The 1999 Crafoord Prize lectures. Neo-Lamarckian experimentalism in America: origins and consequences.

The 1890s and the first decades of the twentieth century saw a vigorous debate about the mechanisms of evolutionary change. On one side, August Weismann defended the selectionist hypothesis; on the other, Herbert Spencer defended neo-Lamarckian theory. Supporters of Spencer, notably the American paleontologist and evolutionary theorist Henry Fairfield Osborn, recognized that the questions raised by Weismann and Spencer could only be settled experimentally. They called for the application of experimental methods, and the establishment of a new institution for the purpose of confirming the inheritance of acquired characters. To a great extent, the experimental program championed by Osborn and others was implemented and, although it failed to reveal soft inheritance and was soon eclipsed by Mendelian and chromosomal genetics, it did make significant and lasting contributions to evolutionary biology. Thus the importance of methodological and institutional innovation and theoretical pluralism to the progress of science is illustrated and underscored.