The earliest form of organized society was that into classes founded on the basis of sex,[80] under which the right of individuals to intermarry was restricted to one-fourth of the group. This division of the early race, and the regulations prohibiting conjugal relations with three-fourths the members of the related community, is thought to represent the first coercive abridgment or formal restriction of the then existing conjugal rights, and was inaugurated for the purpose of averting the evil effects arising from intercourse between near relations. Of this early form of society, however, and of the ages during which no organized form existed, little may be known except that which is suggested by the instincts and habits of the highest animals, and that which may be inferred from an investigation of the next higher organization, that into gentes on the basis of kin. Although untold ages intervened between the ancient division of society into classes founded on the basis of sex, and the higher and more important organization into gentes on the basis of kin, this last-named plan for the further development of mankind became universal at a comparatively early stage of human history. [80] Morgan, _Ancient Society_, p. 52. By an investigation of the fundamental principles of the gens, we shall be enabled to observe the similarity existing between the instincts which governed early human action and those which controlled the highest orders of life below mankind. All facts bearing on the primitive conditions of the human race, which in these later times have been brought to light through the investigations directed toward peoples in the various stages of development, only serve to emphasize the importance of the altruistic principle in the formation of organized society and in the establishment of human institutions. Although the gens is the earliest form of organized society of which we have any accurate knowledge, still as within it were encysted the germs of all the principles of justice and equality which our better human nature is beginning again to recognize, and which must characterize a higher stage of progress, a knowledge of its underlying principles is necessary to a correct understanding, not only of the past development of the race and all the existing human institutions, but of the course to be pursued toward the future advancement of mankind. Of the gens, Mr. Morgan says: