in the 
nd ear 
Jotaty, 
nts and 
evelop- 
ed, that 
NATURAL SELECTION. 161 
arrived atby a comparison of many biological generalizations, 
we then tried to show was the necessary consequence fol- 
lowing from the Struggle for Existence combined with the 
effects of Inheritance and Variation: the resultant of 
these three forces being what Mr. Darwin calls Natural 
Selection. It must be remembered that Natural Selection 
does not explain the facts of Inheritance and Variation, but 
follows from them and the struggle for Existence. The 
facts of Inheritance and Variation seem to depend upon 
Generation and Nutrition, which are chemical and physical 
phenomena still involved in much obscurity. Before leav- 
ing the subject, it seems proper to mention, as it does not 
appear to be generally understood, that the theory of the 
Evolution of Life may be accepted as true, and yet Natural 
Selection not be considered as a sufficient explanation. 
suppose, now that the attention of naturalists has been 
drawn to the theory of Evolution, that most careful obser- 
vations are made in reference to this subject, and that all 
biologists become convinced in time that plants and animals 
gradually change, the flora and fauna of a remote future 
differing very considerably from those of the present day,— 
the theory of the Evolution of Life might be demonstrated, 
and yet it might be shown that Natural Selection did not 
entirely produce it, or indeed the cause might still remain 
unknown. Let us repeat, then, that whatever may be 
thought of the causes advanced, as sufficient to bring about 
a development of life, the theory of Evolution remains 
the only explanation of the most important generalization 
of the comparative anatomy of plants and animals, their 
Paleontology, Embryology, and Geographical Distribution. 
