Human Evolution and the Comparative Psychology of Levels
Charles W. Tolman University of Victoria
In notes written in the 1870s and 1880s, and published posthumously some 60 years later under the title Dialectics of Nature, Frederick Engels wrote: "One day we shall certainly 'reduce' thought experimentally to molecular and chemical motions in the brain; but does that exhaust the essence of thought?" ( Engels, 1972, p. 248). He apparently considered the answer to be so obvious that he did not bother to provide it. That Engels took the answer to be negative is obvious from the context of the question, as indeed from the book as a whole and from every thought that he committed elsewhere to paper.
The dialectical view of the world as expressed in the work of Engels is fundamentally, vigorously, and self-consciously anti-reductionist, as is evident in the following comment on heat: "The discovery that heat is molecular motion was epoch-making. But if I have nothing more to say of heat than that it is a certain displacement of molecules, I should best be silent" ( Engels, 1972, p. 253).
Engels's anti-reductionism was expressed positively by a consistent dialectical theory and methodology of levels, not unlike those later advocated by Dobzhansky ( 1941), Novikoff ( 1945), and Schneirla ( 1949; see also Aronson, Tobach, Rosenblatt, and Lehrman, 1972). An essential aspect of Engels's approach to levels was its materialism, an important implication of which had to do with explanation and the relations between levels. For example, regarding chemistry and organic life Engels wrote ". . . chemistry leads to organic life, and it has gone far enough to assure us that it alone will explain to us the dialectical transition to the organism" ( Engels, 1972, p. 249).