27'2 PRESIDENTIAL ADDRESS. 



changed environment for crucial observations with regard 

 to use-inheritance. 



. In experiments to test the question of use-inheritance, the 

 difificulty is to exclude the effects (1) of selection and (2) of 

 individual plasticity. As to the first difficulty I have said 

 enough. With regard to the second, all admit that the 

 individual, especially in the early stages of life, is plastic 

 and to some extent moulded by the environment under the 

 influence of which it develops. To what extent is it plastic ? 

 And if the individual effect is in any degree hereditary, 

 what percentage of the individual effect is handed on to the 

 next generation? Those who maintain that the effects of 

 the environment, or of individual use, must, if they are to 

 become ingrained in the race, be long continued and per- 

 sistent, hold, I presume, that only a small percentage of the 

 individual effect is transmitted. If this be so, if the " heredi- 

 tary effect " is but a small percentage of the " individual 

 effect," it will require great care to insure that the small 

 " hereditary effect " (if such there be) is not lost sight of 

 from its being masked or hidden by the far larger " indi- 

 vidual effect," The subject is full of difficulties, logical and 

 biological, and we must be careful not to slur them over. 



In conclusion, I am anxious that the attitude I assume 

 and advocate in this matter of use-inheritance should not be 

 misunderstood. We hear both on the one side and on the 

 other somewhat dogmatic utterances. We are told on the 

 one hand that natural selection has no need of the assistance 

 of a Lamarckian factor of the effects of which there is no 

 shadow of proof, and the modus operandi of which is an 

 inscrutable mystery. We are told on the other hand that 

 natural selection is tottering to its fall. I advocate an anti- 

 dogmatic attitude. I desire to see the matter fairly and 

 temperately discussed, as Darwin would have discussed it 



