44 GENETICS AND EUGENICS 



Summary. Notwithstanding the fundamental nature of 

 the problem of the inheritance of acquired characters, and all 

 that has been said and done to solve it, it still remains an 

 unsolved problem. So far as the inheritance of mutilations, 

 disease, and induced epilepsy are concerned, the evidence is 

 negative or inconclusive. Acclimatization, the effects of 

 changed food supply, and temperature effects can be ex- 

 plained quite as well on other grounds as on that of the in- 

 heritance of acquired characters. Pressure and light effects 

 are somewhat more easily explained as cumulative from 

 generation to generation, i. e., as inherited acquired charac- 

 ters, than as due merely to germinal variation. The same is 

 true of instincts, which, if interpreted as inherited habits, 

 afford the strongest outstanding evidence for the inheritance 

 of acquired characters. Nevertheless even here an alterna- 

 tive explanation is possible. 



The Lamarckian view has been shown by the critical work 

 of Weismann and his followers to be inapplicable to many 

 groups of cases to which it had previously been applied. This 

 is a real service on the part of Weismann. Nevertheless, in 

 fields where the Lamarckian principle has not yet been dis- 

 proved, viz., as regards the effects of use and disuse, it 

 affords an easier and fuller explanation of progressive evolu- 

 tion and of adaptation in particular than does the selectionist 

 view. Further, Weismann and his followers have been forced 

 practically to concede the existence of Lamarckian evolution, 

 that is evolution the course of which is guided in adaptive 

 directions by the environment. For Weismann admits that 

 the environment may cause parallel modifications of soma 

 and germ-plasm. For practical purposes this is just as effec- 

 tive in guiding evolution as if the soma first developed modifi- 

 cations and then handed them on to the germ-cells. That a 

 mechanism for the transmission of acquired characters from 

 soma to germ-cells has as yet not been demonstrated, does not 

 of course disprove the existence of such a mechanism. Such 

 phenomena as memory, having its basis in the nervous sys- 

 tem, and as the control of development and of behavior 



