262 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 
more clear-sighted than many of his followers. All that Darwin 
needed for his purpose was proof of variations that are heritable, and 
these are found in mutations, be they large or small. 
Just as Mendelism has to do with the mechanism and not the fact 
of heredity, so the mutation theory deals with the nature and not the 
fact of variations. Neither, in my opinion, has any implication that 
is antagonistic to the theory of natural selection. 
The statement has been made that natural selection “ originates 
nothing” because it does not explain the origin of variations. I 
must confess scant patience with this point of view. As well say 
that the sculptor does not make the statue because he does not 
manufacture the marble or his chisel; or that the worker in mosaic 
originates nothing because he does not make the bits of stone which 
he assembles in his design! 
The material corresponding to the bits of stone in the mosaic is 
furnished by heredity and variation, and its quantity by geometrical 
ratio of increase. Natural selection acts in selecting and putting 
together this material in the formation of new species. Thus, in a 
true sense, it seems evident that something new has appeared— 
something that is, but was not. 
Another favorite figure, introduced I believe by De Vries, . is 
“Natural selection acts only as a sieve” determining which forms 
shall be retained and which shall be discarded. This also seems to 
me to fall short of a complete statement of the truth. If the material 
subjected to the sifting process be regarded as changing with each 
generation by the addition of variations, or mutations if you prefer, 
some of which are favorable to a nicer adjustment of the species to its 
environment, the figure would be more nearly correct. To make it 
complete, however, the mesh of the sieve must change from generation 
to generation so that a quantitative variation which would be preserved 
in one generation would be discarded in a later one. But in this case 
natural selection would do more than a sieve could do. It would 
combine a number of favorable variations in the production of 
something new, a new species! 
In conclusion it seems to me that we are justified in maintaining 
that Mendelism and the mutation theory, while forming the basis of 
the most brilliant and important advances in biological knowledge of 
the last half-century, have neither weakened nor supplanted the 
Darwinian conception of the “Origin of species by means of Natural 
Selection.” 
