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A PHYSICIST WRITES . . .
(June 2018)
I am writing this column in bed, where I have also been reading a fascinating book called Cat’s Paws and Catapults. From the cover you would think it was an ordinary book of popular science, but it is rather more than that. Written by an American biology professor, Steven Vogel, it sets out to compare the mechanics and ‘technology’ that have been created on the one hand by nature through evolution, and on the other by us humans in inventing and discovering things. Many of the problems faced are similar in each of these two worlds (how to move around, for example), but the actual solutions are nearly all very different!
Prof Vogel admits that as a biologist he had only a basic knowledge of the maths and physics behind (human) technology, and therefore needed assistance in writing the book. Conversely, reading it has greatly increased my appreciation of biology and in particular ‘biomechanics’. I think anyone might enjoy the book whatever their level of scientific knowledge. (Its title is not only a play on words but refers to two items that store energy elastically, ready for sudden release...)
What are the chief differences between nature’s world and ours? Biological nature is wet and flexible, prefers round to flat surfaces (leaves being the main exception), makes no use of metals, and has just one obvious ‘engine’ – the animal muscle. This can only contract and pull, not (itself) push, and it does so by a surprisingly short amount. Hence bodies possess many distance-amplifying levers (as when we lift something by bending the elbow). Continuous rotary motion is found in only one ‘species’. Most things biological evolved slowly over millions of years.
In contrast, our technology has largely appeared in the last few centuries, and at an ever-increasing rate. It is based on dry and mostly rigid components (though flexible electronics are now coming in). It features flat and angular shapes. We use an enormous variety of metals. Our engines and motors (which relieve us of much muscle-work!) are many and varied, and often highly efficient. We often use force-amplifying (hence distance-reducing) leverage, to move heavy things. As for the wheel and all other rotating assemblies, where would we be without them?
(By the way, while reading Professor Vogel’s book I sometimes needed to remind myself of a couple of points: our human bodies are part of nature’s technology. And looking in the opposite direction, when we fashion natural materials such as wood into, for example, floorboards they become our technical products.)
What are some of the tasks that we and all of nature’s life face, in order to keep our two worlds going? Food and energy have to be found and put to use. We humans consume much energy in producing our food and bringing it to table, and more still in making our lives easier and more ‘civilized’ in other ways. In nature the picture is simpler: animals and insects gain energy from food, and in turn use it to find more (and to avoid predators), while plants get food via their roots and from chlorophyll in their leaves, which absorbs sunlight and makes more food.
Manufacture of stuff is another important task. It’s a curious contrast that while the things we make are always dwarfed by the factories that produce them, in nature the factory is the cell, which is devoted to building and maintaining vastly bigger organisms: our own bodies each contain about a hundred trillion cells.
Let’s consider the subject of maintainance further: we like to hope that all our products, whether simple items or complicated devices, will last a long time without much need of repair. When they do break down, we are as likely to throw them away as to mend them! In nature’s world, however, nearly everything is being continuously rebuilt, in a sort of planned maintenance.
And I don’t mean just the ways in which cells are created for healing scratches, or replaced totally in our blood in a period of about four months. Because over a similar time-scale, every single protein molecule in every one of our cells is renewed (from the instructions in the DNA), a necessity because of their fragility. This I think is the most remarkable fact of all that I learned from Cat’s Paws and Catapults. And it happens throughout nature (at different rates), for nearly all the material within a cell – yet the cells themselves, and their properties, are afterwards unchanged.
It’s occurred to me that this is supposed to be a motoring column – so what does the book say about ways of moving around? A relatively short time ago we humans were entirely reliant on our muscles for getting about, like all the lesser animals. Well, look at us now: thanks to the wheel and everything else, we are in danger of losing our ability to walk any distance at all! But why is it wheels never evolved in nature? Perhaps it was the problem of getting nutrients across sliding surfaces (at the axle). Plus the fact that natural ground is mostly too rough for all but the largest wheels to roll over it. (It’s nice to see amputee dogs given wheels, though...)
Yet there is in nature, as I said, one example of rotary motion, with an axle and a bearing of some sort: the humble bacterium possesses a spiral tail which it can rotate in either direction, to push or pull it along (swimmingly). In terms of power output per unit weight, this ‘bacterial engine’ is fifty times more efficient than mammal muscle! How it works is not yet fully understood, and evolution evidently has never found a way of enlarging it to suit higher organisms.
I’m glad to say that I am finishing off this column in my chair at home – having just spent 11 days in hospital (the RBH). It’s a different world in there, where everyone you can see (other than visitors) is either ill or caring for the ill. And doing so with a manner that makes you feel you are their only patient. The outcome of investigations is that I now face a major operation this month. So Mr Editor, I’ll do my best to meet July’s copy-deadline, but forgive me if I miss it!
Peter Soul
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