Integrative Primate Research Lab
An anthropology lab that integrates behavioral and contextual data with skeletal studies to reveal how within-sex variation evolves and develops in our closest living relatives
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What if evolutions most revealing secrets are not between males and females but within them?
What if evolutions most revealing secrets are not between males and females but within them?
About the Lab
About the Lab
Biological anthropology seeks to understand what it means to be human by studying our closest living relatives and the deep history of our species. Much research has focused on differences between males and females, yet enormous variation within those categories remains poorly understood.
The Integrative Primate Research (IPR) Lab's research investigates how this within-sex variation arises using a holistic approach that integrates skeletal analysis with behavioral observations in the field and historical and contextual analyses. We explore how evolution and development shape variation within a species. Our work primarily focuses on orangutans as they exhibit an extreme form of within sex variation.
We take a reflexive and theoretically engaged approach, examining primate biology while considering how our own perspectives shape the questions we ask about evolution and the kinds of variation we recognize in nature.
Research Questions
Research Questions
How does a striking form of within-male variation in orangutans develop?
How does a striking form of within-male variation in orangutans develop?
In orangutans, adult males can mature along two distinct paths: some develop cheek pads and throat pouches, while others remain unflanged for years—or even for life. This project investigates the skeletal and behavioral signatures of these alternative forms of adulthood, revealing how growth and development create multiple ways of being male.
Dr. Kralick's work has shown that adult unflanged males are not ‘female-sized' but exhibit a range of body sizes that can overlap with both adult flanged males and adult females (Kralick, 2023, Integrative and Comparative Biology) and exhibit intermediate leg-to-arm bone strength ratios (Kralick et al., 2024, Journal of Human Evolution). Dr. Kralick has found that adult unflanged males experienced less severe early life stress when compared to flanged males (Kralick and McGrath, 2020, 2021, American Journal of Physical Anthropology).
Going forward, the IPR Lab will examine the relationship between flanging, heredity, and stress using a global database of zoo records co-lead with Dr. Stephanie Canington (see Fachnie et al., 2024; Hurlbut et al., 2025).
Future work is examining how the skeletons of unflanged males develop, and how they differ from those of flanged males.
Can variation among male orangutans help us separate out traits typically associated with only one sex?
Can variation among male orangutans help us separate out traits typically associated with only one sex?
In most primates, smaller body size and infant-carrying co-occur in females, blurring our ability to tell which influences movement more. Orangutans offer a unique opportunity to separate the two as unflanged males can be smaller than flanged males but do not carry offspring.
A new Leakey-funded project with the Tuanan Orangutan Research Station in Borneo, Indonesia will be comparing how these unflanged males and adult females move to disentangle how infant care vs body size impact movement patterns and refine our understanding of how evolution shapes diversity within and across sexes.
What is revealed about variation when we look at the whole skeleton in context and connect it to historical data, archival data, and behavior?
What is revealed about variation when we look at the whole skeleton in context and connect it to historical data, archival data, and behavior?
When we reunite the whole skeleton with its story, we see individuals rather than collections of parts. By connecting bones with field notes, archival records, and observed behavior, we reveal patterns of variation and the colonial histories that shaped how these specimens came to be in museums. This holistic view allows us to ask more nuanced evolutionary questions and build a fairer science, one that organizes scattered collections, elevates local knowledge, and recognizes orangutan remains as complete beings. That’s the purpose of the Global Whole Ape Curation Project, supported by the Wenner-Gren Global Initiatives Grant: context that unlocks discovery.
Publications
Publications
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