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Third Report on a Test of Mcdougall'S Lamarckian Experiment on the Training of Rats


This experiment, to test McDougall's conclusion that the effects of training are inherited, has now been carried on for thirty-six generations, involving the training of 2827 rats. The present position of the problem raised by McDougall may be summarized as follows:

Neither our own experiment, nor that of Crew, shows any evidence of increasing facility in learning attributable to trained ancestry. McDougall's claim that the progressive decline in the number of errors which he found in successive generations of trained rats is an example of Lamarckian inheritance cannot be maintained in face of the facts (a) that he did not keep a control line, (b) that we have found a progressive decline in our trained line similar to McDougall's, but this was paralleled by the control line; moreover, after about twenty-eight generations, the number of errors progressively increased again in both lines.

McDougall's further argument from the change from a zero-day preference for the bright gangway in earlier generations to a preference for the dim gangway in later generations is invalid; it is shown, from his own figures, to be capable of a different explanation.

The discovery of genetic differences in colour pattern and body size between our trained and control lines, presumably due to mutations, emphasizes the difficulty of interpreting genetic differences in facility of learning, even if they should occur, as due to the Lamarckian factor.

The experiment is being continued.