It may be said that the generic condensation of experience here indicated implies the formation of general and abstract ideas, and that we cannot in face of the evidence accept Locke’s dictum that abstraction is “an excellency which the faculties of brutes do by no means attain to.” Romanes contended[72] that “all the higher animals have general ideas of ‘good-for-eating’ and ‘not-good-for-eating’ quite apart from any particular objects of which either of these qualities happens to be characteristic,” and he quoted with approval Leroy’s statement,[73] that a fox “will see snares when there are none; his imagination, distorted by fear, will produce deceptive shapes, to which he will attach an abstract notion of danger.” According to such views animals form concepts; and concepts belong to the sphere of rational thought. It is not my intention to enter at length into the refinements of psychological distinction. Many psychologists, however, seek to distinguish between, on the one hand, the predominance by natural emphasis, of certain qualities, such as that of being suitable for food, and, on the other hand, the intentional isolation of these qualities for the purposes of thought and rational explanation. Abstraction they regard as a deliberate process applied with rational intent to the material afforded by experience and reflection. Generalization, too, they regard as deliberate, and carried out with like intent. The result is not merely a composite or generic product, but something more subtle and less dependent on sense. “All trees hitherto seen by me,” said Noiré, “leave in my imagination a mixed image, a kind of ideal presentation of a tree. Quite different is my concept, which is never an image.” The concept “tree” is a deliberate synthesis of abstract qualities intentionally isolated, and recombined in accordance with the general relationships which subsist between them.
If we accept this distinction, if we regard abstraction and generalization as intentional mental processes carried out with the rational intent of discovering the relationships of phenomena with the object of explaining them and recombining their essential features in an ideal scheme of thought, we shall probably admit, with John Locke, that these are excellencies which the faculties of brutes do by no means attain to. But we shall none the less see that the predominance of certain salient features in experience by reiterated emphasis in association with natural needs, and the development of generic in place of merely particular re-presentations will afford the appropriate material for abstraction on the one hand, and generalization on the other. Intelligence supplies the embryonic mental structures from which, under the quickening influence of a rational purpose, abstract and general ideas may be evolved.
The essential features of the evolution of intelligence seem, then, to be, first, the development of controlling nerve-centres, by which the responsive action of reflex automatic or instinctive centres may be checked, augmented, or modified; secondly, the increased differentiation and integration of these control centres with extension of the range and complexity of experience in close touch with practical needs; thirdly, the condensation and concentration of experience by the formation of generic products through the reiterated emphasis begotten of recurrent situations having certain salient features in common, though differing in details; and fourthly, an increased plasticity of behaviour, especially in early life, enabling an animal to deal effectually with an environment far less simple than that to which the more stereotyped instinctive behaviour is fitted by inheritance to respond. And this evolution of intelligent behaviour is working its way up to, though as such it cannot reach, the succeeding phase of mental evolution in which the data, supplied by intelligence, are treated with a new purpose for higher ends in the rational thought which seeks to explain the phenomena, and frame an ideal scheme of their relations and interconnections.
Two further points may be noticed. First, that it is during the early and plastic days or months of life that intelligence is setting its seal on animal behaviour, and stamping it with its distinctive character. Adult life is very much what youth has made it; and old age is stereotyped through habit. In times of progress, the character of the race is determined by plastic possibilities of the young. Among them it is that the incidence of elimination makes itself felt, resulting in the survival of those whose intelligence can mould behaviour in accordance with the new circumstances of a wider life.
Secondly, this selection of the intelligent involves the survival of those in whose higher brain-centres there is room for a greater range and variety of interconnection by means of associating fibres. It involves a selective survival of the larger and more finely organized brains. It is probable, as Professor Ray Lankester has recently indicated, that the ridiculously small-brained mammals and reptiles of the past were creatures of instinct with little capacity for intelligent control. Their lives were simple, and their enemies and competitors no better provided with higher brain-centres than themselves. Stereotyped instinctive behaviour sufficed to enable them to hold their own, and meet the requirements of a life of dull and unprogressive monotony. Strength without cunning made these big-framed animals for a while masters of the situation. But among those existing animals whose skeletons indicate an analogous zoological position, there is none which exhibits a cerebral development so poor. And we may fairly conclude that the fact that these huge creatures have left no lineal descendants may be taken as evidence of the importance and value, in evolution, of that cerebral tissue which is the organic basis of intelligence. The higher brain contains the potentiality of that experience without which the evolution of intelligent behaviour in any race of vertebrate animals is impossible.
V.—The Influence of Intelligence on Instinct
We have seen that the relation of instinct to intelligence is essentially that of congenital to acquired behaviour. We have seen, too, that in the Lamarckian interpretation what is acquired in the course of life may be transmitted through inheritance, and thus the intelligent behaviour of one generation may become instinctive and congenital in the next. But serious biological difficulties stand in the way of the acceptance of this interpretation; there is, moreover, little or no evidence of the assumed transmission to offspring of any acquired modifications of structure or behaviour. We have, therefore, been led to infer that instinctive behaviour has been evolved through the selection of adaptive variations of germinal origin, the influence of intelligence being restricted to the fosterage of co-incident variations, that is to say, of those congenital variations which coincide in direction with the acquired modifications of behaviour due to intelligence. It is clear that on this interpretation the influence of intelligence on instinct is more indirect and less simple than that implied by the Lamarckian hypothesis. Intelligence and instinct are in large degree independent, though there is continual interaction between them. We have now to consider the nature of this interaction, and to this end we must indicate the relation of acquired modifications to the hereditary groundwork of the animal constitution.
The basal fact is, that the bodily tissues are subject to a certain amount of structural change during the course of individual life in accordance with the amount of functional strain put upon them. The labourer’s thickened skin, the enlarged and strengthened muscles of the athlete, the juggler’s acquired suppleness are familiar cases. Less familiar instances are afforded under abnormal conditions. Should one kidney from any cause be slowly destroyed, the other will slowly enlarge to carry on the increased work of elimination of waste products; when the larger shin bone of a dog has been removed after injury, the smaller bone becomes thickened to bear the added strain; new joint surfaces are sometimes formed where bones have been broken and the natural joints injured.
One may say that the normal development of any structure depends upon a due amount of use. But, since in the course of strenuous life any organ is from time to time subject to an abnormal amount of strain, it must be fitted to respond to a super-normal call on its strength and functional activity. Were the heart and the lungs, for example, unable to meet the greatly added drain on their energies, due to unwonted and severe exertion, collapse, perhaps death, would ensue if such exertion were imperatively demanded under special circumstances. And it is clear that many wild animals must be not infrequently placed in such circumstances as will subject their muscular structures and the functional activity of their organs of circulation and respiration to a strain nearly up to their extreme limits of endurance. The carnivorous hunter would often fail to secure his prey if his organization were unequal to a hard and prolonged chase; the hunted prey would not survive to procreate his kind if he fell a victim to the first pursuer through inability to stand the exertion necessary to enable him to make good his escape. It is thus, we may believe, through natural selection that a sufficiently high standard of strength and functional endurance is maintained. The failures in these respects are steadily eliminated. It is difficult to realize the great strain put upon a bird’s organization by the migration flight. Some ten times as many birds leave our shores in the autumn as return to them in the following spring. What proportion of these is weeded out in the act of migration we do not know; but we may be sure that only those fitted to stand a severe test of physical endurance return to rear broods which shall inherit in large degree similar vigour of constitution.
Two factors, then, determine the limits of efficiency in the bodily organs—heredity and use. And these two co-operate in such a way that we may say, either that due use is the essential condition of the effective development of the hereditary powers, or that heredity serves to condition their effective development through use. But though closely related, so that each may be regarded as conditional on the other, they are, if we accept the view that acquired characters are not transmitted as such, so far independent in that use adds nothing to, disuse subtracts nothing from, the hereditary store. It is, indeed, difficult to conceive how, on any view, the absence of the conditioning factor of normal use can be the efficient cause of a positive diminution of the balance at the bank of heredity. And Lamarckian thinkers have not succeeded in placing their conception of the matter in the clear light of a working hypothesis.