432 ANNALS NEW YORK ACADEMY OF SCIENCES 



I think we are justified in saying that if mutation was "knovm" to Darwin 

 it must have been, and still is, a veritable fact; and if evolution is a uni- 

 versal law of nature it can not, in that case, exclude mutation. We, there- 

 fore, who believe in general evolution are compelled to decide for ourselves 

 whether mutation has taken place and is now occurring; and we who are 

 really Darwinians — that is to say, we who believe that Darwin set forth 

 correctly the essential steps in the evolutionary process — are interested in 

 knowing whether he actually recognized the fact of "discontinuous varia- 

 tion " or mutation, and, if so, how he fitted it into, or reconciled it with his 

 system. 



The essential factors in organic evolution, from the Darwinian point of 

 view, are: (1) Variation, (2) inheritance, (3) over-reproduction, (4) com- 

 petition, (5) adaptation and (6) selection and sur\dval. The general expla- 

 nation of these factors is as follows: 



1 . All organisms vary continually and in every part of their structures 

 — that is to say, no two individuals are exactly alike in any particular, 



2. Nevertheless, characters anatomical, physiological and psychological 

 are in general transmitted to descendants; in other words, progeny essentially 

 resemble their parents. 



3. More animals and plants are brought into the world than can possibly 

 find means of subsistence. 



4. There results competition for what subsistence there is, or, as it is 

 otherwise called, a struggle for life. 



5. Since out of all the variations that occur in the constitutions or 

 characters of organisms some must happen to be in directions to give their 

 possessors an advantage, or advantages, in procuring the means of existence, 

 as compared with other individuals of the same class, some of the new-born 

 animals and plants are best adapted to their surroundings or "conditions 

 of life." 



6. These best-adapted forms ("the fittest") will win in the struggle 

 for life and are figuratively said to be selected; the unfit will in the end be 

 exterminated. The result is the origination (evolution) of new classes of 

 organisms out of the old ones and their substitution for the earlier classes 

 or groups. 



Not one of these factors was originally discovered by Darwin, but he 

 first discerned their interrelations and bound them together by a consistent 

 and convincing philosophy. He, for example, was not the earliest observer 

 of progressive change in the organization and external characters of animals 

 and plants, but no one before him had had the insight to perceive that this 

 changeability was the manifestation of a force great enough to burst the 

 artificial limits placed about the groups called species and varieties and to 



