458 FACTORS OP ORGANIC EVOLUTION. 



I advanced this proposition a year ago in my Plant Breeding (pp. 9, 

 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 prevalent notion that organisms must necessarily 

 reproduce themselves exactly as "one of the chief inconsistencies in 

 the prevalent conception of the nature of organisms." " While the 

 doctrine of mutability of species has generally taken the place of immu- 

 tability," he writes, "the proposition that like produces like in organic 

 generation is still generally, and I suppose almost universally, accepted. 

 It therefore becomes necessary to suppose that variation is exceptional, 

 and that some reason for the accumulation of variation is necessary to 

 account for the great divergencies seen in different species. * * * 

 The search has been for some cause of the variation; it is more proba- 

 ble that mutability is the normal law of organic action, and that per- 

 manency is the acquired law." I do not suppose that Professor Wil- 

 liams makes definite variation an inherent or necessary quality of organic 

 matter, but that this matter had no original hereditary power, and that 

 its form and other attributes in succeeding generations have been 

 molded into the environment, and that the burden of proof is thrown 

 upon those who assume that life matter was endowed with the property 

 that like necessarily produces like. At all events, this last is my own 

 conception of the modification of the streams of ascent. 



In other words, I look upon heredity as an acquired character, the 

 same as form, or color, or sensation is, and not as an original endow- 

 ment of matter. The hereditary power did not originate until for some 

 reason it was necessary for a given character to reproduce itself, and 

 the longer any form or character was perpetuated the stronger became 

 the hereditary power. 



It is now pertinent to inquire what determined the particular differ- 

 ences which we know to have persisted. The mere statement that some 

 forms became sessile or attached to the earth, and that others became 

 or remained motile, is an assumption that these differences were direct 

 adaptations to environment. Every little change in environment incited 

 a corresponding change in the plastic organization; and the greater and 

 more various the changes in the physical attributes of the earth with the 

 lapse of time, the greater became the modifications in organisms. I 

 believe, therefore, that the greater part of present differences in organ- 

 isms are the result directly and indirectly of external stimuli, until we 

 come into those higher ranges of being in which sensation and volition 

 have developed, and in which the effects of use and disuse and of 

 psychological states have become increasingly more important as factors 

 of ascent. The whole moot question, then, as to whether variations 

 are definite or multifarious, is aside from the issue. They are as definite 

 as the changes in the environment, which determine and control their 

 existence. More differences arise than can persist, but this does not 



