214 THE MENDEL JOURNAL 



with, there can be no evolution without change. A change in 

 structure or function is variation. The direction of evolution 

 will necessarily depend upon the " selection " of certain changes 

 and the "ehniination" of others. The great biological controversy 

 of the present time centres around the question, What is the 

 nature of these changes or variations ? If there are two species, 

 one bigger and the other smaller, one swift of foot and the other 

 less swift, the essential problem before us is. Were the changes 

 by which the smaller and less fleet of foot evolved into the bigger 

 and the swifter species of the nature of a thousand and one im- 

 perceptible stages, or did they partake of the nature of a series of 

 definite and appreciable steps ? Those who hold to the view of 

 " continuous variations " maintain the former thesis, while those 

 who beUeve that " discontinuous variations " supply the material 

 of evolution, hold to the latter view. 



Let us try and form a tangible mental picture of the difference 

 between an evolution proceeding on the basis of continuous 

 variations, and that which proceeds on the basis of discontinuous 

 variations. In the evolution of the larger from the smaller species 

 are we to picture a niimber of the individuals among this species 

 as varying to an inappreciable degree in size in the direction of 

 being larger, and that as the result of the mating of such indivi- 

 duals there arises a race, definitely and permanently larger than 

 the parent species, though so slight in extent as to be barely appre- 

 ciable ? And, accepting Darwin's proposition, that it is conceiv- 

 able a variation once arisen may continue to vary for many 

 generations in the same direction, and, therefore, in the course of 

 time the summation of a series of barely appreciable differences 

 will ultimately result in an appreciable advance in size. Or, are 

 we to believe that the difference in size arose by either a single 

 jump or by a series of small but appreciable steps ? 



Now, at this point we need to be careful to draw another 

 mental picture of the difference between the two processes. So 

 far, we have as it were, pictured the outside of the process ; but 

 it is very necessary to picture also that of its inner mode of 

 working. When we picture the outside of the process, we have 

 in mind the body itself of the individuals. But the inner picture 

 focusses our attention upon their reproductive cells or gametes. 

 Now, when an individual's body varies in size, even to an inappre- 

 ciable extent, upon what does this variation depend ? Upon 

 the answer to this question rests or falls the case for evolution 

 by continuous variations. Is the change a permanent one and 

 maintained in inheritance ? For if it be not preserved in here- 

 ditary transmission, it has no evolutionary value, since evolution 

 is simply progress in form and time. Or is it merely a temporary 

 one — a passing response to environmental conditions, and 



