The world is full of things that move, walk, lift, fly, and otherwise function. Some of them are alive (such as cats, mosquitoes, trees, fish, and humans), while others were made by human designers (such as cars, buildings, forks, and computers). It is an intriguing question just how similar or different these two "technologies" are in terms of their materials, purpose, and principles of operation. To what degree is a cat's paw like a catapult?
These days, the similarities are embraced with gusto. The fashion in current design circles is the biological metaphor. Computer engineers, mechanical engineers, architects, and many others have "discovered" the concept of mimicking nature in our human-made designs in order to realize elegance, efficiency, and beauty. Although such biological design is not yet mainstream, those who consider themselves the elite of design all talk about it as the obvious next step. From "Natural Capitalism" (which suggests applying biological design to manufacturing operations) to the latest books on AI, we seem to be returning to the idea that "nature knows best."
(This is nothing new, by the way. Aristotle said, "If one way be better than another, that you may be sure is Nature's way." And Leonardo da Vinci said, "Human ingenuity may make various inventions, but it will never devise any inventions more beautiful, nor more simple, nor more to the purpose than Nature does; because in her inventions nothing is wanting and nothing is superfluous.")
The modern manifestation of this attitude arises from the new "network" metaphors that we are exploring with the advent of the Internet-- communities, chaotic (rather than planned) growth, emergent properties, social theories of information. All of these lead naturally to a biological paradigm. And most people talking about it are engineers who are now starting to learn some biology.
In contrast, Steven Vogel is a biologist who knows a lot of engineering because he works in the area of biomechanics-- the study of the mechanical properties of biological creatures. "Cats' Paws and Catapults" explores the contrasts in design principles between biology and technology. As noted in a summary of the book, "Our technology...goes around on wheels...yet in nature only the tiny propellers of bacteria spin as true wheels. Our hinges turn because hard parts slide around each other, whereas nature's hinges (a rabbit's ear, for example) more often swing by bending flexible materials. Why did these 'technologies' take such different paths, and what can we learn from their difference?"
Vogel (whose name means "bird" in German, as I'm sure the German speakers will have noted) is less ga-ga over biological design than the engineers who have so recently discovered the biological design concept. His approach is more balanced and critical-- what can we learn from biology, but at the same time, what can we do better? In his own words, "I began with statements extolling the superiority of nature. In a sense this entire book is my skeptical response. Sure, nature is wonderful. But bear in mind what we do that she doesn't." (p. 310).
This book provides a useful contrast to the current rage over biological design-- a rage which I admit to having embraced in some ways. Vogel writes clearly and with humor, imparting a solid understanding of the basic design principles behind such diverse technologies as squid jets, turbo jets, rabbit ears, snail shells, and steam engines. It rates a strong "+".
The bulk of "Cats' Paws and Catapults" is devoted to exploring various physical qualities (such as size, angles, and stiffness) and actions (such as pulling, pushing, and pumping) as they relate to nature's designs and to our own. There are a couple of fascinating chapters on engines, as well as one on the actual fabrication of all these "widgets" (in factories or through DNA and proteins). You don't need to know any mechanical engineering or biology, but you will come away with a better understanding of both.
In some ways, human and natural design are bound to share commonalities. We are operating in the same physical world, subject to the same laws of physics. You just can't get around things like gravity, the surface tension of water, the local value of the atmospheric pressure, and the principle of self-loading. Hence, there are some clear similarities between biology and our mechanical devices.
For instance, when considering beams that support loads in compression (such as columns on a building or bones in a skeleton), doubling the beam diameter, the beam height, and the load it supports results in a weakening of the system by a factor of two. The beam is four times as strong, but it must support eight times the load, when you consider self-loading. Hence, "if the same design is used, the larger bridge will incur a greater penalty from self-loading; scaled up sufficiently, it will collapse from self-loading alone. Elephants are bonier than cats but still must tread more carefully." (p. 56).
But Vogel's overall conclusions from his thorough examination are clear: "The more closely we look at the technologies of natural selection and of human contrivance, the less similar they appear." (p. 289). In the course of the text, Vogel describes no fewer than 25 fundamental differences between human and nature's technology. These include:
Although Vogel addressed part of the "why?" question during the chapters examining each property, he devotes the remainder of the book to expanding on these ideas and talking about the deliberate imitation of nature.
It turns out that there are fewer than a dozen instances where we have ever truly copied from nature and done better as a result. (Note that Vogel considers only mechanical copying, since this is, after all, biomechanics. Drugs don't count). In many cases, we didn't actually copy, despite romantic claims at the time-- for instance, Brunel's invention of a tunneling shield to be used when digging under rivers, which was supposedly based on the shipworm. Vogel says, "...nature may have played some role, but inflating her contribution demeans splendid engineering achievements." (p. 256). Also, there have been times when we were misled by nature, such as with the design of airplanes. The first ones, which imitated birds or bats, were failures; only by a different design (in which the thrust-producing propeller is separate from the lift-producing wing), wholly unknown in nature, did we achieve flight.
However, there are some successes-- "and impressive ones at that." (p. 257). There is Cayley's brilliant idea to shape ship hulls like streamlined dolphin bodies (although his design had to be modified later when people realized that submarines contend with different fluidic limitations than surface ships). There is the cambering of airplane wings based on similar shapes of bird wings. The telephone transducer mimics the eardrum, and even lowly barbed wire for livestock enclosure is based on a thorny plant called the Osage orange.
Vogel notes that this is hardly a statistically significant number of instances of successful copying. However, he speculates about why copying works only to the limited degree that it does. The most important point is the difference between our two technologies. "Nature's is typically tiny, wet, nonmetallic, nonwheeled, and flexible; human technology is mainly the opposite: large, dry, metallic, wheeled, and stiff." (p. 271). We're just not playing the same game.
But wait, all the modern nature-philes cry! What about all the new possibilities we have for making devices that are wet, or small, or flexible, or some other combination of properties that seems especially biological? Vogel is not a pure cynic: "Where one technology operates in what is normally the domain of the other, emulation holds promise... History isn't destiny... The past history of copying nature may be unportentous, but its scattershot character is no longer representative." (pp. 271, 276, 279).
Vogel sees promise from emulating nature in a number of our new endeavors. Nanotechnology tops the list because it uses nature's principle of making products far larger than the factory that built them. Also included are muscle analogs, smart materials, robotic manipulators, walking vehicles, and swimming by bending. The components of devices may also find inspiration from nature, the best example being composite materials. These are what nature uses instead of metals (structurally; obviously, they lack metals' electrical and thermal conductivity, which has its own evolutionary consequences). Our first successful composite material was fiberglass, but in the future, we should be able to do much better.
The final sections of the book address the complex issue of process in developing both types of technology; the rest of the book was more focused on product. Nature operates through natural selection, but human technology evolves in a cultural setting, including a heady mixture of human creativity, market forces, cultural sanction, economic resources, and political wrangling. Both technologies face barriers to establishment and proliferation, but for rather different reasons. When it comes to process compared to product, Vogel is less convinced of the utility of making analogies between biology and technology. "Natural selection is a most peculiar process, and its limitations are inadequately appreciated. One often encounters analogies between the processes by which human technology changes and natural selection. I think these badly need the scrutiny of a biologist." (p. 298).
Vogel includes a few more examples of questionable connections between the two technologies, including the priviledge of incumbency (in bio-jargon; market jargon calls this "lock-in"), the development of the cone shape, and the issue of steady vs. punctuated evolution. By this point, the reader is thoroughly aware that seemingly clear analogies may hide logical disconnects that invalidate the correspondence. The engineers who are coming to worship biology might do well to brush up on the material.
Overall, "Cats' Paws and Catapults" is a fascinating journey through, just as the subtitle says, the mechanical worlds of nature and people. I came to appreciate just how disparate these worlds are, and why some connections between the two are more meaningful than others. I am all the more fascinated with both cats' paws and catapults, and I have a more balanced view of whether we ought to be modeling one on the other.
Copyright © Kim Allen 2000
