Among those features of man that are supposed to differentiate him from other animals is his intelligence. For a long time, this was considered to be a special faculty, which only men possessed, whereas the behaviour of other animals could be explained in terms of blind instinct. In spite of the findings of ethology, the dichotomy between intelligence and instinctive behaviour persists in the minds of all save the most enlightened, and is still a weapon in the armoury of those who wish to perpetuate the currently accepted dualism between man and other animals. Let us examine the meaning of these terms.
Whether a behavioural response is said to constitute a “tropism”, “a reflex”, an “instinctive act”, or an intelligent one, it must be mediated by a hierarchical organisation of instructions, and differentiated at each step in accordance with environmental requirements. It is clear that these different types of behaviour differ from each other, but they do so in degree rather than in kind. As behaviour develops, and new levels of complexity are attained, the system becomes capable of reacting more and more adaptively to increasingly improbable situations.
Thus simple forms of life are capable of only the most rudimentary discrimination between the various constituents of their respective environments, and have a correspondingly low capacity for individual survival. A more advanced form of life such as the stickleback, is capable of more discriminatory behaviour. Yet during the mating season, the female will respond sexually to any red object, including the male stickleback, who adopts this colour at such a period, but also including such things as red balls or lollipops. A dog’s powers of discrimination are very much higher than those of a stickleback, yet the animal will only be able to distinguish between legitimate visitors and less legitimate ones, after repeated experiences. Needless to say, man’s discriminatory abilities are the highest of all, and his chances of individual survival are thereby maximised. The corresponding development of cybernismic integrity is confirmed neurologically. At each stage in the evolutionary process, the nervous system becomes progressively more centralised: if the brain grows larger and more of the animal’s actions become dependent on it. Thus, if one extracts the brain of a frog, it is still capable of a number of adaptive responses. It can move its leg, for instance, if pricked with a pin. A cat, however, after its brain has been extracted, is quite immobilised, and does not survive very long, whereas a man dies almost immediately.
Is there any radical jump in the course of this process that can be regarded as a frontier between distinct forms of behaviour? The answer is undoubtedly no. The development of the nervous system appears to be a long and continuous process, and there is no reason to suppose that the human one differs from that of its closest relations in the animal world in any radical manner. All that one can say is that the processes of encephalisation and, in particular, encorticalisation, are more highly developed in the former than in the latter.
At one time, the ratio of brain-size to body-size was considered very important in determining the relative “intelligence” of different forms of life. Undoubtedly, the number of connections between neurons or groups of neurons is theoretically more significant, but, nevertheless, the former criterion provides a good indication of intellectual ability. If we apply it, we find that man does indeed obtain a higher rating than his nearest rivals, the ratio being four times higher in the case of a man than in that of a gorilla. On the other hand, it is roughly twenty times higher in the case of a gorilla than it is in that of a bird. This fact is also indicative of the impossibility of establishing a frontier between man and other forms of life on the basis of intelligence.
If learning ability be regarded as a criterion of intelligence, then this conclusion is further confirmed. As Harlow writes: “The existing scientific data indicate a greater degree of intellectual communality among the primates, and probably a greater communality among all animals, than has been commonly recognised. There is no scientific evidence of a break in learning capabilities between primate and non-primate forms. Emergence from the ocean to the land produced no sudden expansion of learning ability. Indeed, there is no evidence that any sharp break ever appeared in the evolutionary development of the learning process.”
In functional terms, one can consider that man is still in possession of that hierarchical organisation of instructions that we may refer to as his “instincts”, and which once determined the behaviour of our remote proto-hominid ancestors. AM that has happened is that, as the result of the development of the brain, and in particular of the cerebral cortex, these instructions can now be applied with greater precision and can thereby give rise to behaviour that is much more adaptive.
Thus the intelligence is not a new mechanism that replaces in any way those that were previously operative, it is merely the ability of the latter to operate in a more discriminatory manner and hence give rise to behaviour displaying higher homeostasis.
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