No. 543] PROBLEMS OF -EVOLUTION 



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Mendel. According to the doctrine of Mendel and his 

 followers each organism is composed of a multitude of 

 unit characters, which do not blend nor lose their identity 

 when mixed with others as a result of sexual reproduc- 

 tion, but which may be expected to come out in the end, 

 practically as they went in at the beginning. This con- 

 clusion has modified in a striking manner the entire con- 

 ception of evolution and heredity. We no longer discuss 

 the origin of species, but rather the origin of characters; 

 we no longer rely upon chance to bring out certain hered- 

 itary characters, but are enabled at will to make many 

 analyses and syntheses of these characters. These dis- 

 coveries probably mark the greatest advance ever made 

 in the study of heredity; they have made it probable that 

 evolution proceeds by the evolution of individual charac- 

 ters; but have they shed any light on the method and 

 manner of this evolution? Permutations of Mendelian 

 characters we may have without number, of new combina- 

 tions of these there may be no end, but, so far as known, 

 no new characters are formed by such temporary com- 

 binations, there is no "creative synthesis," no lasting 

 change. Evolution depends upon the appearance of new 

 characters ; the discoveries of Mendel show us how to fol- 

 low old characters through many combinations and 

 through many generations, but they do not show us how 

 new characters arise. These discoveries have given us 

 an invaluable method of sorting and combining hered- 

 itary qualities, but Mendelian inheritance, as commonly 

 expounded, does not furnish the materials for evolution. 



Many modifications of Mendelian inheritance have been 

 described, many alterations of dominance, or blending of 

 characters, the causes of which are not yet well under- 

 stood. Perhaps in these "unexplored remainders" may 

 be found the causes of new characters. It is not yet cer- 

 tain that the unit characters, or rather their determiners 

 in the germ, are beyond the reach of environmental in- 

 fluence; it is not certain that in their mixture with others 

 they never combine or influence each other in such man- 

 ner as to form new unit characters. Indeed, it is difhVult 



