About

I am a human behavioral ecologist. Behavioral ecologists are interested in understanding the adaptive nature of behavior as a function of local socioecological context. My research focuses on a variety of questions related to family and romantic relationship dynamics. For the last 15 years I have co-directed the Kunene Rural Health and Demography Project in northwest Namibia, where our work has focused on understanding how family dynamics affect health and well-being. Increasingly, as the population I work with is undergoing rapid market integration, I am also interested in understanding how these changes affect access and use of the healthcare system, as well as beliefs and norms about birth and perinatal care.

Research topics

• Sociology
• Biology
• Political Science
• Social Science
• Psychology
• Geography
• Demography
• Engineering ethics
• Genetics
• Epistemology
• Ecology
• Zoology
• Environmental ethics
• Mathematics
• Social psychology
• Developmental psychology
• Law
• Criminology
• Biochemistry

Selected publications

• No evidence for disassortative mating based on HLA in a small-scale, endogamous population

  eLife · 2026-03-17

  articleOpen access

  Studies dating back several decades have suggested that humans prefer potential mates with dissimilar HLA genotypes. Evidence for actualized disassortative mating based on the human-specific MHC remains inconclusive. For instance, cosmopolitan populations have often exhibited the opposite trend whereby assortative mating at the MHC is observed, indicating that social stratification may overwhelm potential biological mate preferences. However, small-scale, endogamous populations–whose social structures more closely resemble those throughout most of human evolution–have been largely overlooked. Here, we assess HLA dissimilarity among Himba pastoralists from Namibia, where socially accepted concurrency allows individuals to maintain both arranged marital and self-selected (“love match”) partnerships. This provides a rare opportunity to directly test HLA similarity across contrasting partnership types (arranged vs chosen) within the same social system (n = 249 observed partnerships). We find no difference in HLA dissimilarity (neither at the genotype nor protein divergence level) between partnership types, nor in their fitness benefits to potential offspring as assessed via computationally predicted pathogen binding affinities. The effects of the partnership types likewise do not differ from a random, background distribution of 18,487 possible unrelated pairings. Finally, we detect extensive haplotype sharing across the HLA region, suggesting that episodes of fluctuating positive selection may be a stronger force maintaining HLA polymorphism than disassortative mating, even in an evolutionarily relevant social context.

  PublisherDOI

• Author Response: No evidence for disassortative mating based on HLA in a small-scale, endogamous population

  2026-03-17

  peer-reviewOpen access

  Studies dating back several decades have suggested that humans prefer potential mates with dissimilar HLA genotypes. Evidence for actualized disassortative mating based on the human-specific MHC remains inconclusive. For instance, cosmopolitan populations have often exhibited the opposite trend whereby assortative mating at the MHC is observed, indicating that social stratification may overwhelm potential biological mate preferences. However, small-scale, endogamous populations–whose social structures more closely resemble those throughout most of human evolution–have been largely overlooked. Here, we assess HLA dissimilarity among Himba pastoralists from Namibia, where socially accepted concurrency allows individuals to maintain both arranged marital and self-selected (“love match”) partnerships. This provides a rare opportunity to directly test HLA similarity across contrasting partnership types (arranged vs chosen) within the same social system (n = 249 observed partnerships). We find no difference in HLA dissimilarity (neither at the genotype nor protein divergence level) between partnership types, nor in their fitness benefits to potential offspring as assessed via computationally predicted pathogen binding affinities. The effects of the partnership types likewise do not differ from a random, background distribution of 18,487 possible unrelated pairings. Finally, we detect extensive haplotype sharing across the HLA region, suggesting that episodes of fluctuating positive selection may be a stronger force maintaining HLA polymorphism than disassortative mating, even in an evolutionarily relevant social context.

  PublisherDOI

• No evidence for disassortative mating based on HLA in a small-scale, endogamous population

  eLife · 2026-03-17

  articleOpen access

  Studies dating back several decades have suggested that humans prefer potential mates with dissimilar HLA genotypes. Evidence for actualized disassortative mating based on the human-specific MHC remains inconclusive. For instance, cosmopolitan populations have often exhibited the opposite trend whereby assortative mating at the MHC is observed, indicating that social stratification may overwhelm potential biological mate preferences. However, small-scale, endogamous populations–whose social structures more closely resemble those throughout most of human evolution–have been largely overlooked. Here, we assess HLA dissimilarity among Himba pastoralists from Namibia, where socially accepted concurrency allows individuals to maintain both arranged marital and self-selected (“love match”) partnerships. This provides a rare opportunity to directly test HLA similarity across contrasting partnership types (arranged vs chosen) within the same social system (n = 249 observed partnerships). We find no difference in HLA dissimilarity (neither at the genotype nor protein divergence level) between partnership types, nor in their fitness benefits to potential offspring as assessed via computationally predicted pathogen binding affinities. The effects of the partnership types likewise do not differ from a random, background distribution of 18,487 possible unrelated pairings. Finally, we detect extensive haplotype sharing across the HLA region, suggesting that episodes of fluctuating positive selection may be a stronger force maintaining HLA polymorphism than disassortative mating, even in an evolutionarily relevant social context.

  PublisherDOI

• A rapid accurate approach to inferring pedigrees in endogamous populations

  Genetics · 2025-05-20 · 4 citations

  articleOpen access

  Accurate reconstruction of pedigrees from genetic data remains a challenging problem. Many relationship categories (e.g. half-sibships vs avuncular) can be difficult to distinguish without external information. Pedigree inference algorithms are often trained on European-descent families in urban locations. Thus, existing methods tend to perform poorly in endogamous populations for which there may be reticulations within the pedigrees and elevated haplotype sharing. We present a simple, rapid algorithm which initially uses only high-confidence first-degree relationships to seed a machine learning step based on summary statistics of identity-by-descent sharing. One of these statistics, our "haplotype score," is novel and can be used to: (1) distinguish half-sibling pairs from avuncular or grandparent-grandchildren pairs; and (2) assign individuals to ancestor vs descendant generation. We test our approach in a sample of 700 individuals from northern Namibia, sampled from an endogamous population called the Himba. Due to a culture of concurrent relationships in the Himba, there is a high proportion of half-sibships. We accurately identify first through fourth-degree relationships and distinguish between various second-degree relationships: half-sibships, avuncular pairs, and grandparent-grandchildren. We further validate our approach in a second African-descent dataset, the Barbados Asthma Genetics Study, and a European-descent founder population from Quebec. Accurate reconstruction of relatives facilitates estimation of allele frequencies, tracing allele trajectories, improved phasing, heritability and other population genomic questions.

  PublisherOA PDFDOI

• The Role of Medical Mistrust in Vaccination Decisions in Rural, Indigenous Namibian Communities

  Journal of Racial and Ethnic Health Disparities · 2025-04-21 · 3 citations

  article
  PublisherDOI

• Common DNA sequence variation influences epigenetic aging in African populations

  Communications Biology · 2025-11-05 · 1 citations

  articleOpen access

  Aging is associated with genome-wide changes in DNA methylation in humans, facilitating the development of epigenetic age prediction models. However, these models have been trained primarily on European-ancestry individuals and none account for the impact of methylation quantitative trait loci (meQTL). To address these gaps, we analyze the relationships between age, genotype, and CpG methylation in 3 understudied populations: central African Baka (n = 35), southern African ‡Khomani San (n = 52), and southern African Himba (n = 51). We show that published prediction methods yield higher mean errors in these cohorts compared to European-ancestry individuals and find that unaccounted-for DNA sequence variation may be a significant factor underlying this loss of accuracy. We leverage information about the associations between DNA genotype and CpG methylation to develop an age predictor that is minimally influenced by meQTL and show that this model remains accurate across a broad range of genetic backgrounds. Intriguingly, we also find that the older individuals and those with lower epigenetic age acceleration carry more genetic variants linked to reduced epigenetic age. These findings support the hypothesis that multiple heritable factors collectively influence healthspan and longevity in human populations.

  PublisherOA PDFDOI

• Social learning is critical to breastfeeding success: Evidence from rural Namibian pastoralists

  Evolution Medicine and Public Health · 2025-01-01 · 1 citations

  articleOpen access1st authorCorresponding

  Background and objectives: Lactation is one of the defining features of mammals, yet many humans struggle with breastfeeding. One reason for this is that humans are unique among mammals in the degree of learning and support that they require to breastfeed successfully. Despite this, we know little about how social learning impacts breastfeeding, particularly outside the influence of biomedical systems. Methodology: Qualitative and systematic interviews were conducted with 128 Namibian women on infant feeding norms and practices. Structured statements were analyzed with cultural consensus analysis to determine whether a single cultural model exists and to identify variance in individual cultural competencies. Results: Cultural consensus analysis revealed a single cultural model for breastfeeding, with strong and consistent norms and a significant role for social learning. Both learning and instinct were invoked in women's responses, speaking to the necessary and expected role of intensive support in the early postpartum period. Women also noted steep learning curves and clear expectations about infant feeding, which led to nearly universal breastfeeding and clear paths for troubleshooting difficulties. Conclusions and implications: The breastfeeding support that Himba mothers receive is part of the legacy of assisted reproduction in humans. However, the features of intensive teaching and learning shown here are lacking in western models of infant feeding and postpartum care. These data suggest that protracted breastfeeding difficulties may result from a mismatch between the evolved socioecology of breastfeeding and current norms and practices that hinder social learning and impair support pathways.

  PublisherOA PDFDOI

• No evidence for disassortative mating based on HLA in a small-scale, endogamous population

  bioRxiv (Cold Spring Harbor Laboratory) · 2025-05-08

  preprintOpen access

  Studies dating back several decades have suggested that humans prefer potential mates with dissimilar HLA genotypes. Evidence for actualized disassortative mating based on the human-specific MHC remains inconclusive. For instance, cosmopolitan populations have often exhibited the opposite trend whereby assortative mating at the MHC is observed, indicating that social stratification may overwhelm potential biological mate preferences. However, small-scale, endogamous populations-whose social structures more closely resemble those throughout most of human evolution-have been largely overlooked. Here, we assess HLA dissimilarity among Himba pastoralists from Namibia, where socially accepted concurrency allows individuals to maintain both arranged marital and self-selected ("love match") partnerships. This provides a rare opportunity to directly test HLA similarity across contrasting partnership types (arranged vs chosen) within the same social system (n = 249 observed partnerships). We find no difference in HLA dissimilarity (neither at the genotype nor protein divergence level) between partnership types, nor in their fitness benefits to potential offspring as assessed via computationally predicted pathogen binding affinities. The effects of the partnership types likewise do not differ from a random, background distribution of 18,487 possible unrelated pairings. Finally, we detect extensive haplotype sharing across the HLA region, suggesting that episodes of fluctuating positive selection may be a stronger force maintaining HLA polymorphism than disassortative mating, even in an evolutionarily relevant social context.

  PublisherOA PDFDOI

• The cuckoldry conundrum

  Evolutionary Anthropology Issues News and Reviews · 2024-02-10 · 4 citations

  review1st authorCorresponding

  Concerns about cuckoldry are a dominant theme in evolutionary studies of mating, frequently used to explain sex differences in reproductive strategies. However, studies in nonhuman species have shown that cuckoldry can be associated with important benefits. These insights have not been well integrated with the human literature, which continues to focus on anticuckoldry tactics and negative repercussions for men. I evaluate two key assumptions central to human models of cuckoldry: (1) men are being tricked into investing in nonbiological offspring and (2) investment in nonbiological offspring is wasted. The ethnographic data on fatherhood shows that the concepts of pater and genitor are complex and locally constructed ideas that often include explicit knowledge of extra-pair paternity, countering the idea that nonpaternity results from trickery. Furthermore, rather than being a "waste," paternity loss can be associated with important gains for men, helping to explain why men invest in nonbiological offspring.

  PublisherDOI

• Women’s subsistence strategies predict fertility across cultures, but context matters

  Proceedings of the National Academy of Sciences · 2024-02-12 · 16 citations

  articleOpen access

  While it is commonly assumed that farmers have higher, and foragers lower, fertility compared to populations practicing other forms of subsistence, robust supportive evidence is lacking. We tested whether subsistence activities-incorporating market integration-are associated with fertility in 10,250 women from 27 small-scale societies and found considerable variation in fertility. This variation did not align with group-level subsistence typologies. Societies labeled as "farmers" did not have higher fertility than others, while "foragers" did not have lower fertility. However, at the individual level, we found strong evidence that fertility was positively associated with farming and moderate evidence of a negative relationship between foraging and fertility. Markers of market integration were strongly negatively correlated with fertility. Despite strong cross-cultural evidence, these relationships were not consistent in all populations, highlighting the importance of the socioecological context, which likely influences the diverse mechanisms driving the relationship between fertility and subsistence.

  PublisherOA PDFDOI

Recent grants

• A Bio-Cultural Study of Preferences, Behaviors, and Outcomes in Family Dynamics

  NSF · $416k · 2015–2021

Frequent coauthors

• Sean P. Prall

  University of Missouri

  32 shared

• Richard McElreath

  Max Planck Institute for Evolutionary Anthropology

  13 shared

• Monique Borgerhoff Mulder

  University of California, Davis

  13 shared

• Brenna M. Henn

  University of California, Davis

  12 shared

• Michael Gurven

  12 shared

• Jeremy Koster

  Max Planck Institute for Evolutionary Anthropology

  10 shared

• Mary K. Shenk

  10 shared

• Karen L. Kramer

  University of Utah

  10 shared

Labs

• KRHDPPI

  Not provided

Awards & honors

• Fulbright Award