XI. Progressive Development Through The Different Cycles Of Culture

At the same time this enabled man to develop something which he did not possess before; he became capable of forming red blood. Before that time all human beings had a constitution which gave them the same temperature as their environment; if they were surrounded by a higher temperature, they were adapted to it. Red blood did not exist at that time and the animals above the stage of amphibians are human bodies which have remained behind at a much later stage of development. After the epoch in which man began to develop red blood, the animals also began to develop into warm-blooded beings.