Before the eighteenth century the demographic impact of the profession of medicine remained negligible. Relatively few persons could afford to pay a … - William Hardy McNeill

An irresistible cycle seemed to operate, repeating patterns of the ancient world where civil strife and war brought disaster... I surmised that patterned and predictable changes were in turn rooted in the very nature of civilization—the ineluctable breaker of custom and eroder of moral codes, and itself a product and expression of rapid technological and social change.

Inferences and large dosages of imagination actually have allowed the construction of a far more adequate understanding of the cosmic and human past than earlier generations achieved. I believe that this is the central intellectual accomplishment of the twentieth century. Innumerable cosmologists, physicists, mathematicians, anthropologists, sociologists, historians, ecologists, ethologists, and other specialists have played their part; a few swashbuckling intellects led the way, and the outlines of an evolutionary worldview, uniting natural and human history, has begun to emerge. It may be convincing for generations to come—or again may not.

The diffusion of alchemy westward, like the movement of astrology eastward, became significant only in the centuries after 200 A.D. The conservatism of learning was such that, even when commercial intercourse had made intellectual contacts possible, little serious interchange took place until severe social stress had disturbed the even tenor of the times in China, India, and Europe. Technology was a little, but only a little, less conservative.