One reader wants to know HOW LONG CAN HUMANS LIVE WITHOUT SUNLIGHT?. In theory, says George Brainard, a neuroscientist at Philadelphia's Thomas Jefferson University, you could live out your normal life span in a dark bunkerwith some important caveats. Lacking sunlight or artificial light, your circadian rhythms would get out of whack, greatly reducing your capacity for quality sleep and making you no fun to be around. Getting night and day desynchronized is thought to double the risk of cardiovascular disease, which could shorten your life. So could cancer, which might result from a lack of vitamin D, an essential nutrient released when sunlight hits your skin. More to the point, without massive vitamin D supplements or exposure to UV light, your muscles would turn to Jell-...
Q) We all know that Europeans brought deadly germs to the New World. Were the tables ever turned?
Kris Romero, Thousand Oaks, California
A) Probably not, says Stephen Kunitz, professor of social and behavioral medicine at the University of Rochester. Most of humanity's big, bad epidemics developed in the cities of Europe, crowded as they were with people and animals. (Measles likely originated in cattle, influenza in pigs, etc.) Hundreds of generations of contact with those bugs allowed the survivors to develop acquired immunities, a luxury Native Americans didn't have. As a result, explains evolutionary biologist Jared Diamond in his Pulitzer-winning Guns, Germs, and Steel, an estimated 95 percent of the New World's Indians died from disease within 150 years of 1492. Some scientists think that evidence of syphilis in the Americas going back at least 800 yearsalong with a European outbreak of that disease just after Columbus's returnindicates it may have worked the opposite way at least once. But recently discovered syphilitic skeletons in Hull, England, possibly predating Columbus, have cast this theory into doubt.
Q) When a fly wants to land on the ceiling, does it do a half roll or a half loop?
Buddy Brown, Lubbock, Texas
A) Neither. For a long time, people believed that the common housefly, Musca domestica, performed a stunt pilot's half-barrel roll when approaching the ceiling. But in 1958, freeze-frame photography revealed that something else was going on. As Caltech insect physiologist Michael Dickinson explains, first the bug-eyed fella flies right side up at a low angle and in a direct line toward the upper deck. Just prior to impact, it instinctively extends its forelegs over its head and grabs the ceiling, using hooks or sticky pads at the ends of its legs. With the fly's front feet firmly grounded, momentum swings the lower half of its body up, like a trapeze artist. Spider-Man's got nothing on Superfly.
Q) Why do some plants survive winter, and some die?
Leo Roop, Tucson, Arizona
A) The cold truth: Most plant cells rupture when jagged ice crystals form inside them, and if enough damage takes place, plants die. Of course, annual species, like geraniums and impatiens, are supposed to croak every year after dropping their seeds. For perennials, various strategies come into play. According to Chris Andersen, a plant physiologist at the EPA, grasses produce antifreeze-like compounds made of sugar and proteins to lower the freezing point inside their cells. Woody-stemmed flowers like lilacs, shrubs such as rhododendrons, and most fruit trees rely on "extracellular freezing," winterizing themselves as the days get shorter by slowly dehydrating their most vital cells, thus forcing any ice to form outside those cells. And conifers protect trunks and branches the same way, plus they grow sappy needles with low moisture content. Such plants aren't just hardy. They're chill.