It is not possible to acknowledge adequately all our intellectual debts in the brief space available here.  But many who read this volume will recognize our debt to Thomas Malthus, Charles Darwin, Herbert Spencer, Karl Marx, Max Weber, Thorstein Veblen, Albert Keller, William Ogburn, V. Gordon Childe, George Peter Murdock, R.H. Tawney, Sir Julian Huxley, George Garlord Simpson, Leslie White, Julian Steward, Amos Hawley, Marvin Harris, and William H. McNeil, among others. The citations that appear at the end of this volume should be regarded as further acknowledgments of indebtedness and appreciation (1991, p. xviii).