Variation of Human Hairiness: A Possible Adaptation to Solar Radiation and Melanin

Amrita Dhugga; Maciej Henneberg; Jaliya Kumaratilake

doi:10.2478/anre-2014-0017

Authors

Amrita Dhugga Level 1 University of Adelaide Medical School North, Adelaide 5005, SA
Maciej Henneberg Biological Anthropology and Comparative Anatomy Unit, The University of Adelaide
Jaliya Kumaratilake Biological Anthropology and Comparative Anatomy Unit, The University of Adelaide

DOI:

https://doi.org/10.2478/anre-2014-0017

Keywords:

evolution of hair, Von Luschan’s Scale, skin colour reflectance, hairiness

Abstract

Many theories have been advanced to explain human hairlessness, however, there is no consensus. This study of 76 males observed that skin reflectance measuring skin colouration and melanin pigmentation correlated with hair size and follicle density. Individuals with a greater concentration of melanin within the superficial layer of the skin had a lower follicle density and smaller sizes of hairs. In contrast, individuals with a lower melanin concentration and lighter skin colour had a full range of hairiness. This leads to the suggestion that over the course of human evolution, high concentrations of melanin in consistently exposed to ultraviolet radiation areas developed first and that hair loss was a consequence of competition in the skin between melanin production and hair growth. Darker pigmented skin and lower follicle density are significantly correlated (R2=0.283; p<0.05). Individuals with darker skin had a mean of 4.91 follicles per cm2 whereas those with lighter skin reflectance had 11.20 follicles per cm2. This suggests that increased concentrations of melanin in the basal layer of the epidermis may limit hairiness by negatively influencing the skin’s ability to produce hair.

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