84 Evolution and Adaptation 
CONCLUSIONS 
In the light of the preceding discussion concerning the 
evidence in favor of the transmutation theory, we may now 
proceed to sum up our general conclusions, and at the same 
time discuss some further possibilities in regard to the 
descent theory. 
The most widely accepted view in regard to the theory of 
organic evolution is that which looks upon the resemblances 
between the members of a group as due to their common 
descent from one original species that has broken up, as it 
were, into a number of new forms. Strictly applied, this 
means that all the vertebrates have come from one original 
species, all the mollusks from another, the echinoderms from 
a third, etc. Even farther back there may have been a com- 
mon ancestral species for any two of the large groups, as, 
for example, the annelids and the mollusks; and if the re- 
lationship of all the many-celled forms be looked upon as 
probable, then they too have originated from one ancestral 
species. 
Many zoologists appear to hesitate to apply strictly this 
fundamental idea contained in the transmutation theory, be- 
cause, perhaps, they feel that it does not fit in with their gen- 
eral experience of living forms. Yet there can be no doubt 
that it is the primary conception of the transmutation 
theory. This is, however, not the whole question, for we 
must further consider the number of individuals of a species 
that are involved. 
In some species there are smaller groups of individuals 
that are more like one another than like other individuals of 
the same species. Such groups are called varieties, and are 
often associated with certain localities, or with a special 
environment. In the latter case they are called local varie- 
ties. Some of these appear to breed true, not only when 
kept under the same conditions, but even when transferred 
