302 Heredity. 



believe that the same thing sometimes occurs in nature, 

 and that Darwin has over-estimated the minuteness of 

 the changes in wild organisms, and has thus failed to 

 see that natural selection may give rise to new and well- 

 marked races in a few generations. 



Our theory of heredity would lead us to expect much 

 of this sudden modification, and it gives us a simple ex- 

 planation of its origin, and thus gives to the law of 

 natural selection a much simpler and therefore a much 

 more probable form than that in which it presented it- 

 self to the mind of its discoverer. 



Parallel Variation. 



According to the view that variations are purely for- 

 tuitous, the chances are almost inconceivably great 

 against the independent modification of several forms 

 along parallel lines, by the action of natural selection, 

 yet Darwin gives many instances in which this has act- 

 ually occurred. 



He says that by the term " analogous or parallel vari- 

 ation" he wishes to express that similar characters occa- 

 sionally make their appearance in the several varieties or 

 races descended from the same species, and more rarely 

 in the offspring of widely distinct species. For instance 

 the nectarine is the offspring of the peach; and the va- 

 rieties of both these trees offer a remarkable parallelism 

 in the fruit being white, red or yellow-fleshed, cling- 

 stone or freestone, in the flowers being large or small, in 

 the leaves being serrated or crenated, furnished with 

 globose or reniform glands, or quite destitute of glands. 

 In this case we know that the two forms have indepen- 

 dently varied in parallel lines, and that each variety of 

 the nectarine has not derived its character from a corre- 

 sponding variety of the peach. The several varieties of 



