Samuel S. Urlacher

• PhD
• Professor (Assistant) at Baylor University

Autoimmune diseases and allergic reactions occur when the immune system becomes dysregulated and mistakenly targets self-produced or harmless antigens 1. These conditions can contribute to pregnancy complications, including miscarriage and recurrent pregnancy loss 2. We hypothesize that diagnosed immunological disorders and elevated levels of innat...

Objectives Reproductive effort incurs the cost of biological aging and morbidity by compromising somatic maintenance when key resources are limited. Oxidative stress is positively correlated with reproductive effort in adult human females and non‐human male animal models, but human males are understudied. We hypothesized that due to its anabolic an...

Objective Extreme climatic events, like droughts, are increasing in frequency and severity. Droughts disrupt community livelihoods and resources with serious implications for human biology. This study investigated how chronic stress, measured by fingernail cortisol concentration (FCC), and water insecurity status were predictive of C‐reactive prote...

Oxidative stress (OS) is a key biological challenge and selective pressure for organisms with aerobic metabolism. The result of the imbalance between reactive oxygen species production and antioxidant defense, OS can damage proteins, lipids, and nucleic acids and plays an important role in driving variation in biological aging and health. Among hum...

Nutritional epidemiology aims to link dietary exposures to chronic disease, but the instruments for evaluating dietary intake are inaccurate. One way to identify unreliable data and the sources of errors is to compare estimated intakes with the total energy expenditure (TEE). In this study, we used the International Atomic Energy Agency Doubly Labe...

Background Rising global obesity rates are linked with inflammation and associated morbidities. These negative outcomes are generally more common in low-resource communities within high-income countries; however, it is unclear how frequent infectious disease exposures in these settings may influence the relationship between adiposity and inflammati...

Objectives The hypothalamic–pituitary–adrenal (HPA) axis and its primary end product, the glucocorticoid cortisol, are major components of the evolved human stress response. However, most studies have examined these systems among populations in high‐income settings, which differ from the high pathogen and limited resource contexts in which the HPA...

Objectives Chronic immune activation and severe inflammatory states are positively associated with resting metabolic rate (RMR; kcal/day), but the impacts of mild immune stimuli on metabolism are poorly understood. This study investigates the within-individual association between the inflammatory response to influenza vaccination and RMR in young a...

Noncommunicable diseases (NCDs) are on the rise worldwide. Obesity, cardiovascular disease, and type 2 diabetes are among a long list of “lifestyle” diseases that were rare throughout human history but are now common. The evolutionary mismatch hypothesis posits that humans evolved in environments that radically differ from those we currently experi...

To address claims of human exceptionalism, we determine where humans fit within the greater mammalian distribution of reproductive inequality. We show that humans exhibit lower reproductive skew (i.e., inequality in the number of surviving offspring) among males and smaller sex differences in reproductive skew than most other mammals, while neverth...

Obesity is caused by a prolonged positive energy balance1,2. Whether reduced energy expenditure stemming from reduced activity levels contributes is debated3,4. Here we show that in both sexes, total energy expenditure (TEE) adjusted for body composition and age declined since the late 1980s, while adjusted activity energy expenditure increased ove...

Globally, we are witnessing the rise of complex, non-communicable diseases (NCDs) related to changes in our daily environments. Obesity, asthma, cardiovascular disease, and type 2 diabetes are part of a long list of "lifestyle" diseases that were rare throughout human history but are now common. A key idea from anthropology and evolutionary biology...

Globally, we are witnessing the rise of complex, non-communicable diseases (NCDs) related to changes in our daily environments. Obesity, asthma, cardiovascular disease, and type 2 diabetes are part of a long list of "lifestyle" diseases that were rare throughout human history but are now common. A key idea from anthropology and evolutionary biology...

Abstract: Helicobacter pylori infections disproportionately affect certain populations more than others, especially those residing in resource-poor areas. Sex-specific factors may also impact the virulence and pathogenicity of H. pylori. Estradiol, the primary female sex hormone, may contribute to H. pylori by increasing absorption. However, estrad...

Water is essential for survival, but one in three individuals worldwide (2.2 billion people) lacks access to safe drinking water. Water intake requirements largely reflect water turnover (WT), the water used by the body each day. We investigated the determinants of human WT in 5604 people from the ages of 8 days to 96 years from 23 countries using...

Background: The use of minimally invasive biomarkers (MIBs – physiological biomarkers obtained from minimally invasive sample types) has expanded rapidly in science and medicine over the past several decades. The MIB approach is a methodological strength in the field of human and non-human primate evolutionary biology (HEB). Among humans and our cl...

In mammals, trait variation is often reported to be greater among males than females. However, to date, mainly only morphological traits have been studied. Energy expenditure represents the metabolic costs of multiple physical, physiological, and behavioral traits. Energy expenditure could exhibit particularly high greater male variation through a...

Lower ambient temperature (Ta) requires greater energy expenditure to sustain body temperature. However, effects of Ta on human energetics may be buffered by environmental modification and behavioral compensation. We used the IAEA DLW database for adults in the USA (n = 3213) to determine the effect of Ta (-10 to +30°C) on TEE, basal (BEE) and acti...

The health consequences of soil-transmitted helminth (STH) infections are often attributed to parasite-caused tissue damage and nutrient loss, combined with immune energy costs. However, this view overlooks additional pathways by which infection can alter host energetics. Here, we take a first step toward defining this suite of energetic pathways a...

Low total energy expenditure (TEE, MJ/d) has been a hypothesized risk factor for weight gain, but repeatability of TEE, a critical variable in longitudinal studies of energy balance, is understudied. We examine repeated doubly labeled water (DLW) measurements of TEE in 348 adults and 47 children from the IAEA DLW Database (mean ± SD time interval:...

Objective Cytomegalovirus (CMV) infection is associated with age-related chronic disease, and co-infection with Epstein-Barr virus (EBV) may compound disease risk. We aimed to assess the frequency of CMV infection and its relationship with age among EBV seropositive individuals in an Indigenous Amazonian population. Methods We report concentration...

Background: Physical activity may be a way to increase and maintain fat-free mass (FFM) in later life, similar to the prevention of fractures by increasing peak bone mass. Objectives: A study is presented of the association between FFM and physical activity in relation to age. Methods: In a cross-sectional study, FFM was analyzed in relation t...

A lifetime of change Measurements of total and basal energy in a large cohort of subjects at ages spanning from before birth to old age document distinct changes that occur during a human lifetime. Pontzer et al . report that energy expenditure (adjusted for weight) in neonates was like that of adults but increased substantially in the first year o...

Understanding the impacts of activity on energy balance is crucial. Increasing levels of activity may bring diminishing returns in energy expenditure because of compensatory responses in non-activity energy expenditures.1, 2, 3 This suggestion has profound implications for both the evolution of metabolism and human health. It implies that a long-te...

To sustain life, humans and other terrestrial animals must maintain a tight balance of water gain and water loss each day.1-3 However, the evolution of human water balance physiology is poorly understood due to the absence of comparative measures from other hominoids. While humans drink daily to maintain water balance, rainforest-living great apes...

Objective Anemia is an important global health challenge. We investigate anemia prevalence among Indigenous Shuar of Ecuador to expand our understanding of population‐level variation, and to test hypotheses about how anemia variation is related to age, sex, and market integration. Methods Hemoglobin levels were measured in a total sample of 1650 S...

Significance Disgust likely evolved to regulate exposure to pathogen-related stimuli and behaviors. One key prediction, that individuals with greater pathogen disgust sensitivity (PDS) will be exposed to fewer pathogens and thus suffer fewer infections, has never been tested directly. To function adaptively, PDS must respond to the local cost/benef...

The doubly labeled water (DLW) method measures total energy expenditure (TEE) in free-living subjects. Several equations are used to convert isotopic data into TEE. Using the International Atomic Energy Agency (IAEA) DLW database (5,756 measurements of adults and children), we show considerable variability is introduced by different equations. The...

Background Childhood overweight and obesity (OW/OB) is increasingly centered in low- and middle-income countries (LMICs) as rural populations experience market integration and lifeway change. Most explanatory studies have relied on imprecise estimates of children's energy expenditure, restricting understanding of the relative effects of changes in...

Background Soil-transmitted helminth (STH) infections have many negative health outcomes (e.g., diarrhea, nutritional deficiencies) that can also exacerbate poverty. These infections are generally highest among low-income populations, many of which are also undergoing market integration (MI; increased participation in a market-based economy). Yet t...

Children’s metabolic energy expenditure is central to evolutionary and epidemiological frameworks for understanding variation in human phenotype and health. Nonetheless, the impact of a physically active lifestyle and heavy burden of infectious disease on child metabolism remains unclear. Using energetic, activity, and biomarker measures, we show t...

Objectives: This study investigates bone density across the life course among Bolivian Tsimane and Ecuadorian Shuar of Amazonia. Both groups are rural, high-fertility forager-horticulturalists, with high lifetime physical activity levels. We test whether Tsimane and Shuar bone density patterns are different from each other, and if both groups are...

Objectives: Little research exists documenting levels of intestinal inflammation among indigenous populations where exposure to macroparasites, like soil-transmitted helminths (STHs), is common. Reduced STH exposure is hypothesized to contribute to increased prevalence of elevated intestinal inflammation in wealthy nations, likely due to coevoluti...

Objectives We measured total energy expenditure (TEE; kcal/d) and water throughput (L/d) among Shuar forager‐horticulturalists from Amazonian Ecuador to compare their daily energy and water demands to adults in other small‐scale and industrialized populations. Methods TEE and water throughput were measured using the doubly labeled water method amo...

Intimate partner violence (IPV) is a critical public health issue that impacts women and children across the globe. Prior studies have documented that maternal experiences of IPV are associated with adverse psychological and physical health outcomes in children; however, research on the underlying physiological pathways linking IPV to these conditi...

Mortality and morbidity are key factors influencing the evolution of human biology, behavior, and life history. But how have medical advancements affected human mortality in the context of the Epidemiological Transition, where falling rates of illness and death due to infectious diseases are being replaced by increasing rates of chronic illness and...

Significance The energetic impact of immune function on human growth remains unclear. Using data from Amazonian forager-horticulturalists, we show that diverse, low-level immune activity predicts reduced childhood growth over periods of competing energy use ranging from 1 wk to 20 mo. We also demonstrate that modest body fat stores (i.e., energy re...

Economic development is marked by dramatic increases in the incidence of microbiome-associated diseases, such as autoimmune diseases and metabolic syndromes, but the lifestyle changes that drive alterations in the human microbiome are not known. We measured market integration as a proxy for economically related lifestyle attributes, such as ownersh...

Despite broad implications for understanding human life history, energetics, and health, the impact of physical activity on childhood growth remains unclear. Particularly understudied is the effect of secular changes in physical activity on child development. We address these shortcomings using data spanning the transition from traditional to semi-...

The hypothalamic–pituitary–adrenal (HPA) axis represents an important and evolutionarily ancient biological pathway linking physical and psychological stressors with human health. Despite considerable research exploring the physiological stress response among developed populations, few studies have examined HPA activity in non-industrialized contex...

Social hierarchy exists in all human societies, yet the characteristics important for achieving high social status may differ cross-culturally. Studies among Western industrialized populations often use indices of socioeconomic status (SES) to determine individual social position. Conversely, studies among small-scale societies typically use locall...

Tapeworms are parasitic flatworms (class: Cestoidea). They differ from soil-transmitted helminths (STHs; class: Nematoda) in biology, physiology, and mode of transmission. Tapeworms are contracted through consumption of infected meat or fecally-contaminated foods, and can result in abdominal pain, diarrhea and nutritional deficiencies. Prior to 201...

Background Soil-transmitted helminth (STH) infection peaks during childhood and varies by sex. The impact of market integration (MI) (increasing production for and consumption from a market-based economy) on these infection patterns, however, is unclear. In this study, STH infection is examined by sex and age among indigenous Shuar inhabiting two r...

Objectives: Growth standards and references currently used to assess population and individual health are derived primarily from urban populations, including few individuals from indigenous or subsistence groups. Given environmental and genetic differences, growth may vary in these populations. Thus, there is a need to assess whether international...

Background: Market integration (MI)-increasing production for and consumption from a market-based economy-is drastically altering traditional ways of life and environmental conditions among indigenous Amazonian peoples. The effects of MI on the biology and health of Amazonian children and adolescents, however, remain unclear. Aim: This study exa...

Our objective was to validate a commercially available ELISA to measure antibody titers against Epstein-Barr virus (EBV) in dried blood spots (DBS) to replace a previously validated assay for DBS that is no longer available. We evaluated the precision, reliability, and stability of the assay for the measurement of EBV antibodies in matched plasma,...

Objectives: Knemometry, the precise measurement of lower leg (LL) length, suggests that childhood short-term (e.g., weekly) growth is a dynamic, nonlinear process. However, owing to the large size and complexity of the traditional knemometer device, previous study of short-term growth among children has been restricted predominantly to clinical se...

Information concerning physical growth among small-scale populations remains limited, yet such data are critical to local health efforts and to foster basic understandings of human life history and variation in childhood development. Using a large dataset and robust modeling methods, this study aims to describe growth from birth to adulthood among...

Objectives Cultural practices may compromise the accuracy of salivary hormone measurements and must be considered when designing human biology research protocols. This study aims to evaluate the acute effect of one common human practice—chewing betel nut—on the measurement of salivary cortisol levels under field conditions.Materials and Methods Dat...

Cassava beer, or chicha, is typically consumed daily by the indigenous Shuar people of the Ecuadorian Amazon. This traditional beverage made from cassava tuber (Manihot esculenta) is thought to improve nutritional quality and flavor while extending shelf life in a tropical climate. Bacteria responsible for chicha fermentation could be a source of m...

Abstract Soil-transmitted helminth (STH) infections can result in a variety of negative health outcomes (e.g., diarrhea, nutritional deficiencies). Market integration (MI; participation in market-based economies) has been suggested to alter levels of STH exposure due to associated changes in diet, sanitation, and behavior, but the effects are compl...

Cassava beer, or chicha , is typically consumed daily by the indigenous Shuar people of the Ecuadorian Amazon. This traditional beverage made from cassava tuber ( Manihot esculenta ) improves nutritional quality and flavor while extending shelf life in a tropical climate. Bacteria responsible for chicha fermentation could be a source of microbes be...

Cassava beer, or chicha , is typically consumed daily by the indigenous Shuar people of the Ecuadorian Amazon. This traditional beverage made from cassava tuber ( Manihot esculenta ) improves nutritional quality and flavor while extending shelf life in a tropical climate. Bacteria responsible for chicha fermentation could be a source of microbes be...

Background: James Tanner's landmark publication, Growth at Adolescence, was not only the first and most comprehensive treatise on the subject of human pubertal development of its time, its core insights have held up remarkably well over time. Review: This review connects Tanner's contributions to contemporary understanding of puberty as a proces...