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Hair and the course of human history

Yale Medicine Magazine, 2016 - Spring


The hair on our heads is just the departure point for this wide-ranging book by Kurt Stenn, M.D. The former Yale pathologist and dermatologist moves from the evolution of human hair to hair’s effects on culture, psychology, and global trade. By the end of Hair: A Human History, a reader might even be convinced that hair makes the world go ’round.

Stenn begins by explaining why we, of all primates, lost most of our body hair: Our ancestors became naked apes to cool their growing and temperature-sensitive brains, which would suffer a meltdown (that is, brain death) at 107 degrees Fahrenheit. Just 10 or 20 minutes of walking, scientists have estimated, would have felled upright fur-covered hominids with heatstroke.

Unlike animal hair, which grows on a fixed cycle and sheds twice a year, human hair follicles stagger their growth. Moreover, each type of human hair abides by its own calendar. A scalp hair shaft will grow for two to six years, allowing humans to wear hair cascading down their backs or in coronas around their heads. Eyelashes remain short because they grow for just 30 days.

Another mammal’s hair—sheep’s wool—shaped Western culture. English herders raised the best wool, and competed with Flanders to turn it into cloth for the world. The wool trade created the fortunes of such bankers as the Florentines, whose patronage of Michelangelo gave us the Sistine Chapel’s painted ceiling. The descendant of an English wool merchant named John Barton placed a sign in the window of his “fair stone house” that exulted, “I thank God and ever shall/It is the sheepe hath payed for all.”

The hair of the beaver also changed the course of history. By the 16th century, beaver-felt hats were all the rage in Europe. Hatters who used toxic mercury in the felting process developed dementia—thus, the expression “mad as a hatter.” Nonetheless, “everyone who was anyone” wanted a beaver hat, Stenn writes. When the fashion killed off beavers in European forests, traders sailed to North America, where Native Americans bartered pelts for pots, guns, rum, and metal beaver traps. By about 1840, the trade had ravaged the North American beaver population as well.

Animal hair does more than keep us warm and stylish. Bow makers, called archetiers, use horsehair and rosin to create the ribbon on a violin or cello bow. (Stallions from cold climates provide the best bow hair.) Percussionists strike drums using hammers cushioned with sheep’s wool felt. Paintbrushes contain hair from pigs, squirrels, badgers, and cows.

Research into hair could help solve fundamental scientific problems, Stenn says. For instance, scientists do not fully understand what causes stem cells in the mid-follicle to differentiate into hair shaft cells. “If we understood the hair follicle,” says Stenn, “we would probably get a good understanding of the regeneration process of the lung and the kidney and the eye. Biology is so conserved that the law of one organ system is very related to the law of another system.”

During two years of research, Stenn visited wigmakers in Japan, studied the anthropology of hair in Paris, learned about furs in Montreal, and toured a wool museum in Wales. Stenn, on the faculty at the School of Medicine from 1971 to 1991 and the former director of skin biology at Johnson & Johnson, now writes full time. Next, he plans an illustrated children’s book on hair. “I’ll still keep the science in,” says Stenn. He may use dogs and cats to demonstrate that fur is directional. “You don’t pet your cat from tail to head.”

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