Cat's Paws and Catapults: Mechanical Worlds of Nature and People. - book reviews

Evolution has produced two technologies: nature's biomechanics and human engineering. Steven Vogel is a biologist, but he rejects the isn't-nature-beautiful-and-wise-and-aren't-humans-arrogant-and-clumsy school of engineer-bashing. He wants, he says, to "ruffle our tendency to view nature as the gold standard for design and a great source of technological breakthroughs" -- but without simply glorifying big-brain progress over nature either.

The two technologies are just different, and for good reasons. They solve problems on different size- and timescales, with different materials. They work with different constraints, media, means of storage and transportation, ways of Learning, and mechanisms for transmitting learning. Like Blake, Vogel labors well the minute particulars -- presenting, elegantly and in detail, the two technologies' similarities and striking differences. Biology and engineering illuminate each other here, with joy and wonder.

"When I was a student, the issue was simply put. "Nature has never invented the wheel," went the textbooks. But science progresses, and we now know that a perfectly fine and true wheel and axle does appear in nature.... In the high magnification of an electron micrograph, a bacterial flagellum looks like a carefully drawn set of very regular waves suspiciously like a rigid structure. It turns out to be a rigid helix much like a corkscrew. Instead of passing one wave of bending after another along its length, it spins around, ten to hundred times each second. The base of the flagellum forms a driveshaft that passes through the cell membrane, connecting it to a rotary engine. And the membrane works like a proper set of bearings. The engine bears a curious similarity in both appearance and operation to our electric motors. It's even reversible. The whole thing -- engine and corkscrew -- either singly or in groups, pushes or pulls a bacterium around much the same way a propeller pushes a ship or pulls an airplane.

"* Nature uses fewer flat and more curved surfaces than we do.

* Corners in our technology are abrupt; nature's are more often rounded.

* We most often design to a criterion of adequate stiffness, while nature seems more concerned with ample strength.

* Partly as a consequence, our artifacts tend to be more brittle while nature's are tougher.

* As another consequence, our things move on sliding contacts between stiff objects while nature's objects bend, twist, or stretch at predetermined places.

* As an additional result, we minimize drag with streamlined bodies of fixed shape, but nature often does so with nonrigid bodies that reconfigure in flows.

* Human technology makes enormous use of metals, while metallic materials (as opposed to materials containing metal atoms) are totally absent in nature.

* As a result, we use ductility of metals to prevent crack propagation; nature does as well, but with foams and composites instead.

* Structures with tensile sheaths outside and pressurized fluid inside are both more common and more diverse in natural designs than in ours.

* For such hydrostatic and aerostatic systems, nature's predominant fluid is water while our structures mostly contain air or some other gas.

* Levers in human technology most often amplify force at the expense of distance, while nature's commonest levers amplify distance at the expense of force.

* Surface ships have long played an important role in human technology, but nature overwhelmingly prefers submarines.

* Our factories dwarf the items they produce; nature's factories make products far larger than themselves.

* We judge our devices best when they need only minimal maintenance, but nature's devices get continuously rebuilt.

* Our technology is as dry as nature's is wet.

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