The Wild File


Q) Is human skin waterproof and breathable?
Mike Callaghan, Toronto, Ontario

IN OTHER WORDS, is your skin like a naturally occurring Gore-Tex jacket? The answer, according to Dr. Robert Polisky, a dermatologist in Elk Grove Village, Illinois, is both yes and no. Skin, which protects the body against injury, microorganisms, and chemical agents, is water-resistant but not waterproof. The protective layer is called the stratum corneum, a thin membrane of mostly dead cells that's rich in a protein called keratin and also coated with sebum, an oil secreted through hair follicles. Together they create a water-resistant barrier that protects the dermis, where the capillaries and sweat glands lie. (If you want to verify that your skin isn't waterproof, take a long bath—the prunelike effect on your hands and feet is a result of the keratin becoming waterlogged.) So does your skin breathe? Not in a strict sense: Your pores don't inhale or exhale. But they do allow harmful metabolic wastes like salt and urea to escape the body when it heats up. Thus, the skin, which weighs an average of 6.5 pounds, may be heavier than a high-performance jacket, but it has at least one distinct advantage: You never need to take it to the dry cleaner.

Q) When birds swoop around en masse, how do they decide who does the steering?
Virginia Grabow, Tigard, Oregon

YOU'VE OPENED a big can of worms, and we don't mean the kind that our flying friends like to feast on. While many animal groups—packs of wolves, for example—travel under the guidance of a dominant leader, it appears that with large flocks of birds, such as those 200 starlings you might see carousing around your neighborhood, there is no leader of the pack. So what's going on? That's what California computer scientist Craig Reynolds wanted to know. "I used to go out in my backyard and watch the flocks and wonder how in the world they worked," he says. So in 1986 he set out to crack the case by creating a virtual-bird program that he dubbed Boids. Reynolds theorized that all birds follow a few specific rules, such as trying to fly as close together as possible without colliding and trying to maintain the same speed and direction. When he programmed the computer to reflect these rules and hit return, sure enough, the digital birds coalesced and flew in unison. He found that the "boid" out in front might lead the flock in one direction but then initiate a change that would result in another boid becoming the momentary "leader," with no single member doing all the steering. Ornithologists haven't proven that Reynolds's program precisely mirrors flocking behavior, but his is the prevailing theory for explaining this "emergent system"—a term chaos theorists use to describe a system in which order emerges from the behavior of simple parts. Sounds like something Congress should look into.

Q) Is the phrase "drink like a fish" a misnomer?
Guillermo Enriquez, Tempe, Arizona

THAT DEPENDS ON your definition of "drink." As Professor Richard Strange, of the University of Tennessee's Department of Forestry, Wildlife and Fisheries, explains, a fish's hydration depends chiefly on osmosis, which occurs whenever the concentration of salt in the water is lower on one side of a semipermeable membrane than on the other. In fish, this fluid exchange happens mostly through cell walls in the gills. Saltwater fish, poor things, have an unquenchable thirst, because they are constantly being dehydrated by the saltier sea all around them. Thus, their lives depend on the additional water content in the critters they eat, and the water they gulp down with them. (Most of the salt is filtered out in the kidneys.) Freshwater fish, being saltier than their environment, absorb water like a sponge, so they never have to "drink"—on the contrary, they urinate almost constantly. Which might explain those warm spots in the lake.

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