The scientific study of violence and human nature centres on investigation of what scientists, perhaps by prejudgement, denote as ‘the seat of aggression’, found in the area of the brain known as the limbic system. This area, located low in the central brain, contains three groups of cells, known as the hypothalamus, the septum and the amygdala. Each, when damaged or electrically stimulated, produces changes in the behaviour of the subject. Damage to part of the hypothalamus of male rats, for example, reduces their aggressive behaviour and abolishes sexual performance, while electrical stimulation increases aggression — though ‘stimulated animals attack only [less] dominant animals, which shows that the direction of aggression is controlled by another part of the brain’.2The reference to less dominant animals is important, because it is an observation of great antiquity that groups of gregarious animals arrange themselves into a pecking order, so called from hierarchy among domestic fowl, asserting or conceding rank in accordance with it. Damage to the amygdala of monkeys may decrease fear of and therefore aggressive behaviour towards ‘novel or unusual objects’ but increase fear of fellow monkeys, thus causing the damaged animal to lose rank in its group.
Neurologists cautiously conclude that the reactions to fear, aversion or threat that resolve themselves as aggression — but also as defence — have their origin in the limbic system. They also emphasise, however, the complex relationship of that system with the ‘higher’ parts of the brain, such as the frontal lobes where incoming sensory information is first and most elaborately processed. The frontal lobes, according to A.J. Herbert, appear to be responsible for the ‘regulation and use of aggressive behaviour’, since it is known that damage to the frontal lobes in man may cause ‘uncontrollable outbursts of explosive aggression … not followed by remorse’.3 What neurologists have established, crudely speaking, is that aggression is a function of the lower brain, amenable to control by the higher brain. But how do the different parts of the brain communicate? Two means are through chemical transmitters and hormones. Scientists have discovered that reducing a chemical called serotonin heightens aggression, and they suspect that there may be a peptide which induces its flow. The peptide, however, has not been found, and variations in the level of serotonin are rare. Hormones, the secretions of the ductless glands, are by contrast easily identifiable and one of them, testosterone, produced in the male testes and closely identified with aggressive behaviour, varies widely in concentration. Its administration to humans — whether male or female — heightens aggression. On the other hand, its administration to female rats that are nursing young reduces their aggressiveness towards males, while their maternal protectiveness is stimulated by another hormone altogether. Generally speaking, high levels of testosterone in males make for heightened masculinity, of which aggressiveness is one feature; low levels, however, do not correlate with an absence of courage or combativeness. Evidence for that, for example, is found in the reputation of eunuch bodyguards and the successes of the famous Byzantine eunuch general, Narses. Finally, scientists emphasise, hormonal effects tend to be moderated by context; calculations of risk, that is to say, will offset, both in animals and man, the operation of what may be called instinct.
Neurology has not, in short, yet succeeded in clarifying how aggression is generated or how controlled within the brain. In genetics, on the other hand, there has been some success in showing how context and ‘selection for aggression’ correlate. Since Darwin first proposed the idea of natural selection in 1858, scholars in many disciplines have sought to establish it on an incontestable scientific basis. Darwin’s original work was based merely on the external observation of species, which led him to suggest that individuals best adapted to their surroundings were the more likely to survive to and in maturity, that the offspring of such survivors, by inheriting their parents’ characteristics, would survive in larger numbers than those of the less well adapted, and that their inherited characteristics would eventually dominate within the species as a whole. What made his theory revolutionary was the argument that the process was mechanistic. Parents, he stated, could pass on only those characteristics they inherited, not — as his contemporary Lamarck contested — those that they acquired. How such characteristics underwent change for yet better adaptation — by the process we call ‘mutation’ — he could not yet explain. Indeed, there is still no explanation of how mutation occurred in the primary organisms from which the myriad varieties of species descend.
Mutation is nevertheless an observable phenomenon; mutation for aggression is one of its forms and aggressiveness is clearly a genetic inheritance that may enhance the chance of survival. If life is a struggle, then those who best resist hostile circumstances are likely to live the longest and produce the largest number of resistant offspring; a recent and enormously popular book, The Selfish Gene, by Richard Dawkins, ascribes this process not merely to the product of genetic inheritance but to the gene itself.4 Genetic experimentation, moreover, demonstrates that some strains of laboratory animals are verifiably more aggressive than others and that aggressiveness breeds true into subsequent generations. Geneticists have also identified rare forms of genetic constitution which correlate with exaggerated aggressiveness, the best known of which is the XYY chromosome pattern in human males: about one male in a thousand inherits two Y chromosomes rather than the normal one, and the XYY group yields a slightly disproportionate number of violent criminals.5
Evidence culled from genetic exceptions and even more so from animals bred in laboratory conditions does not, however, supply answers to questions about the aggressive disposition of any existing creature, including man, in its environment. Successful adaptation through mutation, however mutation occurs, is a response to environment, or context, and while it might prove possible, through the new science of genetic engineering, to make ‘point mutations’ in a genetic inheritance and so breed creatures which lack aggressive responses altogether, it would be necessary for their survival to hold them in conditions from which all threat was entirely absent. No such conditions exist in the natural world, nor could they be created. Even were a wholly unaggressive breed of humans to evolve to live in wholly benevolent circumstances, they would still be obliged to kill the lower organisms that cause disease, the insects and small animals that harbour them and the larger animals which compete for food supplies in the stock of vegetation. It is difficult to see how the necessary system of environmental control could be carried on by creatures which lacked aggressive responses altogether.
What is apparent is that the opponents and the proponents of the thesis that ‘man is naturally aggressive’ both pitch their case too strong. Opponents fly in the face of common sense. Observation demonstrates that animals kill members of other species and also fight among themselves; the males of some species fight to the death. It is necessary to deny all genetic connection between man and the rest of the animal world — a position now held only by strict Creationists — in order to discount the possibility that aggression may be part of man’s genetic inheritance. Proponents also go too far, though for different reasons. One is that they tend to draw the boundaries of aggressiveness too wide. Thus a major group of classifiers, who uncontroversially differentiate between‘instrumental or specific aggression’, defined as ‘concerned with obtaining or retaining particular objects or positions or access to desirable activities’ and ‘hostile or teasing aggression’, which is ‘directed primarily towards annoying or injuring another individual’, also include ‘defensive or reactive aggression’ which is ‘provoked by the actions of others’.6 There is a logical distinction, of course, between aggression and self-defence, which is not invalidated even if the classifiers can show that all three sorts of behaviour they classify together have their origin in the same area of the brain. Such indifferentism also suggests that the proponents of the view that man is naturally aggressive give too little importance to the moderating influence of parts of the brain beyond the limbic system. As has been observed, ‘all animals which show aggressive behaviour carry a number of genes which modify its level of expression’ — so that aggressive impulses are offset by calculation of risk or by matching threat to chance of escape, in the well known ‘fight/flight’ patterns of behaviour — the ability to modify the expression of aggression being particularly marked in humans.7 It seems, therefore, that scientists have so far done little more than identify and categorise emotions and responses which have been eternally familiar. True, we now know that fear and rage have a neural seat in the lower part of the brain, that it is stimulated by the identification of threat in the higher part of the brain, that the two neural areas communicate through chemical and hormonal links and that certain genetic inheritances predispose towards greater or lesser violent response. What science cannot predict is when any individual will display violence. What, finally, science does not explain is why groups of individuals combine to fight others. For some explanation of that phenomenon, in which lie the roots of war, we have to turn elsewhere, to psychology, ethology and anthropology.