390 LOTSY, CURRENT THEORIES OF EVOLUTION. 
Linnean species only revealed diversity within, but, by no means, 
variability of that species. - 
That LiINNAEUS forgot his own distinction between varzetates 
levissimae and varietates is psychologically easily understood. 
We all have a tendency to move away from unpleasant facts, and 
the existence of diversity within his species — supposed to represent 
the immutable created units of nature — was of course utterly 
repugnant to LINNAEUS. 
The consequence of this forgetfulness on the part of so exclusive 
an authority as LINNAEUS then was, has become disastrous, because 
from now on diversity and modification became known under the 
same name: variability. This mistake became tenfold worse when 
LAMARCK claimed that modifications tended to become transmittable, 
provided that the agents which caused them were but allowed a 
sufficient time to act. 
From that moment on, all diversity within the Linnean species 
was practically ascribed to variability, caused in the last instance 
by nurture, or, as is more frequently said, by stimuli from the 
external world. : 
That is the view, not only of LAMARCK, but of DARWIN also, who 
towards the end of his life, on July 19, 1881 (DARWIN died April 19, 
1882) wrote to K. SEMPER: „I still must believe that changed con- 
ditions give the impulse to variability, but that they act zm most 
cases in a very indirect manner. But as I said it is a most per- 
plexing problem.” 
Or, no attentive reader of DARWIN’s works can escape the con- 
clusion that each case of variation which he mentions, is either mere 
diversity within a group which he considered to be a species — a 
term whieh he has never defined — or segregation from heterozy- 
gotes, and none of you here present — I am sure — would accept 
a single instance of variability mentioned by DARWIN, as. conclusive 
evidence of the existence of variation, at the present moment. 
The conception of transmittable variability — though born as a 
mistake by the confusion of diversity and variability — had however 
entered the domain of natural science and, apparently, had come 
to stay. | 
The belief in its existence became even so firmly established, 
that from the appearance of Darwin’s Origin in 1859 until about 



