Historian and Pulitzer Prize winner Carl Degler analyzes the reasons for Darwinism's fall from favor among American social scientists throughout the early and mid-twentieth century and for its revival in recent years. The work is divided into four parts. In the first part, Degler reviews the impact of Darwin on turn-of-the-century social science and its association with the politics of IQ testing, eugenics, and racism. He denies, however, that social scientists of either Darwinian or anti-Darwinian stripe had any real impact on policies like restrictive immigration laws. In Part II, Degler reconstructs the history of the rise of culture as an explanatory concept and its dissociation from biological roots. Degler explains that much of this movement is attributable to ideological factors and not merely to the results of research. Special emphasis is placed upon the influence of Franz Boas, but the work of Margaret Mead, John Watson, and B. F. Skinner is also examined. Part III examines the resurrection of biological modes of thinking in sociology, psychology, philosophy, and political science in the 1960s and 1970s, largely as a result of the convergence of two factors: (1) dissatisfaction with prevailing social science theory, and (2) new discoveries in the life sciences. Degler finds recent use of biology in the social sciences less deterministic and more egalitarian in orientation than the social Darwinism of an earlier era. In his epilogue, Degler explores recent studies in animal awareness to discern future patterns in biologically based social science, including the potential for greater understanding of the biological roots of human morality.