FACTORS OF ORGANIC EVOLUTION. 457 



ruomeut one comes to study tlie genealogies of these subjects or 

 groups, liowever, lie comes upon the astonishing fact that the ancestors 

 are more and more alike the farther back they are traced. In other 

 words, there are great series of convergent histories. Every naturalist, 

 therefore, is compelled to admit that differences in nature have some- 

 how been augmented in the long processes of time. It is unnecessary, 

 therefore, that he seek the causes of present differences until he shall 

 have determined the causes of the smallest or original differences. It 

 is thus seen that there are two great and coordinate problems in the 

 study of evolution — the causes of initial differences and the means by 

 which differences are augmented. These two problems are no doubt 

 very often expressions of the same force or power, for the augmenta- 

 tion of a difference comes about by the origination of new degrees of 

 difference; that is, by new differences. It is very probable that the 

 original genesis of the differences is often due to the operation of the 

 very same physiological processes which gradually enlarge the differ- 

 ence into a gulf of wide separation. 



In api^roaching this question of the origin of unlikenesses the inquirer 

 must first divest himself of the effects of all previous teaching and 

 thinking. We have reason to assume that all beings came from one 

 original life plasma, and we must assume that this plasma had the power 

 of perpetuating its physiological identity. Most persons still further 

 assume that this plasma must have been endowed with the property of 

 reproducing all its characters of form and habit exactly, but such 

 assumption is wholly gratuitous and is born of the age-long habit of 

 thinking that like produces like. We really have no right to assume 

 eitlier that this plasma was or was not constituted with the iiower of 

 exact reproduction of all its attributes, unless the behavior of its 

 ascendants forces us to the one or the other conclusion. Inasmuch as 

 no two individual organisms ever are or ever have 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 un specialized 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 amoeba has no form. The shapes which it assumes are indi- 

 vidual and do not pass to the descendants. To my mind, therefore, it 

 is a more violent assumption to suppose that this first unspecialized 

 plasma should exactly 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 mold in each succeeding generation. I 

 see less reason for dogmatically assuming that like produces like than 

 I do for supposing that unlike produces unlike. 



