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J Hum Evol. 2018 Dec;125:99-105. doi: 10.1016/j.jhevol.2018.10.008. Epub 2018 Nov 7.

Comparative evidence for the independent evolution of hair and sweat gland traits in primates.

Author information

1
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA. Electronic address: yana2@pennmedicine.upenn.edu.
2
Department of Genetics, Harvard Medical School, Boston, MA 02115, USA.
3
Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
4
Department of Dermatology, Cutaneous Biology Research Center, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA 02129, USA.
5
FAS Center for Systems Biology, Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA; The Broad Institute of MIT and Harvard, Cambridge, MA 02142, USA; Howard Hughes Medical Institute, Chevy Chase, MD 20815, USA; Department of Immunology and Infectious Disease, Harvard T.H. Chan School of Public Health, Boston, MA 02115, USA.
6
Department of Human Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA. Electronic address: danlieb@fas.harvard.edu.

Abstract

Humans differ in many respects from other primates, but perhaps no derived human feature is more striking than our naked skin. Long purported to be adaptive, humans' unique external appearance is characterized by changes in both the patterning of hair follicles and eccrine sweat glands, producing decreased hair cover and increased sweat gland density. Despite the conspicuousness of these features and their potential evolutionary importance, there is a lack of clarity regarding how they evolved within the primate lineage. We thus collected and quantified the density of hair follicles and eccrine sweat glands from five regions of the skin in three species of primates: macaque, chimpanzee and human. Although human hair cover is greatly attenuated relative to that of our close relatives, we find that humans have a chimpanzee-like hair density that is significantly lower than that of macaques. In contrast, eccrine gland density is on average 10-fold higher in humans compared to chimpanzees and macaques, whose density is strikingly similar. Our findings suggest that a decrease in hair density in the ancestors of humans and apes was followed by an increase in eccrine gland density and a reduction in fur cover in humans. This work answers long-standing questions about the traits that make human skin unique and substantiates a model in which the evolution of expanded eccrine gland density was exclusive to the human lineage.

KEYWORDS:

Eccrine gland; Ectodermal appendage; Hair; Human evolution; Skin; Sweat gland

PMID:
30502901
PMCID:
PMC6289065
DOI:
10.1016/j.jhevol.2018.10.008
[Indexed for MEDLINE]
Free PMC Article

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