"In our earliest history, so far as we can tell, individuals held to an allegiance toward their immediate tribal group, which may have numbered no more than ten or twenty individuals, all of whom were related by consanguinity. As time went on, the need for cooperative behaviour--in the hunting of large animals or large herds, in agriculture, and in the development of cities--forced human beings into larger and larger groups. The group that was identified with, the tribal unit, enlarged at each stage of evolution. Today, a particular instant in the 4.5-billion-year history of Earth and in the several-million-year history of mankind, most human beings owe their primary allegiance to the nation-state (although some of the most dangerous political problems still arise from tribal conflicts involving smaller population units). Many visionary leaders have imagined a time when the allegiance of an individual human being is not to his particular nation-state, religion, race, or economic group, but to mankind as a whole; when the benefit to a human being of another sex, race, religion, or political persuasion ten thousand miles away is as precious to us as to our neighbour or our brother. The trend is in this direction, but it is agonizingly slow. There is a serious question whether such a global self-identification of mankind can be achieved before we destroy ourselves with the technological forces our intelligence has unleashed."