Gears, though, with their arrays of interlocking teeth – surely not? But here they now are: perfectly formed and rather beautiful cogs, each tooth just 20 thousandths of a millimetre long, intermeshing at the tops of the hindlegs of an insect called a planthopper, which leaps like the grasshopper up to a metre in a single bound. The gears have been discovered by zoologists Malcolm Burrows and Gregory Sutton of Cambridge University, and are reported in the journal Science.
Why do planthopper legs need gearing? They have to move in perfect synchrony as the insect leaps, otherwise it is propelled into a crazy spin. The odd thing is that only the young (nymph) insects do it this way: the mature adults lack the gears, but instead use simple friction to synchronize the legs. It’s not clear why. Perhaps the nymphs, still growing their body parts in successive moulting stages, can easily replace a broken tooth, whereas the adults can’t.
Is this really nature pre-empting the engineer? Biologist Steven Vogel of Duke University in North Carolina, a specialist on the ‘biomimetic’ imitation of nature in engineering, says that’s probably seeing the issue from the wrong angle. In general, he says, we tend to recognize nature’s machines for what they are only when engineers have already given us a human-made analogue – otherwise we probably won’t understand what we’re looking at.
This insistence on seeing nature in terms of our own machines and devices – brain as computer, eye as lens, and so on – has a long history, going back to the “mechanical philosophers” such as Descartes in the seventeenth century. The first microscopists, such as Robert Hooke, usually shared Descartes’ view that all of nature was just mechanics: all forces were effected by atom-sized hooks and pulleys and, yes, cogs. When they failed to find them, they were discouraged and microscopes became merely toys for dilettantes. What a shame, then, that Hooke didn’t include the planthopper among his specimens of flies, fleas and mites. For him and his contemporaries, the microscopic intricacy of the natural world was evidence of God’s craftsmanship. Looking at the extraordinary delicacy of these tiny gears, you can’t help but share his awe at what nature – not God, but natural selection – has wrought.
