The behaviour of man and other animals shows so many analogies, in outline as well as in detail, that we must assume that in many cases the same mechanisms, instincts, are active in man and animal (instincts in the sense of patterns of behaviour — or parts of them — which are fixed hereditary). Four main regions of agression are discerned in which instincts play a major role: hunting, territoriality, hierarchy, crowding.
Most ethologists don't consider hunting to be an agressive behaviour, but in the case of man there are many indications that — compared with carnivora — his packet of instincts is composed of a number of conflicting parts: maybe this has been caused by the tact that man might have in his behaviour the vestigen of instincts which are older than 10 million years, vestiges of a rather vegetarian way of living, which in the parliament of instincts must be superseded by later developed predatory instincts (see the ambivalency of primitive hunters towards their prey). Besides these instincts insight probably is an extra factor in the agressive behaviour of man. In nature it will last thousands of years before the fittest species of competitive ones is left over. Human insight, on the contrary, enables man to establish much sooner what animal, what other human being is his competitor and then he promptly reacts by killing or by enslaving.
This insight, however, may also give rise to optimism: if one can kill an opponent for profit at short notice one can imagine that man might as well get convinced of the tact that at the long run it will be necessary — from interested motives — to maintain a world with a variety of vegetation, animals and fellow-men.