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Journal of Experimental Biology 31,307-321 (1954)
Published by Company of Biologists 1954

Fourth (Final) Report on a Test of McDougall'S Lamarckian Experiment on the Training of Rats

W. E. AGAR ¹, F. H. DRUMMOND ¹, O. W. TIEGS ¹, and M. M. GUNSON ¹

¹ The Zoology Department, University of Melbourne

This is the final report of an experiment of 20 years' duration, in which we have repeated, in its essentials, the well-known experiment of William McDougall purporting to reveal a Lamarckian inheritance of the effects of training on rats. The test is one involving light discrimination, and McDougall recorded a steady improvement in the rate of learning on a succession of 32 generations; but he omitted to check the results against a properly conducted control.

Our experiment confirms McDougall to the extent that we too have obtained long duration trends of improvement in learning-rate (Figs. 2, 3); but we find that the effect is not sustained, and that it is, moreover, shown also by a control experiment, using animals of untrained ancestry. This forbids a Lamarckian interpretation.

Statistical analysis of the data indicates that the ‘condition’ of the rat markedly affects its speed of learning, and that progressive changes in learning-rate, over a succession of generations, are in reality correlated with the health of the laboratory colony, which is subject to periods of decline and recovery.