: (i) the role of environmental harshness and unpredictability on shaping time preference and related traits, such as impulsivity, vigilance, and self-efficacy; and (ii) the effects of industrialization, market integration, and niche complexity on personality structure. These cases illustrate how appropriate theory can be a powerful tool to help determine choices of diverse study populations and improve the social sciences.

Exploring chronic disease in Bolivia: A cross-sectional study in La Paz

Purpose

This study seeks to develop an understanding that can guide development of programs to improve health and care for individuals with Non-Communicable Diseases (NCDs) in La Paz, Bolivia, where NCDs are prevalent and primary care systems are weak. This exploratory investigation examines the characteristics of chronic disease patients in the region, key health related behaviors, and their perceptions of the care that they receive. The longer-term goal is to lay groundwork for interventional studies based on the principles of the Chronic Care Model (CCM).

Subjects and methods

The study is based on two surveys of adults (> 18 years old) administered in 2014 in La Paz, Bolivia. A total of 1165 adult patients participated in the first screening survey. A post-screening second survey, administered only on those who qualified based on Survey 1, collected more detailed information about the subjects’ general health and health related personal circumstances, several health behaviors, health literacy, and their perceptions of care received. A final data set of 651 merged records were used for analysis.

Results

Characteristic of a low-income country, the majority of participants had low levels of education, income, health literacy and high rates of under/unemployment. Nearly 50% of participants reported 2 or more NCDs. Seventy-four percent (74%) of respondents reported low levels of medication adherence and 26% of the population was found to have an undiagnosed depressive disorder. Overall, the perception of care quality was low (60%), particularly in those under the age of 45. Significant relationships emerged between several sociodemographic characteristics, health behaviors, and perceptions that have major implications for improving NCD care in this population.

Conclusions

These findings illustrate some of the challenges facing low-income countries where reversing the tide of NCDs is of great importance. The prevalence of NCDs coupled with challenging social determinants of health, poor medication adherence, low health literacy, and perceptions of low quality of healthcare highlight several areas of opportunity for intervention.

The Demography of Mental Health Among Mature Adults in a Low-Income, High-HIV-Prevalence Context

Very few studies have investigated mental health in sub-Saharan Africa (SSA). Using data from Malawi, this article provides a first picture of the demography of depression and anxiety (DA) among mature adults (aged 45 or older) in a low-income country with high HIV prevalence. DA are more frequent among women than men, and individuals affected by one are often affected by the other. DA are associated with adverse outcomes, such as poorer nutrition intake and reduced work efforts. DA also increase substantially with age, and mature adults can expect to spend a substantial fraction of their remaining lifetime-for instance, 52 % for a 55-year-old woman-affected by DA. The positive age gradients of DA are not due to cohort effects, and they are in sharp contrast to the age pattern of mental health that has been shown in high-income contexts, where older individuals often experience lower levels of DA. Although socioeconomic and risk- or uncertainty-related stressors are strongly associated with DA, they do not explain the positive age gradients and gender gap in DA. Stressors related to physical health, however, do. Hence, our analyses suggest that the general decline of physical health with age is the key driver of the rise of DA with age in this low-income SSA context.

The association of Social Anxiety Disorder, Alcohol Use Disorder and reproduction: Results from four nationally representative samples of adults in the USA

Social Anxiety Disorder (SAD) and Alcohol Use Disorder (AUD) are highly prevalent and frequently co-occur. The results of population studies suggest that SAD tends to precede AUD, and the results of laboratory studies suggest that alcohol use facilitates social behaviors in socially anxious individuals. Therefore, we posited that, in a modern context, a tendency to consume alcohol may be positively selected for among socially anxious individuals by its effect on the likelihood of finding a partner and reproducing. We tested the hypothesis that a higher proportion of individuals with a lifetime diagnosis of SAD and AUD reproduce (i.e., have at least one child) relative to individuals with SAD absent AUD in an individual participant meta-analysis based on over 65,000 adults derived from four nationally representative cross-sectional samples. We then cross-validated these findings against the results of a 10-year follow up of one of these surveys. Lifetime history of SAD was not associated with reproduction whereas lifetime history of AUD was positively associated with reproduction. There was no statistically detectable difference in the proportion of individuals with a lifetime history of SAD with or without AUD who reproduced. There was considerable heterogeneity in all of the analyses involving SAD, suggesting that there are likely to be other pertinent variables relating to SAD and reproduction that should be delineated.

Aging Perceptions in Tsimane' Amazonian Forager-Farmers Compared With Two Industrialized Societies

Objectives

Cross-cultural studies suggest that aging attitudes show some variation across societies, but this evidence is mostly drawn from industrialized settings. The limited research record on pre-industrial societies is largely qualitative in nature. The present study targeted this gap by adapting an existing multidimensional measure of aging attitudes for use in traditional populations and administering it to samples from one traditional society and two industrialized societies.

Method

We administered the adapted multidimensional measure of aging attitudes to samples from one traditional society (Tsimane' Amazonian forager-farmers in Bolivia, n = 90) and two industrialized societies (the United States, n = 91, and Poland, n = 100).

Results

Across societies, aging perceptions were more favorable for respect and wisdom than for other domains of functioning, and women were perceived to be aging less favorably. Further, the Tsimane' reported more positive aging perceptions than the U.S. and Polish samples, especially with regard to memory functioning. Within the Tsimane' sample, there was no evidence of an influence of acculturation on aging perceptions.

Discussion

The present study contributed to our understanding of cross-cultural differences in aging attitudes. Theoretical implications and directions for future research are discussed.

The Tsimane Health and Life History Project: Integrating anthropology and biomedicine

The Tsimane Health and Life History Project, an integrated bio-behavioral study of the human life course, is designed to test competing hypotheses of human life-history evolution. One aim is to understand the bidirectional connections between life history and social behavior in a high-fertility, kin-based context lacking amenities of modern urban life (e.g. sanitation, banks, electricity). Another aim is to understand how a high pathogen burden influences health and well-being during development and adulthood. A third aim addresses how modernization shapes human life histories and sociality. Here we outline the project's goals, history, and main findings since its inception in 2002. We reflect on the implications of current findings and highlight the need for more coordinated ethnographic and biomedical study of contemporary nonindustrial populations to address broad questions that can situate evolutionary anthropology in a key position within the social and life sciences.

Pathogen-Host Defense in the Evolution of Depression: Insights into Epidemiology, Genetics, Bioregional Differences and Female Preponderance

Significant attention has been paid to the potential adaptive value of depression as it relates to interactions with people in the social world. However, in this review, we outline the rationale of why certain features of depression including its environmental and genetic risk factors, its association with the acute phase response and its age of onset and female preponderance appear to have evolved from human interactions with pathogens in the microbial world. Approaching the relationship between inflammation and depression from this evolutionary perspective yields a number of insights that may reveal important clues regarding the origin and epidemiology of the disorder as well as the persistence of its risk alleles in the modern human genome.

Cognitive performance across the life course of Bolivian forager-farmers with limited schooling

Cognitive performance is characterized by at least two distinct life course trajectories. Many cognitive abilities (e.g., "effortful processing" abilities, including fluid reasoning and processing speed) improve throughout early adolescence and start declining in early adulthood, whereas other abilities (e.g., "crystallized" abilities like vocabulary breadth) improve throughout adult life, remaining robust even at late ages. Although schooling may impact performance and cognitive "reserve," it has been argued that these age patterns of cognitive performance are human universals. Here we examine age patterns of cognitive performance among Tsimane forager-horticulturalists of Bolivia and test whether schooling is related to differences in cognitive performance over the life course to assess models of active versus passive cognitive reserve. We used a battery of eight tasks to assess a range of latent cognitive traits reflecting attention, processing speed, verbal declarative memory, and semantic fluency (n = 919 individuals, 49.9% female). Tsimane cognitive abilities show similar age-related differences as observed in industrialized populations: higher throughout adolescence and only slightly lower in later adulthood for semantic fluency but substantially lower performance beginning in early adulthood for all other abilities. Schooling is associated with greater cognitive abilities at all ages controlling for sex but has no attenuating effect on cognitive performance in late adulthood, consistent with models of passive cognitive reserve. We interpret the minimal attenuation of semantic fluency late in life in light of evolutionary theories of postreproductive life span, which emphasize indirect fitness contributions of older adults through the transfer of information, labor, and food to descendant kin. (PsycINFO Database Record

Explaining the sex difference in depression with a unified bargaining model of anger and depression

BACKGROUND

Women are twice as likely as men to be depressed, a bias that is poorly understood. One evolutionary model proposes that depression is a bargaining strategy to compel reluctant social partners to provide more help in the wake of adversity. An evolutionary model of anger proposes that high upper body strength predisposes individuals to angrily threaten social partners who offer too few benefits or impose too many costs. Here, we propose that when social partners provide too few benefits or impose too many costs, the physically strong become overtly angry and the physically weak become depressed. The sexual dimorphism in upper body strength means that men will be more likely to bargain with anger and physical threats and women with depression.

METHODOLOGY

We tested this idea using the 2011-12 National Health and Nutrition Examination Survey (NHANES), a large nationally representative sample of US households that included measures of depression and upper body strength.

RESULTS

A 2 SD increase in grip strength decreased the odds of depression by more than half ([Formula: see text],[Formula: see text]), which did not appear to be a consequence of confounds with anthropometric, hormonal or socioeconomic variables, but was partially explained by a confound with physical disability. Nevertheless, upper body strength mediated 63% of the effect of sex on depression, but the mediation effect was unexpectedly moderated by age.

CONCLUSIONS

Low upper body strength is a risk factor for depression, especially in older adults, and the sex difference in body strength appears to explain much of the perplexing sex difference in depression.

Depression as sickness behavior? A test of the host defense hypothesis in a high pathogen population

Sadness is an emotion universally recognized across cultures, suggesting it plays an important functional role in regulating human behavior. Numerous adaptive explanations of persistent sadness interfering with daily functioning (hereafter "depression") have been proposed, but most do not explain frequent bidirectional associations between depression and greater immune activation. Here we test several predictions of the host defense hypothesis, which posits that depression is part of a broader coordinated evolved response to infection or tissue injury (i.e. "sickness behavior") that promotes energy conservation and reallocation to facilitate immune activation. In a high pathogen population of lean and relatively egalitarian Bolivian forager-horticulturalists, we test whether depression and its symptoms are associated with greater baseline concentration of immune biomarkers reliably associated with depression in Western populations (i.e. tumor necrosis factor alpha [TNF-α], interleukin-1 beta [IL-1β], interleukin-6 [IL-6], and C-reactive protein [CRP]). We also test whether greater pro-inflammatory cytokine responses to ex vivo antigen stimulation are associated with depression and its symptoms, which is expected if depression facilitates immune activation. These predictions are largely supported in a sample of older adult Tsimane (mean±SD age=53.2±11.0, range=34-85, n=649) after adjusting for potential confounders. Emotional, cognitive and somatic symptoms of depression are each associated with greater immune activation, both at baseline and in response to ex vivo stimulation. The association between depression and greater immune activation is therefore not unique to Western populations. While our findings are not predicted by other adaptive hypotheses of depression, they are not incompatible with those hypotheses and future research is necessary to isolate and test competing predictions.

Low mineral density of a weight-bearing bone among adult women in a high fertility population

Evolutionary theories of aging posit that greater reproductive effort causes somatic decline given a fundamental trade-off between investing energy in reproduction and repair. Few studies in high fertility human populations support this hypothesis, and problems of phenotypic correlation can obscure the expected trade-off between reproduction and somatic condition. This cross-sectional study investigates whether greater reproductive effort is associated with reduced calcaneal bone mineral density (BMD) among female Tsimane forager-farmers of lowland Bolivia. We also investigate whether female Tsimane BMD values are lower than sex- and age-matched US reference values, despite the fact that Tsimane engage in higher physical activity levels that can increase mechanical loading. To measure calcaneal BMD, quantitative ultrasonography was performed on 130 women (mean ± SD age = 36.6 ± 15.7, range = 15-75) that were recruited regardless of past or current reproductive status. Anthropometric and demographic data were collected during routine medical exams. As predicted, higher parity, short inter-birth interval, and earlier age at first birth are associated with reduced BMD among Tsimane women after adjusting for potential confounders. Population-level differences are apparent prior to the onset of reproduction, and age-related decline in BMD is greater among Tsimane compared with American women. Greater cumulative reproductive burden may lower calcaneal BMD individually and jointly with other lifestyle and heritable factors. Fitness impacts of kin transfers in adulthood may determine the value of investments in bone remodeling, and thus affect selection on age-profiles of bone mineral loss.

Depression and Frailty in Late Life: Evidence for a Common Vulnerability

OBJECTIVES

The study purpose is to estimate the correlation between depression and competing models of frailty, and to determine to what degree the comorbidity of these syndromes is determined by shared symptomology.

METHODS

Data come from the 2010 Health and Retirement Study. Analysis was limited to community-dwelling participants 65 and older (N = 3,453). Depressive symptoms were indexed by the 8-item Centers for Epidemiologic Studies Depression (CESD) scale. Frailty was indexed by 3 alternative conceptual models: (a) biological syndrome, (b) frailty index, and (c) functional domains. Confirmatory factor analysis (CFA) was used to estimate the correlation between depression and each model of frailty.

RESULTS

Each of the 3 frailty latent factors was significantly correlated with depression: biological syndrome (ρ = .68, p < .01), functional domains (ρ = .70, p < .01), and frailty index (ρ = .61, p < .01). Substantial correlation remained when accounting for shared symptoms between depression and the biological syndrome (ρ = .45) and frailty index (ρ = .56) models.

DISCUSSION

Results indicate that the correlation of frailty and depression in late life is substantial. The association between the two constructs cannot be fully explained by symptom overlap, suggesting that psychological vulnerability may be an important component of frailty.

Darwinian depression

BACKGROUND

The standard evolutionary explanation for depression is that being in an emotionally depressed state is adaptive.

METHOD

The article first undertakes a critical review of the extant literature. It then provides an alternative evolutionary explanation for event-based depression and elation. It argues that being in a depressed state is not adaptive (indeed, quite the opposite), but that the threat of depression for bad outcomes and the promise of pleasure for good outcomes are adaptive because they motivate the individual toward undertaking effort that increases fitness. The article then explains reasons for failure in the motivation system and the mood disorders that arise as a consequence.

RESULTS

The article explains why motivation depends on both elation and depression and why individual happiness is not permanently improved by winning the lottery (or permanently reduced by becoming wheelchair bound). It explains the comorbidity of bipolar disorder and panic disorder, why mood stabilizers tend to reduce motivation, and when anti-depressants are unlikely to cure "laziness."

LIMITATIONS

The evolutionary explanation for depression does not directly provide clinical criteria for determining when major depressive disorder is present nor has it yet provided new treatment strategies for mood disorders.

CONCLUSIONS

The theory presented here provides a coherent explanation for depression and elation and leads research in a different direction from previous evolutionary explanations.