ii6 GENETIC VARIATIONS 



the number of generations in which the abnormaUty was 

 inherited was very great.^ 



Thus the action of the environmental conditions on the 

 genie substances is gradual and progressive. The longer the 

 environmental condition acts the greater is the effect pro- 

 duced. And the longer the environmental condition acts, the 

 longer does the acquired character persist; that is, the greater 

 is the number of generations through which it is inherited, 

 after removal from the conditions that induced it. The modi- 

 fied organic substance multiplies itself a millionfold. But 

 finally, as a rule, if the organisms live sufficiently long in an 

 environment that does not contain the effective condition, it 

 loses the acquired character. Thus under new conditions, new 

 inherited characters are acquired, but only after many gener- 

 ations. On restoration to the old conditions, the old character- 

 istics are restored, but again only after many generations. 



In a general view, therefore, we find that the condition and 

 capabilities of the unicellular individual depend on the way 

 its ancestors have lived. If the ancestors have lived for many 

 generations under conditions that gradually injure their genie 

 substances, the injury is handed onto the children, not merely 

 to the third or fourth generation, but to the hundredth or 

 thousandth generation, causing them to be weak and degen- 

 erate. If the parents have lived in such conditions as to acquire 

 new powers, these new powers too are handed on to the hun- 

 dredth generation and later. Their welfare and capabilities 

 depend largely on how their ancestors have lived. The general 

 situation appears to be that which is implied by the terms 

 "Lamarckian inheritance," and "the inheritance of acquired 

 characters." 



Lamarckian inheritance has long been one of the great 

 problems of biology; no subject in this field has been more 

 disputed. One might say that all theory has been for it, all 



