The Wild File


Q) Do animals have a preference for the right or left paw?

Nancy Galles, Manitou Springs, Colorado

THIS IS AN AREA of much debate in the dog-eat-dog world of animal psychology. But the evidence suggests that some animals favor one side for certain tasks—a phenomenon known as lateralization. For instance, a recent study found that toads who had tape stuck to their backs usually used their right forepaw to get it off. Tool-wielding New Caledonian crows like to monitor with the right eye when manipulating objects in their claws, and humpback whales prefer to surface right side up when capturing prey. Lemurs, meanwhile, are usually lefties when it comes to grabbing their grub. Why do such preferences exist? According to biopsychologist William Hopkins, who studies lateralization in apes at Atlanta's Yerkes National Primate Research Center, "for animals and humans alike, the nervous system is more efficient if the two halves of the brain assume separate functions. If you want to peel a banana, you need one hand to hold the banana and the other to take the peel off. If both sides of the brain have to do both activities, you're not being very efficient." Witness the ambidextrous chimpanzee: In captivity, it typically picks branches up with its left hand but digs peanut butter out of a tube with its right. And when it comes to hurling feces at passersby, chimps that throw overhand tend to do so with the right hand, while underhanders switch from right to left. Go figure.

Q) Why doesn't the hair on your eyelids need trimming?
Scott Myers, New York, New York

"THE ANSWER," says Sarah Millar, a professor of dermatology at the University of Pennsylvania, "is right in front of your eyes: Eyelashes don't have to be trimmed because they don't grow very long." They're programmed, Millar explains, to reach only a certain length—about a quarter of an inch—and then stop. Any longer and they'd be more a hindrance (obscuring your vision) than a benefit (protecting against dust and light). Like all human hair, eyelashes go through a three-part growth cycle. In the first phase, called anagen, they grow from tiny follicles in the skin; next, they stop growing and the follicle goes dormant; finally, the hair clings to the follicle until being shed. All hair grows at the same rate, so length depends on how much time is spent in the growing stage: a few months for eyelashes and body hair, several years for scalp hair. Or perhaps forever, if you're Willie Nelson.

Q) Do eels really migrate to the Sargasso Sea?
David Maahs, Albuquerque, New Mexico

NEARLY ALL of the world's freshwater eels migrate to their ancestral homes in the ocean to spawn, but of the dozens of species out there, only the two North Atlantic ones—the American and the European eel—do it in the Sargasso, a two-million-square-mile ellipse of glassy water that stretches southeast from Bermuda. Their larvae begin life in these famously weed-choked waters and travel hundreds or even thousands of miles to the rivers and lakes of North America and Europe. Eel specialist David Noakes, a professor of zoology at the University of Guelph, in Ontario, Canada, says the Sargasso, which is a warm-water eddy of the Gulf Stream, is ideally located to give the larvae, or leptocephali, a free ride to their freshwater stomping grounds—a trip that takes a year for American eels and up to three years for their Euro cousins. Once there, the slimy, snakelike fish live for 15 or 20 years, growing to lengths of between three and five feet. In the autumn of their lives, the eels return to the Sargasso to spawn—on the way they'll even slither onto wet ground to cross land barriers up to a mile long—and then die. "Being an eel is a tough way to make a living," Noakes says. "Next to the tuna, they're probably the hardest-working fish in the ocean."

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