By Patrick Clinton
When there is no apparent cause, such as poison oak or an insect bite, why does skin itch? And why does it feel good to scratch?
Erika Huddleston, Idyllwild, California
Lots of things make us itch, from histamine-releasing chemical reactions to the pitter-patter of tiny insect feet. When there's no apparent culprit, the cause is usually dry skin. "Dry and cracked skin loses flexibility," explains dermatologist Larry Millikan of the Tulane Medical Center. "When you move, it twitches the little nerve endings." That twitch is the itch. Scratching, of course, doesn't do much for dry skin, but it does send a lot of competing messages via the same nerves, enough to briefly drown out the itching message. The problem is that scratching can do further damage, and the healing process itself can cause more itching. Like your mom always said, if you keep picking at it, it'll never get better.
Is there really such a thing as sea level? Isn't the "level" always changing with the tides and melting icebergs and other stuff?
Robert Stovall, Boise, Idaho
Yes, Robert, nothing in our world, not even sea level, is absolute. "Sea level is a hard value to pin down, because it varies a lot around the world due to tides, seasons, and other factors," says Steve Gill of the National Ocean Service. Most of the time, when you hear people talking about sea level, they're referring to some variation on "mean sea level," an average that's based on hourly measurements of water levels taken at various stations around the world. Scientists agree that sea level is currently rising at a rate of about a millimeter and a half per year, a calculation that factors in a whole raft of geophysical variables. For instance, around Galveston, Texas, sea level appears to be rising faster than the global rate because the land there is subsiding, a result of oil extraction, among other things. In other places, such as the coast of southern Alaska, sea level appears to be falling, because the retreat of heavy glaciers is causing the landmass to rise imperceptibly.
So which sea level standard are the elevation figures found on maps based on? Most of them work off of something called the National Geodetic Vertical Datum, a sort of zero point that was calculated in 1929. You'd think we were due for a new fixed point in our lives, and we are: The NGVD is now being replaced by the more accurate North American Vertical Datum, based on 1988 data. And odds are, when the new elevation figures trickle in, you're going to come down in the world.
Why are lizards always doing push-ups?
Jim Caldwell, Torrance, California
It's a form of communication. Lizards use the "push-up display," as it's called, to announce their presence to the world, to attract mates, and to warn competitors off their turf--or basically to say "Yo!" "Yo, baby!" and "Yo' mama!" The precise message depends on the number of push-ups, the position of the tail and legs, and whether the lizard puffs up his throat. (I say "his" throat because males appear to do push-ups with greater frequency than females.) According to University of Oregon biology professor Emilia Martins, whose dissertation involved 150 hours in the field watching some 1,600 calisthenic incidents performed by sagebrush lizards (seriously!), a push-up that means one thing when no one's around can acquire a different significance when, say, an eligible female is sunning herself on the next rock. It's a shame people never picked up on this form of language. Not only would we be more dynamic conversationalists, but, like Jack Palance, we'd all be in terrific shape.
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