Found: The First Mechanical Gear in a Living Creature Lyrics
With two diminutive legs locked into a leap-ready position, the tiny jumper bends its body taut like an archer drawing a bow. At the top of its legs, a minuscule pair of gears engage—their strange, shark-fin teeth interlocking cleanly like a zipper. And then, faster than you can blink, think, or see with the naked eye, the entire thing is gone. In 2 milliseconds it has bulleted skyward, accelerating at nearly 400 g's—a rate more than 20 times what a human body can withstand. At top speed the jumper breaks 8 mph—quite a feat considering its body is less than one-tenth of an inch long.
The researchers believe that the issus—which lives chiefly on European climbing ivy—evolved its acrobatic prowess because it needs to flee dangerous situations. Although they're not exactly sure if the rapid jump evolved to escape hungry birds, parasitizing wasps, or the careless mouths of large grazing animals, "there's been enormous evolutionary pressure to become faster and faster, and jump further and further away," Burrows says. But gaining this high acceleration has put incredible demands on the reaction time of insect's body parts, and that's where the gears—which "you can imagine being at the top of the thigh bone in a human," Burrows says—come in.
Another odd thing about this discovery is that although there are many jumping insects like the issus—including ones that are even faster and better jumpers—the issus is apparently the only one with natural gears. Most other bugs synchronize the quick jolt of their leaping legs through friction, using bumpy or grippy surfaces to press the top of their legs together, says Duke University biomechanics expert Steve Vogel, who was not involved in this study. Like gears, this ensures the legs move at the same rate, but without requiring a complicated interlocking mechanism. "There are a lot of friction pads around, and they accomplish pretty much of the same thing," he says. "So I wonder what extra capacity these gears confer. They're rather specialized, and there are lots of other jumpers that don't have them, so there must be some kind of advantage."
Even stranger is that the issus doesn't keep these gears throughout its life cycle. As the adolescent insect grows, it molts half a dozen times, upgrading its exoskeleton (gears included) for larger and larger versions. But after its final molt into adulthood—poof, the gears are gone. The adult syncs its legs by friction like all the other planthoppers. "I'm gobsmacked," says Sutton. "We have a hypothesis as to why this is the case, but we can't tell you for sure."
Run on Popular Mechanics, the discovery of natural gears for the first time both shows the variety of the animal kingdom and proposes a model for future gear designs.
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