Hair fiber morphology and function: at the intersection of anthropology, physiology, and engineering

Abstract

Humans are unique among mammals in having a nearly naked body but a fur‐covered head. Furthermore, scalp hair is one of the most variable traits among human populations. However, the evolutionary emergence of scalp hair, the factors contributing to its evolution, and its subsequent diversification remain largely unknown. Among the few discussions of human scalp hair evolution is the hypothesis that hairy scalps may have evolved as protective barriers against solar radiation in bipedal savannah dwellers. Managing thermal load would be particularly important in the context of a large thermogenic and thermosensitive brain. And as the presence and morphology of fur, or hair, is generally of great importance to mammalian thermoregulation, we set out to test the thermal effect of scalp hair (morphology). To do this, we developed methods for the quantification of hair fiber morphology and experimentally tested the effect of scalp hair (and variation in its morphology) on heat gain from solar radiation. Thermal manikins are human models designed for scientific testing of thermal environments and to simulate heat transfer between the skin and the environment in a range of temperatures. Using one such thermal manikin, we collected data on heat flux when the manikin was equipped with no wig, and wigs of various hair textures. Our preliminary results show that tightly curled scalp hair, in particular, minimizes the heat gained from solar radiation (Figure 1). The study is being expanded and experiments repeated to enable statistical testing. We plan to use these data in mathematical models of human physiological response to estimate the impact scalp hair might have had in early human evolution. In this research we combined anthropological theory, physiological models and engineering methods to answer a longstanding question of human evolution ‐ why did humans evolve scalp hair and why does it vary? The innovative work stemming from this collaboration provided the opportunity to tackle old questions in new ways and pave the way for more potential interdisciplinary work.Support or Funding InformationThis work is supported by the National Science Foundation (award number 1847845); the Wenner‐Gren Foundation (grant number 9911); and the Africana Research Center at The Pennsylvania State University.Solar heat gain in different hair textures at three windspeeds.Figure 1