HISTORY OF ORGANIC EVOLUTION—COULTER Boe 
with evolution in public thought that this criticism of the universal 
application of his conclusions by certain scientific men was taken to 
mean that the theory of evolution was being abandoned. ‘The real 
situation is that every proposed explanation may prove inadequate, 
and. yet the fact of evolution remains to be explained. 
. All the explanations offered are partial explanations, which simply 
means that no one of them applies to all the facts. We need them 
all and more besides. So far from being abandoned, evolution is 
the basis of all biological work to-day. 
The method of comparison and inference continued until the be- 
ginning of the present century. Then came a new epoch in the 
history of evolution. 
(3) EHaperimentation—This may be called the modern period, 
in contrast with the medieval and ancient periods. It was ushered 
in by the work of DeVries, who introduced the experimental study 
of evolution, and announced his explanation of evolution by means 
of mutation. The problem was to discover whether one species 
actually produces another one. It had been inferred that it does, 
but inference is not demonstration. By means of carefully con- 
trolled pedigree cultures, DeVries discovered a plant in the actual 
performance of producing occasionally a new form among its 
numerous progeny. This form bred true and preserved its dis- 
tinctive characters; in other words, it was a new species or at least 
a different species from its parent. Many such species have now 
been observed originating in this way, both in plants and animals. 
That one species can produce another one is no longer inferred, but 
demonstrated, and demonstrated repeatedly. ‘There is no longer any 
doubt, therefore, that evolution is a fact. It is quite a different 
question whether the proposed explanations are adequate. 
When inferences were the only results, in the medieval period of 
evolution, it was natural to extend inference to the evolution of the 
plant and animal kingdoms, and this involved the origin of man. 
In these days there is no such attempt, for experimental demon- 
stration of the evolution of the whole series of organic forms, cul- 
minating in man, is clearly impossible. Biologists, therefore, are 
no longer concerned with the whole story of evolution, but only in 
discovering experimentally how one species may produce another 
one. The fact of evolution is established, but the whole story of 
evolution must remain an inference. 
PRESENT STATUS OF EVOLUTION 
Only a very general statement can be made of the present status 
of evolution, since a full statement would involve an extensive dis- 
cussion. The experimental study of evolution has led to the de- 
velopment of the field of genetics (heredity), a subject which has 
