Physical, spatial, dynamic necessity

Almost all the behavioral complexities with which psychologists must deal are basically features of this principle. The primate stock is not, as such, any better stock in survival terms than were earlier existing forms; but the arboreal environment permitted the expansion of a race which had both the physical ability and the wit. The various succeeding forms of anthropoid apes and of primitive man appear to exemplify the barrel analogy well, in the sense that there was always a place for more wit than was already at hand.

There was also a place for huge individual differences. In all the higher forms, mutation can function not only to initiate new species, but to initiate traits which lead to the diversification of types within the species. This diversification, together with the endless chromosome reshufflings already mentioned, means literally that personality, a very complex, highly individualized, highly organized sort of thing, was demanded by nature--demanded in the sense that there was a gap waiting for it, and that when, as a result of mutation and recombination, steps led more and more toward filling the gap, they were "selected" rather than "eliminated."

The organism does not adapt itself to the environment; the environment adapts the organism to itself. The kind of thing that man is, and the kinds of thing that individual men are, are both products of a "necessity"--a physical, spatial, dynamic necessity which demands the filling of the gap in the same sense that a vacuum demands the air which will fill it.

The barrel analogy is also useful in reinforcing the point which we shall have to make constantly regarding discontinuity. Species are discontinuous; they are forms distinct enough so that two species, when crossed, cannot produce fertile offspring. Mutations introduce discontinuous; and species, when once defined, maintain themselves independently for vast periods of time. Even within species, as we have seen, there are some mutations that produce important discontinuities. There are also the discontinuities which result whenever the middle of a distribution is eliminated in the competition with some similar form of life, leaving only the extremes.

But the concept of discontinuity usually relates not to discontinuity in a single trait measured on a linear scale, but to basic differences in structural organization. A bird with a new type of wings produced by mutation can fly only if the wings are related in a specific way to its size, shape, and weight; what survives is a new interrelation of parts. Even a very primitive type of "personality" or "organismic structure" reveals basic gaps between viable types of organization, on both sides of which stand fundamentally different systems of interrelationship. So far as one man's inheritance includes genes which another man's inheritance lacks, and so far as the structural possibilities associated with different genes are necessarily discontinuous, there are true discontinuities between all men.