The Dark Side of the Sun

Natural History, July, 2001 by Ellen Goldensohn

At some point in the recent history of our species, people of European descent began to cultivate the suntanned look. (Notions of physical beauty are often tied to symbols of prosperity and leisure. A suntan--which once signaled long hours of working outdoors--became in the twentieth century a conspicuous advertisement that one had nothing more pressing to do than travel to a seacoast and lie about on a beach blanket.)

Biologically, suntans--and dark-pigmented skin in general--tell another, more objective story: that human beings have an ambivalent evolutionary relationship with the sun. Yes, our star is the source of all life and energy, yet we can never look straight at it, and overexposure to its radiation can be fatal. Other animals, as well as plants and protists and bacteria, have the same paradoxical involvement with the sun. That's why hammerhead sharks get suntans, why some sea urchins eat algae, and why certain grasses produce chemical sunscreens.

Back in 1985, the British Antarctic Survey announced that the ozone layer was thinning and that living things were being exposed to elevated levels of ultraviolet radiation--the form of sunlight with the greatest potential to cause biological harm. Getting a suntan, like cigarette smoking several decades earlier, dropped from the list of life's harmless pleasures.

Science writer Jay Withgott ("Feeling the Burn," page 38) reports on biological research that has followed the discovery of the ozone hole, relaying the sometimes reassuring, sometimes alarming findings. If you happen to read this article while vacationing at the beach, please move into the shade.