Samuel S. Urlacher, Ph.D.
Associate Professor & Graduate Program Director of Anthropology Baylor University
- Waco TX
Renowned anthropologist & human evolutionary biologist specializing in global variation in child development, metabolism, and health.
Media
Biography
His collaborative research program integrates lab and field research (currently on 5 continents) and draws from many disciplines, including evolutionary biology, anthropology, immunology, nutrition science, psychology, economics, and epidemiology. He is particularly interested in how children allocate calories to competing physiological tasks (e.g., brain development, immune activity, and growth) and the impact of early adversity on lifetime metabolic disease risk (e.g., obesity and chronic inflammation). Much of his current work (funded by NIH, NSF, and others) uses stable isotope-tracking methods to investigate the changes in children’s energy expenditure that may underlie the global nutrition/epidemiologic transition. An important goal of this work is to apply research findings to improve health outcomes.
Areas of Expertise
Accomplishments
Azrieli Global Scholar
CIFAR
2020-2024
Michael A. Little Early Career Award
The Human Biology Association
2024
Education
Harvard University
Ph.D.
Human Evolutionary Biology
2016
Harvard University
M.A.
Human Evolutionary Biology
2012
Brown University
B.S.
Human Biology and Anthropology
2009
Affiliations
- Global Health Educators Community
- American Society for Nutrition
- American Association for the Advancement of Science
- International Society for Evolution, Medicine, and Public Health
- American Association of Biological Anthropologists
- Human Biology Association
Media Appearances
Can You Change Your Metabolism?
Scientific American online
2023-06-14
Basal, or resting, metabolic rate refers to work performed by cells when we are doing nothing. It’s the baseline hum of being alive as cells keep blood circulating and lungs functioning. Formally, it’s the calories per minute used for these housekeeping duties. That adds up to about 50 to 70 percent of the total you burn through each day, depending on age, says Samuel Urlacher, an anthropologist and human evolutionary biologist at Baylor University in Waco, Tex.
Exercise vs. Diet? What Children of the Amazon Can Teach Us About Weight Gain
The New York Times online
2021-02-24
ut which of those concerns might be more important — inactivity or overeating — remains murky and matters, as obesity researchers point out, because we cannot effectively respond to a health crisis unless we know its causes.
That question drew the interest of Sam Urlacher, an assistant professor of anthropology at Baylor University in Waco, Texas, who for some time has been working among and studying the Shuar people.
Why do kids have more energy than adults?
Brain On! Podcast online
2020-06-30
We’re taking on an age-old question today: Do kids have more energy than adults? Breakfast tacos, caffeine, an energized DJ and an epic battle between a girl and her parents. This episode has all that and then some. Discover how we turn food into energy at an awesome taco party. Then pump up the jams with DJ Thyroid. Speaking of music, get ready for a song from Lake Street Dive’s Mike Olson. And just when you think the show might be out of energy, we engage in an out-of breath competition between a kid and her parents. Plus, there’s a brand new Mystery Sound and a Moment of Um about why we lose our voices sometimes.
Research Grants
Children’s third-party intervention across urban and rural contexts
CIFAR, Catalyst Grant
2023-2025
Follow-Up of the Waco COVID Survey
Baylor University, University Research Committee Award
2025
A biocultural evolutionary investigation of childhood intestinal energy absorption in the context of poor sanitation
National Science Foundation, Doctoral Dissertation Research Improvement Grant
2025-2026
Articles
Circulating Epstein–Barr Virus Antibody Levels as a Biomarker of Socioecological Adversity in Amazonian Ecuador
American Journal of Human Biology2025
Objectives
Circulating Epstein–Barr virus antibodies (EBV‐Ab) are used as a biomarker of chronic stress in high‐income settings, but their relevance in environments with a high burden of infectious disease, nutritional constraints, and limited resources is less clear. We investigated EBV‐Ab as a biomarker of adversity in a setting where local ecology and economy may affect immune development differently than in wealthy countries.
Soil‐Transmitted Helminths and the Intricacies of Immunoregulation: Evidence From Amazonian Ecuador for the Importance of Considering Species‐Specific Effects Within the Old …
American Journal of Human Biology2025
Objectives
The old friends hypothesis (OFH) examines connections between the global increase in immunoregulatory diseases (e.g., allergy and autoimmunity) and reduced exposure to immune‐priming symbionts like soil‐transmitted helminths. Helminth species, however, vary in their effects on hosts and should be considered separately. We examined relationships between species‐specific helminth infection and circulating biomarkers of adaptive immune antibodies (total immunoglobulin E [IgE]), systemic inflammation (C‐reactive protein [CRP]), and immune regulation (interleukin‐6 [IL‐6]), among Indigenous Shuar adults. We predicted that STH infection would be (1) associated with higher levels of IgE and (2) lower levels of CRP, with (3) IL‐6 driving these associations based on species‐specific relationships.
Salivary Testosterone, Age, and Adiposity Associations Among Shuar Males in Amazonian Ecuador Challenge Assumptions of “Normal” Testosterone Patterns
American Journal of Human Biology2025
Objectives
Adult male testosterone concentrations in high income countries often decrease with age and adiposity, a pattern typically viewed as “normal.” However, testosterone is expected to be adaptively regulated within the range of resource constrained, high pathogen, natural fertility conditions across which it evolved to function. We therefore examine associations among testosterone diurnal variation, age, and adiposity among Indigenous Shuar males of Amazonian Ecuador.
Validation of an Enzyme‐Linked Immunosorbent Assay for Measuring Leptin, a Key Metabolic Hormone, in Dried Blood Spot Samples
American Journal of Human Biology2025
Objectives
Leptin is an established biomarker of appetite regulation and energy status. Problematically, heavy reliance on invasive venipuncture sampling has limited leptin research with diverse human populations and groups such as children. Key questions remain about leptin's evolution and biological roles across the full range of humans. Here, we present and validate a new minimally invasive approach for measuring leptin in finger‐prick dried blood spots (DBS) using a commercial ELISA kit.
Sex Differences in Measures of Energy Expenditure and Body Composition in Young, Middle-Aged, and Older Adults
Current Developments in Nutrition2025
Background
Total daily energy expenditure (TDEE) is vital for energy balance and cardiometabolic health, yet its trajectory across the lifespan, particularly in women, remains poorly understood.
Objective
We sought to examine the effects of aging and sex on body composition and TDEE.
The energetics of childhood: Current knowledge and insights into human variation, evolution, and health
Yearbook of Biological Anthropology2023
How organisms capture and ultimately use metabolic energy–a limiting resource of life–has profound implications for understanding evolutionary legacies and current patterns of phenotypic variation, adaptation, and health. Energetics research among humans has a rich history in biological anthropology and beyond. The energetics of childhood, however, remains relatively underexplored. This shortcoming is notable given the accepted importance of childhood in the evolution of the unique human life history pattern as well as the known sensitivity of childhood development to local environments and lived experiences.
Childhood Daily Energy Expenditure Does Not Decrease with Market Integration and Is Not Related to Adiposity in Amazonia
The Journal of Nutrition2021
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 diet and energy expenditure on the development of OW/OB in transitioning contexts.
Daily energy expenditure through the human life course
Science2021
Total daily energy expenditure (“total expenditure”) reflects daily energy needs and is a critical variable in human health and physiology, but its trajectory over the life course is poorly studied. We analyzed a large, diverse database of total expenditure measured by the doubly labeled water method for males and females aged 8 days to 95 years. Total expenditure increased with fat-free mass in a power-law manner, with four distinct life stages. Fat-free mass–adjusted expenditure accelerates rapidly in neonates to ~50% above adult values at ~1 year; declines slowly to adult levels by ~20 years; remains stable in adulthood (20 to 60 years), even during pregnancy; then declines in older adults. These changes shed light on human development and aging and should help shape nutrition and health strategies across the life span.
Constraint and trade-offs regulate energy expenditure during childhood
Science Advances2019
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 that Shuar forager-horticulturalist children of Amazonian Ecuador are ~25% more physically active and, in association with immune activity, have ~20% greater resting energy expenditure than children from industrial populations. Despite these differences, Shuar children’s total daily energy expenditure, measured using doubly labeled water, is indistinguishable from industrialized counterparts. Trade-offs in energy allocation between competing physiological tasks, within a constrained energy budget, appear to shape childhood phenotypic variation (e.g., patterns of growth). These trade-offs may contribute to the lifetime obesity and metabolic health disparities that emerge during rapid economic development.
Tradeoffs between immune function and childhood growth among Amazonian forager-horticulturalists
Proceedings of the National Academy of Sciences2018
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 reserves) protect children from the particularly detrimental impact of acute inflammation on growth. These findings provide evidence for considerable energetic tradeoffs between immune function and growth among humans, highlighting the energy constraint of childhood and the characteristic ability of our species to respond sensitively to dynamic environmental conditions. We outline the possible role of immune-related tradeoffs in driving patterns of human growth faltering, developmental metabolic plasticity, and life history evolution.
