312 



BIOLOGICAL LECTURES. 



theory of instinct must obviously make pure instinct its first con- 

 cern, and keep the general course of evolution always in view. 



It is not my purpose to engage in a critical examination of 

 theories, but to indicate briefly which of the two rival theories 

 now most in favor accords best with facts and general prin- 

 ciples as I understand them. These two theories are the habit 

 theory of Lamarck and the selection theory of Darwin, Wallace, 

 and Weismann. 



2. Embryology and the Lamarckian Theory. — The habit 

 theory is a part of the more general theory of the transmission 

 of acquired characters. This doctrine has never been recon- 

 ciled with the teachings of embryology, the science which 

 deals directly with the phenomena of heredity, and which is, 

 therefore, the touchstone of every theory of inheritance. It 

 is a fundamental tenet in embryology that all organisms repro- 

 ducing exclusively by germs owe their inherited characters 

 to the germs from which they arose, and that germs carry the 

 primordials of adult structure, not by virtue of any mysterious 

 transference of parental features, but by virtue of the consti- 

 tution they bring with them when they arise by division of 

 preexisting germs. That is, I believe, a fair statement of the 

 embryological doctrine of inheritance, which must be the final 

 test of our theories. 



The selection theory propounded by Darwin and Wallace, and 

 further developed by Weismann, starts from the embryological 

 law of germ continuity (Weismann), or, otherwise expressed, 

 germ lineage, and interprets the phenomena of variation, hered- 

 ity, and development, in harmony with this law and the prin- 

 ciple of selection. This theory is incompatible with the idea 

 that instinct is inherited habit. We could not, for example, 

 say with Professor Wundt^ : 



"We have supposed that father can transmit to son the physio- 

 logical dispositions that he has acquired by practice during his own 

 life, and that in the course of generations these inherited dispositions 

 are strengthened and definitized by summation." 



"The occurrence [p. 405] of connate instincts renders a subsid- 

 iary hypothesis necessary. We must suppose that the physical 



1 Lectures on Human and Animal Psychology, p. 40S. 



