PRESIDENTIAL ADDRESS. 49 



even reasonable ? If not due to such changes to what causes 

 are they due ? Without pretending to explain how such a thing 

 could happen, I claim that the indications are that it does hap- 

 pen. To say without proof that it cannot happen adds nothing 

 to the argument. We have an antecedent and we have a con- 

 sequent. Both are facts. There is no possibility in the present 

 state of our knowledge of either proving or disproving the casual 

 connection between these facts. Variation takes place in the 

 direction of adaption to changed conditions and activities. So 

 far the inference is confirmed by a third fact. If the inference 

 had not been challenged in the interest of another principle 

 this would be regarded as proof. I do not agree with.Weis- 

 mann that the burden of proof rests on those who draw this 

 natural inference. It rests on him and the Neo-Darwinians to 

 show that the assumed cause is not a cause. This they have 

 thus far failed to do. 



You will understand that I am speaking of variations which 

 take place in the germ-cells and sperm-cells of parental organ- 

 isms before they blend in the fertilized ovum. Most of Weis- 

 mann's argument is directed to show that the fertilized ovum 

 itself cannot be affected by any transforming influence acting 

 upon the mother during the growth of the embryo. This may 

 be true but it is unimportant. The time required to^ develop 

 the embryo is too short for the environment to produce any 

 material change however strongly the tendenc}^ might be at 

 the time in the direction of such change. It is chiefly the un- 

 combined sexual elements which are admitted by all to be un- 

 dergoing specific transformation. The Neo-Darwinians deny 

 that this is due to admittedly parallel transformations going on 

 in the individual, the result of external and internal influences 

 upon the developed body ; the Neo-I^amarckians consider the 

 latter as in great part the cause of the former, while admitting 



