Organic Evolution, Darwinism and the Genesis of Species. 9 
the efficacy of evolution. This is to confound cause and 
effect. Evolution—the act of evolving—can only operate 
on preexisting material. The forms of animal and vegetable 
life on this globe may have attained their present condition 
through a process of development, or unfolding, from some 
primitive form or forms, but evolution could never have 
produced the primitive forms themselves. 
Properly limited evolution can only be modal in its action: 
that is it can only modify a given form under the influence 
of an adequate cause. The development of the chick from 
the egg, or the oak sapling from an acorn, is a case of true, 
(though individual) evolution. So also is the production 
of varieties among domesticated animals and plants; and 
so also is the production of new kinds, or species, of animals 
by the operation of natural causes, when we can show that 
there is reason to suppose that natural causes are capable 
of producing such new forms. It is in this sense—the 
production of new species by natural causes, prominent 
among which are variation and selection—that the term is 
generally, and correctly, used. 
Having now delimited the term and defined the true 
meaning of the word evolution, let us proceed to examine 
the so-called “factors” in the case Before presenting to 
you a necessarily brief review of the history of evolution 
prior to Darwin—a disquisition necessary to a correct appre¬ 
ciation of the work of this great naturalist whose name is 
indissolubly associated with the doctrine itself—I must make 
another definition. In order to gain a right apprehension of 
the influence of any factor in development we must know ex¬ 
actly the material of which it is a factor. In this case the 
material before us is the category known as species. We 
must define the meaning of the word species before we 
can safely postulate a theory of its origin by descent or by 
any other means It is unfortunate for naturalists that the 
name “species”—the origin of which has been the subject 
of such general controversy should be a word so lacking 
in precision, so various in its meanings. To the metaphy- 
