444 Life and Immortality. 



of high classificatory value, and only embryological charac- 

 ters are frequently the most valuable of all. The real affini- 

 ties of all organisms, in contradistinction to their adaptive 

 likenesses, are due to inheritance or community of descent. 

 Hence, a natural system of classification is a genealogical 

 arrangement, with the acquired grades of difference, denoted 

 by varieties, species, genera, families, etc., and their lines of 

 descent have to be discovered by the most permanent charac- 

 ters, whatever they may be and how little of vital importance 

 they may possess. 



That species are immutable productions, which was 

 until quite recently the current belief by laymen and nat- 

 uralists, was almost unavoidable so long as the world was 

 considered to be of short duration. But now that some idea 

 has been acquired of the time that has elapsed since the 

 beginning of earth-life, we are too apt to assume, without 

 proof, that the geologic record is so complete, that it would 

 have afforded us some plain evidence of the mutation of 

 species, if they had undergone mutation. But the principal 

 cause of our unwillingness to admit that one species has 

 given birth to other and distinct species, is that we are 

 always slow in admitting any great change of which we do 

 not discern the intermediate steps. Just such a difficulty 

 was felt by many geologists when Lyell first insisted that 

 long lines of inland cliffs had been produced, and great val- 

 leys excavated, by the agencies which are still at work in the 

 earth. No effort of mind can adequately grasp the meaning 

 of even ten million of years, nor add up and perceive the full 

 effects of the many slight variations to which species have 

 been subjected during an almost infinite number of genera- 

 tions. The day, however, is not distant, when mankind will 

 have become just as thoroughly convinced that species have 

 been modified during a long course of descent, mainly through 

 the Natural Selection of innumerous successive, slight and 

 favorable variations as they are that the attraction of gravi- 

 tation is an important element in the maintenance of the 



