PLAY AND INSTINCT. 57 



that a variation parallel with this can have been ef- 

 fected in the reproductive substance through which pre- 

 dispositions arose that at once produced a similar 

 tract in the brains of their descendants? This is in- 

 credible. It follows, then, since by supposition only 

 the external environment and not the bodily changes 

 work upon the germ plasm, that any explanation of in- 

 stinct by means of the inheritance of acquired characters 

 is quite impossible. There remains, then, to be consid- 

 ered in this example only the explanation by means 

 of selection, the Darwinian position. This is simple 

 enough, supposing it to be really a case of heredity 

 (as I do not pretend to affirm categorically): it has 

 always been the case that more of those individuals 

 perished who were inclined to walk about carelessly in 

 dark caves and woods. 



Weismann himself has not neglected the question 

 of instinct. He said as long ago as 1883 that all in- 

 stincts have their roots not in the acts of individuals, 

 but rather in germ variation.* In the same lecture he 

 also pointed out that many instinctive acts are per- 

 formed only once in a lifetime — for instance, the flight 

 of the queen bee — and would thus be inherited without 

 practice.f And in a paper on the Allmacht der Natur- 

 zoichtung, 1893, he cites a highly interesting example 

 which seems to exclude every explanation other than 

 that of selection. It concerns, on the one hand, the 

 origin of physical characters and of instincts, and on 

 the other the decadence of the latter. In this case 

 the inheritance of acquired characters is out of the 

 question, as the subject is a sterile individual. The 

 workers among ants are known to be sterile. Among 



* Ueber der Vererbung, Jena, 1883, p. 37. 



f Ibid. See also the remark of Darwin cited above. 



