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Human aggression - introduction
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Evolution of aggression - introduction
Pages 9 - 10
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Brain mechanisms of aggression - introduction
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Dynamics of aggression - introduction Pages 21 - 22 - 23
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Notice the simplicity of the system. It could be constructed in the development of the organism by a relatively small number of genetic instructions. Each pathway could be specified by two sets of instructions, one to tell the output cells where to send their axons, and another for the input cells to receive synapses from those axons. Since there are 21 pathways shown and another 16 or so implied (inputs to sensory analyzers and outputs from motor patterning mechanisms), that would require about 80 sets of genetic information. No doubt there several times at much information in addition required for the internal organization of the various components, more for some and less for others. In sum, however, one can imagine that several hundred sets of genetic information could specify the development of such a system. This fits well with the very limited amount of information in the genetic code, considerably less than a million genes, most of them dealing with non-neural information while even the neural information is primarily required for basic motor organization and control.
The evolutionary transformation of offense from the level of the rat to the level of the stumptail macaque monkey is analyzed in the second paper of this section. The motivating stimuli continue to indicate the familiarity and reproductive status of the opponent, but have shifted, at least partly, from olfactory and vomeronasal sensory systems to visual and auditory systems. The motor patterning mechanisms continue to include the bite attack on the back of the opponent as the principal end component, but it is now supplemented by use of the hands in rough restraint and hitting, yanking and shoving.
The evolution of offense follows the same principles as the evolution of other motivational systems of social behavior. This has been formulated as a general law in the paper comparing the rat and monkey: "the outer parts of motivational systems, their sensory and motor portions, change more rapidly during the course of mammalian evolution than does the inner part, the integrational portion, consisting of the motivational mechanisms. The changes in sensory and motor systems take place as shifts in entire modalities, e.g. mouth to hand or olfaction to vision, that extend across all motivational systems rather than being confined to one or another. Motivational mechanisms do not seem to undergo such gradual transformations "
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