Skin: A Natural History

Skin: A Natural History, by Nina G. Jablonski
reviewed by Rosemarie L. Coste

I think a good non-fiction book should answer some questions and suggest other questions, so that the result of reading the book is not to feel that the problem is solved but that the investigation can now advance to a higher, more interesting, level. Skin (University of California Press, 2006) met that requirement for me: having read it, I do have a broader general understanding of skin (thanks in part to the author’s willingness, in a book written for non-scientists, to use and explain scientific vocabulary) but I am left wondering about the many unanswered questions that occurred to me while I was reading it.

One of the questions this book raised for me (probably midway through the chapter on “Sweat”) is about the book’s own subtitle, A Natural History. I have enjoyed visits to several museums of natural history, and I own several other books that call themselves natural histories of other subjects, but I had not, until I started wondering why some topics were discussed in Skin and others were omitted, wondered what specific promises are being made by naming any collection of information “a natural history.”

As it turns out, labeling anything “natural history” is a good way to announce that its contents can’t be predicted. A natural history can be the sum of all facts related to a subject, or a non-systematic study relying on field observation rather than laboratory investigation, or a genre of scientific material addressed to a non-scientific readership, or the work of an amateur scientist. The Wikipedia article on Natural History is worth reading for its discussion of how the usage of the term has changed; the discussion page associated with the article is equally interesting, recording the in-progress struggle to create a clear explanation of an unclear idea.

The author of Skin, Nina G. Jablonski, is an anthropologist whose primary field of study is skin color. She begins the book by explaining that she had originally envisioned it to be focused on skin color, but was persuaded by her editor to expand its scope to discuss skin more broadly. Within limits she has done so, but skin color remains the major focus of the book.

Skin is organized into eleven chapters, preceded by a list of illustrations and followed by a valuable glossary, notes, a list of references that will make further reading more productive, and an index. The chapters are:

  1. Skin Laid Bare
    This introductory chapter, with clear drawings of the multi-layered structure of skin, is as far as most general-readership discussions of the subject attempt to go. Instead of being the destination, the vocabulary and concepts introduced here are the foundation for the remainder of the book.
  2. History
    A key question is introduced here: since skin, unlike bones, does not leave much evidence in the fossil record, how is it possible for anyone to know how skin has changed in the course of human evolution? For this purpose, Jablonski points to three characteristics shared by all primates, human and non-human, and presumably by their common ancestor: primate skin is thicker in back than in front, and most of it is covered with hair; primate skin can produce sweat; primate skin contains melanin. Most non-human primates are born with dark hair and light skin; the skin of less-hairy areas darkens when exposed to sunlight, so infant primates have light-colored faces and hands while adults typically have dark skin in those exposed areas. Adult captive animals which seldom see the sunlight retain the light faces of infants, showing that the skin’s color change relates to light exposure, not to the aging process (unlike the greying of hair, which happens whether or not the animal is exposed to sunlight).
  3. Sweat
    Human bodies are not hairless; we have just as many hair follicles, distributed in the same way, as other primates. The hairs themselves, though, are thin and short, allowing humans to cool more efficiently through the evaporation of sweat from exposed skin. This chapter explores the features of our skin that help us keep cool, including our unique reliance on rapidly-evaporating eccrine sweat (thin, watery, produced in copious amounts) rather than lathery apocrine sweat (milky, viscous, remaining as a coating on the body) as other mammals do.
  4. Skin and Sun
  5. Skin’s Dark Secret
  6. Color
    These three chapters explore Jablonski’s fascination with skin color and the ways in which humans have adapted to balance competing needs for dark skin, which protects itself and the interior of the body from sun damage, and light skin, which supports the body’s ability to produce Vitamin D in sunlight.
  7. Touch
    In this chapter, Jablonski explores the sense of touch, mediated by the skin, as an influence in human evolution and social development. Nails are also part of this discussion: primates have nails, protecting only the tops of fingers and toes, rather than claws like other climbing animals, giving us improved sensitivity in our fingers and toes while trading off some of our ability to fight.
  8. Emotions, Sex, and Skin
    This eight-page chapter seems unfinished. It revisits some of the ideas raised in other chapters (particularly about sweat, touch, and color) but does not use them to create an organized discussion of the topics identified in the chapter title.
  9. Wear and Tear
    Subsections of this chapter are devoted to some of the many things that can go wrong with skin: Birthmarks and Moles; Scabs; Scars; Bites and Stings; Burns; Dermatitis; Pimples and Acne; Warts; Stretch Marks; Rosacea; Wrinkles; Shingles; Skin Cancers. With so many problems listed, only very general information can be provided about each one.
  10. Statements
  11. Future Skin
    These final chapters, like the chapter on “Emotions, Sex, and Skin”, relate largely to how skin has been or can be used for social, artistic, and communicative purposes. Much of the “Statements” chapter returns to the theme of skin color, discussing how different cultures at different times have valued light skin or dark skin, often both for the same reason that the favored color is seen as a sign of youth, health, and wealth. In “Future Skin”, Jablonski identifies three frontiers along which “the functions and potential of skin will be expanded” in decades to come: improvements of skin’s ability to repair itself after injury or disease; expanded communicative and sensory options through cosmetics and technological implants; creation of skin for robots, allowing them to simulate human touch.

Skin is thoroughly illustrated with photographs and drawings; most are in black-and-white, but there is a section of color plates. My favorite of the color photos is a close-up of a hippopotamus’ face, showing the “red sweat” it secretes as a sunscreen.

Because Jablonski is an anthropologist and I am not, I was curious about how closely her ideas reflect mainstream thought among scientists who study humans. Specifically, I wonder how much support there is for her explanations of how the variation in human skin colors evolved, and how skin color relates to gender roles. For some insight into this, read Dunsworth’s review of Skin in PaleoAnthropology, the online journal of the Paleoanthropology Society.

Skin is not about recommending which lotions and creams to apply to skin, nor about how to correct skin problems such as those associated with age (wrinkles) and youth (acne). It’s about skin as a physical object: what it’s made of, how it works, how it has changed, and how we know. It asks and answers some valid questions. It leaves many other questions unanswered.