science of constructing artificial systems that have some of the characteristics of living systems. Bionics is not a specialized science but an interscience discipline; it may be compared with cybernetics. Bionics and cybernetics have been called the two sides of the same coin. Both use models of living systems, bionics in order to find new ideas for useful artificial machines and systems, cybernetics to seek the explanation of living beings' behaviour.

Bionics is thus distinct from bioengineering (or biotechnology), which is the use of living things to perform certain industrial tasks, such as the culture of yeasts on petroleum to furnish food proteins, the use of microorganisms capable of concentrating metals from low-grade ores, and the digesting of wastes by bacteria in biochemical batteries to supply electrical energy.

Mimicry of nature is an old idea. Many inventors have modeled machines after animals throughout the centuries. Copying from nature has distinct advantages. Most living creatures now on the Earth are the product of two billion years of evolution, and the construction of machines to work in an environment resembling that of living creatures can profit from this enormous experience. Although the easiest way may be thought to be direct imitation of nature, this is often difficult if not impossible, among other reasons because of the difference in scale. Bionics researchers have found that it is more advantageous to understand the principles of why things work in nature than to slavishly copy details.

The next step is the generalized search for inspiration from nature. Living beings can be studied from several points of view. Animal muscle is an efficient mechanical motor; solar energy is stored in a chemical form by plants with almost 100 percent efficiency; transmission of information within the nervous system is more complex than the largest telephone exchanges; problem solving by a human brain exceeds by far the capacity of the most powerful supercomputers. These exemplify the two main fields of bionics research—information processing and energy transformation and storage.

The general pattern of the information network of living organisms is the following: environmental sensations are received by the organs of sense and then coded into signals that are transmitted by nerves to the centres of processing and memorization of the brain. Pit vipers of the subfamily Crotalinae (which includes the rattlesnakes), for example, have a heat-sensing mechanism located in a pit between nostrils and eyes. This organ is so sensitive that it can detect a mouse at a few metres' distance. Though much more sensitive man-made infrared detectors exist, bionics can still profit from study of the vipers. First, it would be interesting and of potential value to understand the principle of energy transformation occurring in the rattlesnake's infrared pit, as well as the process by which the nerves are stimulated in the absence of an amplifying mechanism. Another striking example is the odour-sensing organ of the silk moth, Bombyx (silkworm moth) mori. The male can detect the chemical secreted by the female in a quantity as small as a few molecules.

In a conductor such as a telephone wire, the signal is attenuated as it travels along the wire, and amplifiers must be placed at intervals to reinforce it. This is not the case for the animal nerve axon: (axon) the neural impulse issued from sense organs does not weaken in travelling along the axon. This impulse can travel in only one direction. These properties make the nerve axon capable of logic operations. In 1960 a semiconductor device called a neuristor was devised, capable of propagating a signal in one direction without attenuation and able to perform numerical and logical operations. The neuristor computer, inspired by a natural model, imitates the dynamic behaviour of natural neural information networks; each circuit can serve sequentially for different operations in a manner similar to that of the nervous system.

Another question of interest to bionics is how a living system makes use of information. In changing circumstances, humans evaluate alternative courses of action. Every situation somehow resembles a situation experienced before. “Pattern recognition,” an important element in human action, has implications for bionics. One way to design an artificial machine capable of pattern-recognition properties is to use learning processes. Experimental versions of such a machine have been developed; they learn by establishing and modifying connections among a large number of possible alternative routes in a net of pathways. This learning, however, is still rudimentary and far from human.

The first essential difference between existing electronic computers and the human brain lies in the way their memories are organized. In either the memory of a living being or that of a machine, the main problem lies in retrieving information once it has been stored. The method computers (computer) use is called “addressing.” A computer memory can be compared to a large rack of pigeonholes, each having a particular number or address (location). It is possible to find a certain piece of information (information processing) if the address—that is, the number of the pigeonhole—is known. The human memory works in a very different way, using association of data. Information is retrieved according to its content, not according to an external address artificially added. That difference is qualitative as well as quantitative. Man-made memory devices are now constructed using associative principles, and there is a great potential in this field.

The second main difference between electronic computers and the human brain resides in the manner of dealing with the information. A computer processes precise data. Humans accept fuzzy data and carry out operations that are not strictly rigorous. Also, computers perform only very simple elementary operations, producing complex results by performing a vast number of such simple operations at very high speed. In contrast, the human brain performs at low speed but in parallel rather than in sequence, producing several simultaneous results that can be compared (see also artificial intelligence).

In the living world, energy is stored in the form of chemical compounds; its use always is accompanied by chemical reactions. Solar energy is stored by plants (plant) by means of complex chemical processes. The energy of muscular motion is derived from chemical changes. The light produced by such living organisms as mushrooms, glowworms, and certain fishes is of chemical origin. In every case the energy transformation is remarkably efficient compared with thermal engines.

A beginning is being made in understanding how these transformations take place in living material and the nature of the complex role played by living membranes. Perhaps some of the limitations of molecular complexity and fragility could be overcome in man-made artificial-energy machines and better results achieved than in natural membranes.