HOW COME? What's in the camel's hump

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Is it true that camels store water in their humps? asks a reader.

A camel's body is ideally suited to the extreme dryness and the extreme temperature swings of desert living: daytime heat, nighttime cold, fiercely blowing sand, and little access to water.

We think of camels as plodding through the deserts of countries like Saudi Arabia. But surprisingly, the (rabbit-sized) ancestors of modern camels evolved in North America, more than 40 millions years ago. By 2 million years ago, herds of the camel's immediate ancestor, Procamelus, had wondered over a land bridge into Asia.

Today, there are only two living species of true camels. Two-humped Bactrians live in Central Asia. One-humped dromedaries roam the Horn of Africa and the Middle East.

All camels have long, thick, curling eyelashes. The fringe neatly catches blowing sand, keeping it out of a camel's big brown eyes. Camels also have a third eyelid, which slides closed from the side. In air full of blowing sand, a camel can shut his (very thin) third lid, and still see well enough to trudge on.

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A camel's jutting brow bones and bushy brows shade his eyes from blinding desert sun. His flaring nostrils can shut tight against wind-borne sand. And his small, furry ears help keep out annoying ear sand.

A camel's temperature automatically adjusts to the air temperature, falling as low as 93 degrees during cold desert nights, then rising to nearly 106 degrees during the searing days. A camel's body can also recycle water from his kidneys, sending it to one of three stomach compartments and then back into the blood. Look at a camel's blood under a microscope, and you'd see that the red blood cells are oval rather than round like those of other mammals. The streamlined shape allows oxygen-carrying cells to ease through vessels, even when a camel is dehydrated.

And then there are those humps. Although a camel's hump isn't actually full of water, it does keep a camel cooler in hot weather. Packed inside the humps are fat, up to 80 pounds in a single mound.

How does all that extra padding help on a 120-degree afternoon? Fat inside the hump absorbs and traps heat, slowing its descent to a camel's vital internal organs. Meanwhile, the rest of a camel's body, especially his spindly legs, radiates heat into the air.

But above all, the hump is a camel's emergency food supply, like a hiker's backpack stuffed with trail mix, turkey jerky and energy bars. A hump (or two) allows a camel to survive for several weeks without actually eating. As the fat is burned for energy, the hump gradually shrinks, becoming flabby and floppy.

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