I.] UNLIKE PRODUCES UNLIKE. 21 



been exactly alike, so far as we can determine, it seems to 

 me to be the logical necessity to assume that like never did 

 and never can produce like. The closer we are able to 

 approach to plasmodial and unspecialized forms of life in 

 our studies of organisms, the more are we impressed 

 with the weakness of the hereditary power. Every tyro 

 in the study of protoplasm knows that the araceba has 

 no form. The shapes which it assumes are individual, 

 and do not pass to the descendants. To my mind, there- 

 fore, it is a more violent assumption to suppose that this 

 first unspecialized plasma should exa(;tly reproduce all its 

 minor features than to suppose that it had no distinct 

 hereditary power, and therefore, by the very nature of 

 its constitution, could not exactly reproduce itself. The 

 burden of proof has been thrown upon those who attempt 

 to explain the initial origin of differences, but it should 

 really be thrown upon those who assume that life -matter 

 was originally so constructed as to rigidly recast itself 

 into one mould in each succeeding generation. I see 

 less reason for dogmatically assuming that like produces 

 like than I do for supposing that unlike produces unlike. 

 I advanced this proposition a year ago in my " Plant - 

 Breeding"* (pages 9 and 10), and I am now glad to 

 find, since writing the above paragraph, that H. S. 

 Williams has reached similar conclusions in his new 

 "Geological Biology." He regards mutability as the 

 fundamental law of organisms, and speaks of the prev- 

 alent notion that organisms must necessarily reproduce 



*A3 an example of the common and unreserved acceptance of the notion that 

 like produces like, 1 may cite the opinion of A. S., in a review of Plant-Breeding 

 in the Bulletin of the Torrey Botanical Club (April, 1896). He dogmatically asserts 

 that the statement that inherent plasticity of organisms may allow of variation 

 without an immediate inciting cause, is " certainly unscientific." It is only fair 

 to ask that he explain why it is. 



