Publication Date

Summer 7-12-2019

Abstract

Fluctuating asymmetry (FA), characterized by random left-right deviations from perfect symmetry in anatomical structures, is a form of bilateral asymmetry that is thought to reflect underlying developmental instability (DI). DI refers to an organism’s relative ability to buffer against stochastic fluctuations in environmental conditions throughout development. FA is commonly used within evolutionary biology and anthropology as a cumulative indicator of chronic stress exposure during development and its consequences for long-term health. While the FA literature is extensive, there are two primary areas of inquiry that remain incomplete: assessing the full breadth of health correlates of FA across the human life course and investigating the specific environmental conditions during development that promote FA in humans.

This dissertation examines the role of facial FA as a bidirectional indicator of early-life stress and its later-life health consequences among contemporary New Mexicans. As part of the broader Heritage New Mexico study, in a series of three individual research chapters, we explored the following: 1) the relationship between FA and individual biomarkers of disease risk, interpreted under the lens of the Developmental Origins of Health and Disease (DOHaD) hypothesis; 2) the link between FA and allostatic load, as two complementary indicators of cumulative stress experiences; and 3) a broad range of environmental influences during development, encompassing the physical and sociocultural environment, that contribute to FA variation in adulthood. Data included three-dimensional facial photographs, a series of 10 biomarkers of degenerative disease risk and outcomes, current sociodemographic information, and a retrospective questionnaire addressing various aspects of the developmental environment.

We found that facial FA predicts only one biomarker of degenerative disease risk, systolic blood pressure, and its predictive utility varied by age and sex; facial FA was positively associated with systolic blood pressure among middle and older adult women only. While this finding is consistent with predictions from the DOHaD hypothesis, these results suggest that FA may not be particularly informative for understanding disease risk variation in our sample. Similarly, we found no association between FA and two allostatic load indices representing cumulative disease burden. However, we found a significant negative association between childhood dietary quality and facial FA in adulthood, while controlling for socioeconomic status (in childhood and adulthood), a rural childhood home environment, and childhood sickness. This pattern of results across chapters suggests that, in our sample, facial FA carries a developmental signal of dietary quality, but this variation does not necessarily translate to a range of diet-mediated disease risks in adulthood. This research represents an important step in broadening our understanding of the range of health correlates of facial FA, as well as the environmental conditions during development that contribute to variation in facial FA in adult humans. Since FA can be measured from soft and bony tissues, in the living and the dead, these findings within a living human sample serve to illuminate the utility of FA as a cumulative marker of stress and health among past populations.

Keywords

growth and development, health outcomes, disease, evolutionary biology

Document Type

Dissertation

Language

English

Degree Name

Evolutionary Anthropology

Level of Degree

Doctoral

Department Name

Anthropology

First Committee Member (Chair)

Heather J. H. Edgar

Second Committee Member

Keith L. Hunley

Third Committee Member

Melissa Emery-Thompson

Fourth Committee Member

Steven Gangestad

Fifth Committee Member

Nathan Young

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