Christian theology was a revised version of Greek philosophy and the effort Plato and his heirs made to discern the permanent behind the sensible, th… - William Hardy McNeill

The rise of Islam offers perhaps the most impressive example in world history of the power of words to alter human behavior in sudden, surprising ways.

Ingenuity, knowledge, and organization alter but cannot cancel humanity's vulnerability to invasion by parasitic forms of life. Infectious disease which antedated the emergence of humankind will last as long as humanity itself, and will surely remain, as it has been hitherto, one of the fundamental parameters and determinants of human history.

Ever since language allowed human cultural evolution to impinge upon age-old processes of biological evolution, humankind has been in a position to upset older balances of nature in quite the same fashion as disease upsets the natural balance within a host's body. Time and again, a temporary approach to stabilization of new relationships occurred as natural limits to the ravages of humankind upon other life forms manifested themselves. Yet, sooner or later, and always within a span of time that remained miniscule in comparison with the standards of biological evolution, humanity discovered new techniques allowing fresh exploitation of hitherto inaccessible forms of life.