Contenidos: A methodological note on the principle of cumulation / Gunnar Myrdal -- The determinants of collective behavior / Neil J. Smelser -- Marxism / Karl Marx -- The essence of historical materialism -- A general critique of Equilibrium Theory / Mohammed Guessous -- Time and physical process / Richard Schlegel -- Diseases of science / Derek J de Solla Price -- Reasons for sociocultural change and variably recurrent processes / Pitirim A. Sorokin -- Toward a conception of the life cycle of groups / Theodore M. Mills -- Evolution, revolution, reaction / Wilbert E. Moore -- The age of the democratic revolution / R.R. Palmer -- The American Negro problem in the context of social change / Arnold M. Rose -- The United States population explosion: consequences and implications / Philip M. Hauser -- The triple revolution / Ad Hoc Committee on the Triple Revolution -- The nation transformed / Sigmund Diamond -- The nation-state as a unit in the comparative study of social change / Wendall Bell and Ivar Oxaal -- The rate and costs of political development / Manfred Halpern -- Social patterns (structures) and problems of modernization / Marion J. Levy, Jr -- On the origin and evolution of human culture / Harold F. Blum -- Pitfalls and guideposts in comparing organic and social evolution / G. Ledyard Stebbins -- The irreducibility of social change: a comment on Professor Stebbins' paper / Robert A. Nisbet -- Some misgivings about Evolutionary Theory: a comment on Professor Stebbins' paper / Wilbert E. Moore