W.S. McCulloch


I would like first to place bionics in a broader framework because there are several fields of interest which surround it on all sides. I therefore pick for my title The Imitation of One Form of Life by AnotherBiomimesis. There is nothing new in biomimesis. It is so important in avoiding enemies and catching prey that it is determined in the genes of many insects: the walking stick, the velvet ant, and so on. It has been of enormous importance; it has given us the images of our gods and the costumes of our witch doctors. It has given us, since the wings of Daedalus, all sorts of transportation. We have mimicked and mimicked. There are a few things of which we can boast, like the wheel and the seeking of power from indirect sourcesfirst from the sun by eating each other, so to speak, and then from steam engines and what notall one way or another from the sun until we got fission and now fusion. But aside from sources of power, and from the wheel, most of what we have done has been an imitation. The imitation used to be primarily for our muscular chores: to pump out a mine, to carry material from one place to another, and so forth. The first major deviation from that, curiously enough, was in the steam engine itself. It was not the replacement of the boy who used to push the slide valve by a stick; the boy still did that. That gave us the regenerative cycle. It was by replacement of the boy at the throttle, the boy who controlled the rate at which the steam was admitted to the slide valve, that the first major deviation from doing mere mechanical work came about. I would like to start from that point with what seems to me the major problem we have to face in bionics, as opposed to cybernetics.

Cybernetics, of course, really started with the first governor, the governor of the steam engine. Cybernetics came into its own when Julian Bigelow pointed out the fact that it was only information concerning the outcome of the previous act that had to return. Cybernetics, properly speaking, deals with that part of biomimesis. Of course we properly include the computer in the head, but there is only an inclusion in that part of the great big multiple closed-loop feedback system of this kind. Cybernetics has gone on from there to become a discipline now taught in universities, though it is just starting. It took from 1865 to the present day for it to become so established. It began, typically, in the solution of particular problems of regulation; the regulation of the steam engine being the first, then the regulation of the repeating stations in the Bell Telephone System. There was a marvelous paper by Black about 1930, but not until 1940 did it receive full synthesis, primarily due to Bigelow.

The full field of bionics opens up clearly within the general field of biomimesis, and it is not identical with cybernetics, nor a part of cybernetics. It is actually a broader field. It is concerned, I would say, primarily with an attempt to understand sufficiently well the tricks that nature actually uses to solve her problems, thus enabling us to turn them into hardware. The first hardware we need is the natural numbers because we must have a logically decent theory to work with. I will come back to that later, for it is one of the main problems, I think I know exactly what Jack Steele meant when he coined the word bionics. It is not a new word; it is a word which was used many years ago for what is now called histology. It meant then what it primarily means now; the attempt to know the living unit. That is the first task. From this living unit we can go on. The difficulty with every field like this is that it tends to require an increasing number of people who know two scientific disciplines. Engineering is, in this sense, a scientific discipline, though it differs from the physical sciences, being much more like biology. One has to have a reasonable knowledge of both engineering and biology in his own head, and there is no use in having in one room what should be in one head. This has been a standard failure. I've seen it happen and happen and happen. As a result, what you generally must have is close team play over the years between a youngster from biology and a youngster from engineering, until each knows both disciplines. This is about the only way it happens.

The solutions are going to come as particular solutions of this, that, or the other particular problem. We have now, for the first time, been able to record from the primary olfactory fibers in the frog. We owe that to Lettvin's development of microelectrodes, and to Pitt's theoretical investigations of olfactory receptors. This means that for the first time we are able to record from fibers about 0.2 µ in diameter. Until the last year or two, only about 1 or 2% of neurons were big enough for us to record them individually. Lettvin, Pitts, and Maturana are now in Naples working on the vision of the octopus. It will be a solution of one particular problem. When we get enough of these particular problems solved we are slowly going to see some of the more general aspects of our subjects unfold.

I think our greatest difficulty is at the level of logic itself; we are beginning to realize how great is our idiocy when we open our mouths concerning relations. This is not a new difficulty. In an argument between de Morgan and Jevons as to the utility of Aristotelian logic, one great logician said to the other that Aristotelian logic is no good because it does not follow from it that if a horse is an animal, then the head of a horse is the head of an animal, to which Bertrand Russell could only say, Fortunate, Aristotle, for if a horse were a hydra, or a clam, the head of a horse would not be the head of an animal. The lack of logic of relations is, think, the greatest problem at the present time in this field. We have looked vainly for either a foundation to back it up, or for governmental sources of funds. Most of our brilliant youngsters in logic have to spend half of their time in a department of philosophy and the other half in a department of mathematics, and usually fall between two stools. So, we are going to try to get together a little corporation and go out and beg money, to see if we can't get a few chronic fellowships set up. I think Albert Sperry probably will head up the group. He is very well aware of this problem.

It has become increasingly clear that our mathematics was made for the engineer, not for the biologist. An engineer or a physicist can make a sphere, a plane (or a pretty good imitation of a plane), a cylinder, or something else that he can handle mathematically, whereas we have to take things in the shape in which God gave them to us. The mathematics is going to be difficult. I worked for seven years trying to get a probabilistic logic for the biological problems that von Neuman had put to us. When I got it, it took three or four youngsters to put it in shape. We then realized it was inadequate. Cowan picked up multiple truth value logic and managed to make it work, so that we can now prove an information theoretic capacity in computation. He presented the beginnings of that work about a year ago to the meeting on Bionics at Wright Field and it is now being prepared for publication. I think those of us who are interested in the organizational aspects of living systems will be doing increasing work on a thermodynamics of open systems. I do not think it really exists yet, except for those that are barely open and those which are barely near equilibrium, and they are linear solutions to a highly nonlinear task.

May I point out that one of the things which haunts the engineer when he thinks about the large complicated systems is that he tends to think they must necessarily be relatively unstable, because his own are. That is to suppose that an elephant will be less stable than a germ. The elephant has an ability to survive a lot longer and in more diverse circumstances. We run into this problem in theories concerning nerve cells. It so happens that in order to get an increased information theoretic capacity, one wants more and more complicated and larger neurons, greater complexity of connections, greater size of the component, and greater structural complexity of the component. This is where it should arise, but the engineer looks at me and says My goodness, do you think it could possibly behave properly if it has a thousand buttons on it? Well, on a Purkinji cell there are about a quarter of a million, and the Purkinji cell works very accurately. Engineers think this because in all of the devices that they are trying to build they have to hold the threshold to such a narrow limit, but that isn't the way the nervous system is built. Excitation and inhibition normally almost balance each other on a cell, so activity on one button more or less at the zero point produces a 100% shift in threshold. We have been wrong again and again in our thinking about order, regularity, and stability of structures. We compare our artifacts with natural objects and think that the large and complicated natural objects are as flimsy as our large and complicated artifacts, but this is not true.

The major advance is going to be, as it was in cybernetics, a way of thinking which properly belongs both to the engineer and the biologist. That way of thinking is going to require new mathematics a crucial extension of thermodynamics, and, above all, a logic of relations. As we begin to grow, I think we will begin to see our problem in a much more unified sense. I would like to try to describe to you the thing that has always interested me most, the central nervous system. I am going to try to do it in words which an engineer or a biologist or the man on the street should be able to understand.

The nervous system only exists in animals which are made up of many cells, and it is made up primarily of cells called neurons. Neurons are identified by their affinity for certain dyestuffs. Anatomically, neurons constitute one system, for there is a path from any neuron to any other neuron within the mass of neurons. Electrically, neurons are identified by the impulses that they transmit. Physiologically, the neurons constitute one system, for the sequence of impulses in any neuron is affected by some other neurons and affects some other neurons. The net of these neurons is such that every neuron is ultimately connected to an effector, whether it is a muscle or a gland, and its behavior can be affected by any neuron that can be affected by any sensory transducer, be it a sensory cell or some other transducer, such as a free nerve ending. Every cell of the nervous system is traversed by at least one such path. Next is the locus of adjunctionthe place of connection of two neurons, where the activity of one affects the other. The neuron transmits its effects primarily in one direction, so that a path composed of many in series transmits only in one direction. But there are numerous circuitsclosed loopswithin the nervous system. Closed loops also exist in the sense that every afferent peripheral neuronthat is, every neuron that picks up its impulses from a sensory outputhas its generation or propagation impulses affected by other neurons. What is more, the muscles and glands which are under the control of the nervous system themselves alter the input of the transducers. Closed loops like these can be either regenerative in their activity, like the first cycle of the steam engine, or they can be inverse negative in their action, like the governor. Those circuits which are regenerative over our muscles and glands are effector circuits. They keep us alive. By these we breathe. Circuits which are regenerative within the central nervous system keep us lively. By these we attend. Circuits which are negative feedbacksinverse feedbacksover our muscles and glands, our reflexes, and similar closed circuits within the central nervous system, determine a state to which that part of the system shall return. They do it here as they do it in the engine. The output decreases the input. By the determination of the state of the system they give to behavior its purposive aspect. The notion of a purpose, which is truly alien to physics, but familiar enough in biology and engineering, is the tendency of a system to return when it is pushed away from that state which is determined by its inverse, or negative, feedbacks. And the system considered as a whole has purposes in this sense. It has its own ends. The engineer and the biologist both have to take this always into consideration. The system has a purpose, an end, built into it.

Now, since that is so, we will look at the receptive end of an organism and try to get this clearly stated. The receptive aspect of an organism is that part whence come the signals concerning the world around the organism. They may be touch, taste, smell, sight, hearing, or what you will. Here you deal with specialized structures, each exquisitely sensitive to changes in some form of energy or in the concentration of certain substances. Under normal conditions, it is these changes which are responsible for the pattern of impulses in afferent peripheral neurons, those which bring in impulses from the outside. Thus, under normal circumstances, when the stimulus is the one appropriate for that sense organ and that sense organ is in the state determined by that central nervous system at that time, impulses are signals. If those same impulses arose for any other reason, they would be noise. Signal and noise, necessarily distinguished by biologists and engineers, are both explained perfectly well physically, but they are not distinguished by the physicists. They differ, functionally, as they serve or fail to serve the ends of that organism. I think that this is the kernel of the way one has to think about the central nervous system. All the rest are special devices, special pleadings. It has taken me about thirty years to be able to say just that little so that it is understandable. I think as long as we can manage to get our problems that clearly stated we will have no trouble understanding each other, whether we are biologists or engineers. I want to make one crucial point about where I think we are going to have a major development coming. It is not an easy point to make. I have tried to make it again and again and I have seen Heinz von Foerster try to get it across too. It was not clear to me before the meeting on biosimulation (biomimesis biosimulation is only a bad word for biomimesis) that it is this: if you looked at a natural process you would observe something that goes on in the face of ever-increasing entropy. The resultant natural object is incredibly tough; the structures which evolve are suited to the world in which they evolve, and they are stuck together with what Donald McKay calls nature's glue. If you watch a bunch of little crystals going into solution and a big crystal forming, that big crystal, a very orderly large structure, is forming as a result of an entropic process. If you cut facets on that crystal and put it on your watch chain, entropy begins to take hold of your handiwork and it goes to pot. When we put order into things, we are taking material and torturing it, forcing an order upon it which is not at all something that came from the inside. It was something put upon it. Anything we do of this kind is slated for destruction. It does not evolve properly on its own. There are exceptions, such as Gordon Pask's evolving and growing threads, but in such cases we are making use of nature's glue.

Let me now set all this off from a third field of interest, which is concerned with artificial organisms that are to evolve and to learn. It is not that these are not problems within bionicsthey are, and certainly within biomimesis. But the group of people whose major interest is in those problems will overlap much more nearly with the major group in cybernetics than with the straight bionical problems. What we are witnessing now is a very large popular swing among engineers and biologists to get their heads together. I would prefer to see little cells of bionics start growing. We have had a similar problem before us on at least four occasions in my short lifetime. When something gets noised abroad there rises up a large number of people and, possibly, sources of funds, and there are always those who want to get on the hay scales. There are always empire builders, there are always fourflushers, and they move in on a group like this just as fast as they can. We have had to break up and disband three whole societies which started that way, and start over again from scratch. I would hate to see such a thing as a large unit being organized now. Let it grow in small groups, and let the small groups have at least two fellows, each of whom knows the other one's business. I think, in a plain word of caution, that we ought not to let bionics get too scopy. By that I mean don't let it try to cover the earth, either in topics or in numbers. It is going to be a hard job to understand any living process. I do not think we fully understand any one yet: not a nerve impulse, nor the contraction of a muscle, nor the multiplication of a virus. It will be some time before we do.


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Wordcloud: Affected, Begin, Biologist, Biomimesis, Bionics, Cell, Central, Circuits, Concerning, Cybernetics, Determined, End, Engineer, Evolve, Field, Form, Going, Group, Happen, Head, Imitation, Impulses, Interest, Large, Living, Logic, Major, Mathematics, Muscles, Natural, Nervous, Neurons, Organism, Particular, Point, Primarily, Problems, Properly, Sense, Solution, Something, Start, State, Steam, Structures, System, Think, Understand, Work, Years

Keywords: Problem, Boy, Deviation, Life, Engines, Steam, Interest, Importance, Valve, Framework

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1 Reprinted from Biological Prototypes and Synthetic Systems, Vol. 1, Plenum Press, New York, 1962.
2 This work was supported in part by the U.S. Army Signal Corps, the Air Force [ASD Contract AF 33(616)-7783], and the office of Naval Research; and in part by the National Institutes of Health [Grant B-1865-(C3)].