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Francois Jacob

On Constraints And History

In order to obtain a unified world view through science, the question has repeatedly been raised as to the possibility of making bridges between adjacent disciplines. Because of the hierarchy of objects, the problem is always to explain the more complex in terms and concepts applying to the simpler. This is the old problem of reduction, emergence, whole and parts, and so forth. Is it possible to reduce chemistry to physics, biology to chemistry, and so forth ? Clearly, an understanding of the simple is necessary to understand the more complex, but whether it is sufficient is questionable.

This type of question has resulted in endless arguments. Obviously, the two critical events of evolution — first the appearance of life and later that of thought and language — led to phenomena that previously did not exist on the earth. To describe and interpret these phenomena, new concepts, meaningless at the previous level, are required. What can the notions of sexuality, of predator, or of pain represent in physics or chemistry ? Or the ideas of justice, of increase in value or of democratic power in biology ? At the limit, total reductionism results in absurdity…

The problem can be considered a different way. One can look at the series of objects, moving from the simpler to the more complex. Molecules are made of atoms. Therefore, they obey the laws that determine the behavior of atoms. But, in addition, two statements can be made about molecules. First, they can exhibit new properties, such as isomerization, racemization, and so forth. Second, the subject matter of chemistry, the molecules found in nature or produced in the laboratory, represents only a small fraction of all the possible interactions between atoms. Chemistry constitutes therefore a special case of physics. This is even more so of biology that deals with a complex hierarchy of objects ranging from cells to populations and ecosytems…. At the next level, the number of animal species amount to several millions; however, this is small relative to the number that could exist…. Similarly, the human societies with which ethnology and sociology deal represent only a restricted group of all possible interactions between human beings.

Nature functions by integration. Whatever the level, the objects analyzed by natural sciences are always organizations, or systems. Each system at a given level uses as ingredients some systems of the simpler level, but some only. The hierarchy of complexity of objects is thus accompanied by a series of restrictions and limitations. At each level, new properties may appear which impose new constraints on the system. But these are merely additional constraints. Those that operate at any given level are still valid at the more complex level. Every proposition that is true for physics is also true for chemistry, biology, or sociology. Similarly, every proposition that is valid for biology holds true for sociology. But as a general rule, the statements of greatest importance at one level are of no interest at the more complex ones. The law of perfect gases is no less true for the objects of biology or sociology than for those of physics. It is simply irrelevant in the context of the problems with which biologists, and even more so sociologists, are concerned.

This hierarchy of successive integrations, characterized by restrictions and by the appearance of new properties at each level, has several consequences. The first is the necessity of analyzing complex objects at all levels. If molecular biology, which represents a strong reductionist attitude, yielded such a successful analysis of heredity, it was mainly because, at every step, the analysis was carried out simultaneously at the level of molecules and at the level of the black box, the bacterial cell…. And it seems likely that such a convergence of analysis will play an important role in the study of human beings and their societies.

The second point concerns predictability. Is it possible to make predictions at one level on the basis of what is known at the simpler one ? Only to a very limited extent. The properties of a system can be explained by the properties of its components. They cannot be deduced from them….

The third point concerns the nature of the restrictions and limitations found at every step of increasing complexity. Can one explain why, among all the possible interactions at one level, only certain are observed at the more complex one ?… There is no general answer to such questions, and it seems doubtful that there will ever be a specific answer for any one particular level of complexity. Complex objects are produced by evolutionary processes in which two factors are paramount: the constraints at every level control the systems involved, and the historical circumstances that control the actual interactions between the systems. The combination of constraints and history exists at every level, although in different proportions. Simpler objects are more dependent on constraints than on history. As complexity increases, history plays a greater part.

How do constraints and history interact ? Jacob develops this theme by applying to the question the Levi-Strauss metaphor of bricolage in his vision of evolution. [note 1]

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