CRITIQUE OF DARWINISM 261 
to constitute new species; while De Vries claimed that new species 
were formed by the sudden appearance by mutations of forms specifi- 
cally distinct from the parents. That mutants were new species! 
It seems evident that Darwin did not regard ‘‘saltatory evolution” 
as the common method, while De Vries did. 
Darwin believed that individual, usually small, variations fur- 
nished the material on which selection acts; while De Vries thought 
that mutants, usually large variations, furnished the material. Both, 
however, believed thoroughly that natural selection was a vera causa of 
evolution. 
But things have changed greatly since 1904. The work of 
Morgan, Castle, Jennings and a host of others has shown that many 
mutations are so small, from a phenotypic standpoint, that they are 
quantitatively no greater than the individual variations of Darwin; 
and that they are heritable in the Mendelian way. 
Castle produced a perfectly graded series of hooded rats which 
exhibits almost ideally the steps by which a new form might be 
produced by natural selection. He says: 
“Tf artificial selection can, in the brief span of a man’s lifetime, 
mould a character steadily in a particular direction, why may not 
natural selection in unlimited time also cause progressive evolution in 
directions useful to the organism ?” 
Jennings says: 
“Sufficiently thorough study shows that minute heritable varia- 
tions—so minute as to represent practically continuous gradations— 
occur in many organisms: some reproducing from a single parent, 
others by biparental reproduction. ... . It is not established that 
heritable changes must be sudden large steps; while these may occur, 
minute heritable changes are more frequent. Evolution according to 
the typical Darwinian scheme, through the occurrence of many small 
variations and their guidance by natural selection, is perfectly con- 
sistent with what experimental and paleontological studies show us; 
to me it appears more consistent with the data than does any other 
theory.” 
Many believers in mutation have been needlessly befuddled by 
the diverse meanings of “variations” as used by Darwin and 
De Vries. Darwin included in his “individual variations” both the 
“fluctuating varieties’? and the “mutations” of De Vries. Pheno- 
typically they cannot even now be distinguished. De Vries himself 
candidly admits that this was Darwin’s attitude, thus proving himself 
