How Come? Why does a cheetah have spots?

If there were a Land Animal Olympics, polka-dotted cheetahs would sweep the gold medals in sprinting. The average cheetah can accelerate from standing stock-still to 64 mph in 3 seconds. And for short distances (up to about 1,500 feet), a cheetah can speed up to 75 mph.

The dwindling population of cheetahs - down to about 12,000, from more than 100,000 in 1900 - live mainly in Africa south of the Sahara desert, most in parks on the eastern and southern sides of the continent. Cheetahs once also roamed South Asia, including India. But scientists think that there are only 50 to 200 Asiatic cheetahs left, most in Iran and (perhaps) a few in Pakistan and Afghanistan. In other words, there are far fewer cheetahs in Asia than there are spots on a single cheetah. One out of every 10 cheetahs on Earth lives in a zoo.

Though this swiftest of all land animals has spots, it looks nothing like a leopard. Cheetahs are taller and sleeker, with smaller heads and longer tails. Even their paws are different: Always half-extended, the claws help grip the ground as the streamlined, greyhound-like cheetah chases an antelope at freeway speeds.

(Cheetahs are unique vocally, too. They can't roar, but do growl, hiss, meow, and chirp, like furry birds. Like house cats, they are big on purring.)

The average cheetah has tan fur studded with patches of black, in hundreds of round, one-inch spots. While a cheetah's white chest and stomach are spot-free, its tail is dotted, the dots merging into dark, raccoon-like rings halfway down.

Why all the spots? Most scientists think that fur or skin patterns - such as stripes or blotches - help animals blend into their usual surroundings. Now, a study published in October adds to the spotty story.

Scientists at the University of Bristol in the U.K. used a mathematical model of how patterns develop to study the markings of 35 wild cat species. They found that fur patterns tended to correspond to the cats' habitats, how much time they spent in trees, and whether they hunted at night or in the daytime.

Cats living in dense, wooded areas who hunt mainly in dim or dappled light are mostly likely to have elaborate markings. Cats who live in the open tended to have plain coats. How come? Large, patterned cats have an advantage in a sun-dappled forest, since designs provide camouflage for stalking prey. Smaller cats with patterns would also be better hidden from predators.

But cheetahs, the authors note, seem to be among the exceptions: strongly patterned, but living mainly in open sunlight. Perhaps, they suggest, the ancestors of such animals evolved in a dappled, woodsy habitat. When the animals changed their preferred habitats, their markings didn't prove to be a disadvantage. It's also possible, they note, that cheetahs and other such animals spend time in "microhabitats" where their patterns are actually useful.