AGGRESSION
By BRUNSDON YAPP
IT is a commonplace of physiology that when in doubt one tries it on the dog. In broad outline almost the whole of our know- ledge of the working of the human body is built up from experiments on animals, especially dogs, cats, rats, rabbits and guinea pigs, species which have been chosen not so much for their similarity to man as for economic convenience. It is realised that the details of the results of experiments on one species of mammal cannot be generalised to include all the others, any more than the detailed mechanism of one make of car can be assumed to be the same in other models ; but there is now plenty of evidence that the bodies of all mammals (including man) work in the same general way, just as all motor-cars based on the internal combustion engine are basically similar. Our knowledge of the importance of vitamins in human diet is built up from generalisations from work on the lower mammals, especially rats, but since in some important ways rats differ from man in their requirements of vitamins the details must be filled in from work on man himself. Both man and rat need ascorbic acid (vitamin C), but while the rat can make its own from sugar, man must be supplied with his in fruits and vegetables.
On the whole the educated public, having been convinced by Darwin that man is nearer to the apes than to the angels, accepts the animal nature of his body, and is prepared to learn what little physiology it knows from the laboratory. It is different with psycho- logy. It is true that there have been scientists who have claimed that the patterns of behaviour of man and animals are very similar. Pavlov, for instance, a physiologist rather than a psychologist, said that his dogs could be divided into melancholic and choleric types, with the phlegmatic and sanguine in between, and his main groups have much in common with the extroverted and introverted types of Jung. But the attitude of Broad, who can write six hundred pages on Mind and its place in Nature without apparently seriously mentioning animals at all, is much more common. Nevertheless it is perhaps worth while considering whether a study of the behaviour of animals cannot throw light on some at least of the problems of human behaviour. One might expect that the method would have most success with those attributes of man's nature which in common language are spoken of as bestial. Of these aggression is one.
It was discovered some time ago that in birds which live in flocks there is an order of social precedence based on what is called peck-dominance. The order is originally worked out by individual quarrels, sometimes with actual fighting, and when it has been estab- lished a single peck, or the threat of one, by the dominant member of a pair, is enough to make the submissive member move away from whatever is in dispute. The constancy of the order varies with the species of bird; in pigeons there is a good deal of change from tinge to time, but in fowls the original order is generally maintained -as long as the same flock is kept together, though the physiological state of the individual, such as his level of nutrition, may affect his position in the society. It has been found that high-ranking hens, as well as cocks, produce more offspring than their social inferiors.
A similar type of dominance has been found in colonies of apes in captivity, where nut-snatching is used as the criterion. After a group has been together for a little time ape A snatches nuts from apes B, C, etc., without retaliation or resistance, but no one snatches his nuts; B snatches from C and the others, but not from A, and so on down the alphabet until the last ape of the colony has no one from whom he can snatch. Some interesting work has lately been done on the variation of this order by physiological means.
Many of the processes which go on in the body are regulated by secretions which, circulating in the blood, are called hormones, and much attention has been given to the substances of this nature produced by the sex glands. Their chemistry is difficult and obscure, for it has been found that there are several substances of related structure, some found naturally in the body and others • created in the laboratory, which have similar effects; and there is some doubt as to which ones are actually produced by the glands. For present purposes all that matters is that there is one group found predominantly in the female and another in the male. The effects of these two groups are opposite or complementary, the former looking after and producing feminine physiology and the latter masculine. The observations on aggression to which I have referred were made on a group of castrate male chimpanzees; these are not entirely without sex hormones, which are produced in other parts of the body besides the sex glands, but may be looked on as being in a neutral state. They were first of all ranked in order of dominance in the way already described, and then various individuals were injected with appropriate doses of either male or female sex hormone. It was found that the male hormone raised an individual in the nut-snatching hierarchy, while female hormone lowered him.
There is other general evidence connecting aggression with sexuality in animals. Much attention has lately been given to the problem of territoriality in birds, that is the system by which one bird or a pair takes possession of a strictly delimited area of ground and will allow no trespassers of the same species. Such territory is seldom held except in the nesting season, and, perhaps sur- prisingly, has little to do with feeding or food supply. It is generally the cock who marks out the limits of the holding, and he attacks any other male which attempts to enter it; where two birds are equally matched both physically and psychologically fights to the death often occur. For most of the year stags of the red deer live amicably if not very sociably together, but at the approach of the rut they begin to quarrel, and then leave the party one by one. The sex act itself is for the male of many animals at least a symbolic attack ; the domestic drake will bite the head of his wives until they are bare and bleeding, and in the big cats neck- biting is part of the process.
There is strong probability that aggression in man is similarly connected with sexuality, although because of his more complicated psychic make-up the relationship is probably less straightforward and simple. Such an hypothesis would explain the general feeling that man is more dominant than woman, and the increase in sexual activity which accompaniet a war, when an aggressive spirit is encouraged. Dominance in animals is connected not so much with maleness as a whole but with one part of it, the secretion of the sex hormones, and this, though normally associated with the production of sex cells, is not the same thing and may be relatively independent of it. In the experiments on apes which I have described the sterility of the castrates is not affected by the injections, however much their behaviour may be modified. There is no reason to think that man would be any different. In spite of this it is perhaps significant that as our public manners have become less quarrelsome the birth- rate has declined.
The most interesting question that emerges is whether aggression, can be cured by physiological means. Leaving aside the fact that
it is probably as difficult to inject a whole nation as to indict one, even the effects of administering sex hormones to individuals are at present doubtful and the experiments conflicting. Most of the work has been done on sexual delinquents and those suffering from sexual aberrations. Some cures or improvements have been reported, but in other individuals the effects seem to be small or absent. Perhaps this is because the cases whose alleviation has been attempted have been in extreme pathological states, depending on more than one physiological defect, so that they cannot be attacked by the adminis- tration of one hormone only.
It is not uncommon for the first stages in the application of pure science to be slow and disappointing (there was a long gap, for instance, between the discovery of • penicillin and the development of its medical use) but experiment and exploration continue with good hope of ultimate achievement.
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