Original Research Article
Barrier requirements as the evolutionary “driver” of epidermal pigmentation in humans
Article first published online: 5 MAR 2010
Copyright © 2010 Wiley-Liss, Inc.
American Journal of Human Biology
Volume 22, Issue 4, pages 526–537, July/August 2010
How to Cite
Elias, P. M., Menon, G., Wetzel, B. K. and Williams, J. W. (2010), Barrier requirements as the evolutionary “driver” of epidermal pigmentation in humans. Am. J. Hum. Biol., 22: 526–537. doi: 10.1002/ajhb.21043
- Issue published online: 1 JUN 2010
- Article first published online: 5 MAR 2010
- Manuscript Accepted: 3 JAN 2010
- Manuscript Revised: 28 DEC 2009
- Manuscript Received: 21 AUG 2009
- NIH. Grant Numbers: AR019098, AI059311
- Medical Research Service, Department of Veterans Affairs, San Francisco, CA
Current explanations for the development of epidermal pigmentation during human evolution are not tenable as stand-alone hypotheses. Accordingly, we assessed instead whether xeric- and UV-B-induced stress to the epidermal permeability barrier, critical to survival in a terrestrial environment, could have “driven” the development of epidermal pigmentation. (1) Megadroughts prevailed in central Africa when hominids expanded into open savannahs [≈1.5–0.8 million years ago], resulting in sustained exposure to both extreme aridity and erythemogenic UV-B, correlating with genetic evidence that pigment developed ≈1.2 million years ago. (2) Pigmented skin is endowed with enhanced permeability barrier function, stratum corneum integrity/cohesion, and a reduced susceptibility to infections. The enhanced function of pigmented skin can be attributed to the lower pH of the outer epidermis, likely due to the persistence of (more-acidic) melanosomes into the outer epidermis, as well as the conservation of genes associated with eumelanin synthesis and melanosome acidification (e.g., TYR, OCA2 [p protein], SLC24A5, SLC45A2, MATP) in pigmented populations. Five keratinocyte-derived signals (stem cell factorKIT; FOXn1FGF2; IL-1α, NGF, and p53) are potential candidates to have stimulated the sequential development of epidermal pigmentation in response to stress to the barrier. We summarize evidence here that epidermal interfollicular pigmentation in early hominids likely evolved in response to stress to the permeability barrier. Am. J. Hum. Biol., 2010. © 2010 Wiley-Liss, Inc.