For K. Lorenz, `conflict is the father of all things', and aggression is one of the four big conflicting drives in living beings, together with hunger, sex (love) and flight (fear, escape).
Like everything else in life, aggression was molded by natural selection and mutation. It is the fighting instinct which is directed against members of one's own species (`like avoids like'). Its essential function is the preservation of the species as a whole. It provides for a balanced distribution of living beings of the same species over the available environment, selection of the strongest by rival fights and defense of the young. It is always favorable for the species if the strongest take possession of, mark (by song, scent, sound, color) and defend a territory and conquer the desired females.
Aggression is a dangerous, because spontaneous, instinct and can become very harmful. Therefore evolution provided for innate behavior - the interaction of all drives - canalization in personal bonds (recognition, friendship, love), in communication (rites, appeasement gestures), in prohibitions (taboos). One example: when a female chimpanzee entered a new room, she presented her behind to every ... chair.
And what about man? Why do reasonable beings behave so unreasonably? Because we are still subject to all the laws of instinctive behavior. Our pride, arrogance and overestimation prohibit us to learn from animals. We are worse than rats. Explosive population rise stops automatically in rat colonies and after a wholesale slaughter enough individual rats survive to propagate the species. This would not be the case for the human race if the H-bomb is used.
But there is a glimmer of hope: we should consider ourselves as the missing link between animals and the real human beings to come. Education, science and peace should provide for a `human' transition.
This is by any standard a very important and actual book. A picture of all the animals considered would, however, have been helpful.
Like the works of R. Dawkins, this book a must read for all those wanting to understand human behavior.