Kingdoms, Empires, and Domains

A generation or two before Socrates, thinkers classified the world''s organisms into three categories: plants, animals, and man. However, Aristotle recognized that some organisms, such as sponges and sea-fans, share properties of both plants and animals. These became known as zoophytes. Since then, scientists have explored the idea of a "third kingdom." In Kingdoms, Empires, and Domains, leading m...