The author promotes the hypothesis, according to which the variety of political systems is the consequence of differences in the behavior of people belonging to differing human communities. Decisive role in the formation of a political system is assigned to the patterns of people’s behavior in situations when the problem in question is establishment of power. These patterns of behavior differ in the character of resorting to aggression. It is the proportion of frequencies of the said patterns of behavior met within a given human population that determines the type of its political system. Political systems of only one type are compatible with institutions of property rights.