THE EVOLUTION OF HUMAN SKIN AND SKIN COLOR Nina G ...

More documents

Recommendations

Info

586 JABLONSKIcomparative anatomical and physiological evidence. Skin has also been overlookedas a topic of research interest in anthropology and human biology in recent decadesbecause of the social sensitivity surrounding discussions of skin color and becauseof the use and misuse of skin color in biological and social concepts of race.The goal of this review is to provide a comprehensive yet economical survey ofthe biology, evolution, and culture of human skin and skin color, with an emphasison new research—especially on the evolution of skin color. The review beginswith an overview of the basic biology of skin itself, followed by discussions of theevolution of skin and skin color, and of skin color and race.THE STRUCTURE AND FUNCTIONS OF HUMAN SKINThe skin serves as an effective physical barrier because its laminar structure rendersit relatively resistant to abrasion, puncture, and percutaneous absorption, andbecause its immune cells mount a first line of defense against pathogens comingin contact with the body. Lacking adequate protection from hair, human skin hasundergone numerous adaptive structural changes that give it strength, resilience,and sensitivity (Montagna 1981). The skin of humans, like that of all tetrapods,acts as a sun shield to protect the body from most solar UV radiation (UVR) andis the locus for the initiation of the important, UVR-driven process of vitamin Dproduction in the body.EpidermisThe laminar structure of human skin comprises two major tissue layers, a thinnerouter layer, the epidermis, and a thicker and more intemally complex inner layer,the dermis (Figure 1). Tbe epidermis is a stratified keratinizing epithelium witha smooth, abrasion-resistant surface that is interrupted only by hair follicles andthe pores of sweat glands. The barrier properties of the skin are predicated on theintegrity of the stratum comeum (Elias et al. 2003, Taylor 2002). Keratinocytes arethe principal cell type found in epidermis and are composed largely of filamentousproteins known as keratins, which are imbedded in an amorphous matrix. Theskin's elasticity and resistance to physical and chemical attack can be attributedto the high elastic modulus and unique amino acid composition of the keratinizedlayer of the epidermis (Marks 1991, Odiand 1991). The epidermis also containspopulations of three types of immigrant dendritic cells: melanocytes, Langerhanscells, and Merkel cells. Melanocytes produce the skin's primary pigment, melanin,and are discussed in greater detail below. Langerhans cells are specialized cellsof the immune system that present and respond to antigens coming in contactwith the skin, and Merkel cells are associated with nerve terminals that togetherfunction as slow-adapting mechanoreceptors for totich; they are most common onthe glabrous skin of tbe fingertips (Chu et al. 2003, Kripke & Applegate 1991,Lynn 1991, Odiand 1991). The epidermis is subdivided into four layers fromdeep to superficial; the stratum basale (the germinative layer of keratinocytesj, the
SKIN AND SKIN COLOR 587Melanocytes Keratinocytes Nerve endings FibroblastsFigure 1 Schematic rendering of a cross-section of human skin, showing itslaminar structure, main cell types, and appendages.
Page 1: Annu. Rev. Anthropol. 2004. 33:585-
Page 5 and 6: SKIN AND SKIN COLOR 589IStratum cor
Page 7 and 8: SKIN AND SKIN COLOR 591related to i
Page 9 and 10: SKIN AND SKIN COLOR 593visual redne
Page 11 and 12: •T>^SKIN AND SKIN COLOR 595functi
Page 13 and 14: SKIN AND SKIN COLOR 597Holick has r
Page 15 and 16: SKIN AND SKIN COLOR 599therefore, g
Page 17 and 18: SKIN AND SKIN COLOR 6011988, van de
Page 19 and 20: SKIN AND SKIN COLOR 603freezing con
Page 21 and 22: SKIN AND SKIN COLOR 605UVA UVB UVC3
Page 23 and 24: SKIN AND SKIN COLOR 607of the skin
Page 25 and 26: SKIN AND SKIN COLOR 609Strong natur
Page 27 and 28: SKIN AND SKIN COLOR 611In evolution
Page 29 and 30: SKIN AND SKIN COLOR 613synchronized
Page 31 and 32: SKIN AND SKIN COLOR 615Rogers et al
Page 33 and 34: SKIN AND SKIN COLOR 617Brace CL. 19
Page 35 and 36: SKIN AND SKIN COLOR 619Herman J, Ce
Page 37 and 38: SKIN AND SKIN COLOR 621Neer RM. 197
Page 39 and 40: SKIN AND SKIN COLOR 623Wassermann G

THE EVOLUTION OF HUMAN SKIN AND SKIN COLOR Nina G ...

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?