“Beards, Baldness, and Sweat Secretion,” Michel Cabanac and H. Brinnel, European Journal of Applied Physiology and Occupational Physiology, vol. 58, nos. 1–2, 1988, pp. 39–46. The authors, who are at Université Laval, Quebec, Canada, explain that [AIR 16:1]:
“In 100 clean-shaven men direct measurement of the area of glabrous [in plain language: bald] skin on the forehead and calvaria was found to be proportional to that of the hairy skin on the lips, cheeks, chin and
neck…. [Our] results support the hypothesis that male baldness is a thermoregulatory compensation for the growth of a beard in adults.”