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Biology is capable of evolving functional mechanical gears

Credit: University of Cambridge

It has long been noted in discussions of atomically precise manufacturing that biological molecular machinery provides an existence proof for manufacturing complex molecular machinery. However, proposals for mature atomically precise manufacturing systems resemble scaled down conventional manufacturing systems, with gears and other rigid components familiar at the macroscale. In contrast biological molecular machine systems comprise floppy molecules interacting via controlled Brownian motion. Is it possible for evolution to develop machines with gears, etc.? Apparently evolution is capable of inventing mechanical gears, albeit at much larger than molecular scale. A hat tip to ScienceDaily for reprinting this news release from the University of Cambridge “Functioning ‘mechanical gears’ seen in nature for the first time“:

Previously believed to be only man-made, a natural example of a functioning gear mechanism has been discovered in a common insect – showing that evolution developed interlocking cogs long before we did.

The juvenile Issus – a plant-hopping insect found in gardens across Europe – has hind-leg joints with curved cog-like strips of opposing ‘teeth’ that intermesh, rotating like mechanical gears to synchronise the animal’s legs when it launches into a jump.

The finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists say this is the “first observation of mechanical gearing in a biological structure”.

Through a combination of anatomical analysis and high-speed video capture of normal Issus movements, scientists from the University of Cambridge have been able to reveal these functioning natural gears for the first time. The findings are reported in the latest issue of the journal Science [abstract].

The gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.

The gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement – the legs always move within 30 microseconds of each other … .

This is critical for the powerful jumps that are this insect’s primary mode of transport, as even miniscule discrepancies in synchronisation between the velocities of its legs at the point of propulsion would result in “yaw rotation” – causing the Issus to spin hopelessly out of control.

“This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

“By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force – then if one leg starts to propel the jump the gears will interlock, creating absolute synchronicity.

“In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can’t,” said Burrows. “This emphasises the importance of considering the properties of the skeleton in how movement is produced.”

“We usually think of gears as something that we see in human designed machinery, but we’ve found that that is only because we didn’t look hard enough,” added co-author Gregory Sutton, now at the University of Bristol.

“These gears are not designed; they are evolved – representing high speed and precision machinery evolved for synchronisation in the animal world.”

Interestingly, the mechanistic gears are only found in the insect’s juvenile – or ‘nymph’ – stages, and are lost in the final transition to adulthood. These transitions, called ‘molts’, are when animals cast off rigid skin at key points in their development in order to grow.

It’s not yet known why the Issus loses its hind-leg gears on reaching adulthood. The scientists point out that a problem with any gear system is that if one tooth on the gear breaks, the effectiveness of the whole mechanism is damaged. While gear-teeth breakage in nymphs could be repaired in the next molt, any damage in adulthood remains permanent.

It may also be down to the larger size of adults and consequently their ‘trochantera’ – the insect equivalent of the femur or thigh bones. The bigger adult trochantera might allow them to create enough friction to power the enormous leaps from leaf to leaf without the need for intermeshing gear teeth to drive it, say the scientists.

Each gear strip in the juvenile Issus was around 400 micrometres long and had between 10 to 12 teeth, with both sides of the gear in each leg containing the same number – giving a gearing ratio of 1:1.

Unlike man-made gears, each gear tooth is asymmetrical and curved towards the point where the cogs interlock – as man-made gears need a symmetric shape to work in both rotational directions, whereas the Issus gears are only powering one way to launch the animal forward.

While there are examples of apparently ornamental cogs in the animal kingdom – such as on the shell of the cog wheel turtle or the back of the wheel bug – gears with a functional role either remain elusive or have been rendered defunct by evolution.

The Issus is the first example of a natural cog mechanism with an observable function, say the scientists.

These insect gears are 4 or 5 orders of magnitude too large to be useful in handling molecular fragments for atomically precise manufacturing, so any direct application of this discovery to nanotechnology seems remote. However, it is interesting to note that there are no inherent limitations to the ability of biology to evolve microscale mechanical solutions that resemble components of macroscale manufacturing technology.
—James Lewis, PhD

2 Responses to “Biology is capable of evolving functional mechanical gears”

  1. BioBob Says:

    Sorry, but you have it backwards. Your title really should read “Humans learn to construct functional mechanical gears after 100,000 years of evolution”.

    “There is nothing new under the sun.” Evolution, over billions of years, grinds all possibilities exceptionally fine, and picks the best for that moment through natural selection. Humans have a huge amount to catch-up on; insects are fine teachers of the possible.

  2. tatterdemalian Says:

    Anything humans can build, biology can supposedly evolve. However, it’s not actually capable of evolving that way, any more than a few sextillion molecules can spontaneously assemble to form a nuclear reactor that complies to OSHA standards, and for reasons laid out in the Theory of Natural Selection: the only thing that actually evolves biologically is whatever makes the species more capable of reproducing itself before it dies. This can result in some amazingly sophisticated and specialized behavior, but it also only moves evolution in that one direction, much like liquid water only collects in lakes or flows downhill, never uphill of its own volition.

    The simple truth is that, while evolution could evolve organic gears and wheels and brake systems, unless a lot of very specialized selection pressure is applied and maintained for a very long time, it just won’t evolve on its own. There are simply no transitional forms that don’t cripple any species that starts to evolve them unnecessarily, and so the members of the species that don’t evolve useless appendages that might eventually become true biomechanical gears inevitably wipe out those that do.

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