THE 



POPULAR SCIENCE 



MONTHLY. 



JUNE, 1906. 



CONCERNING VARIATIONS IN ANIMALS AND PLANTS 



By PRESIDENT DAVID STARR JORDAN, 



STANFORD UNIVERSITY 



WITHIN any given species of animals or plants as occurring in 

 nature, variations of many sorts may appear. No one indi- 

 vidual is the exact image of another, either in structure or in function. 

 In theory, at least, no one cell is exactly like another, no one chromo- 

 some the exact duplicate of a mother or a sister chromosome. More- 

 over, no one group or aggregation of individuals is exactly like another, 

 if separated from it by time or space. In the classification of varia- 

 tions we may naturally divide them into individual variations and 

 collective variations. Collective variations are produced by the ex- 

 tension of certain types of individual variations from generation to 

 generation. These form the basis of new species, as gaps are pro- 

 duced within the series by isolation or by the death of intermediate 

 forms. 



Individual variations are again sharply divided into those which 

 are inborn or blastogenetic, and those which are acquired or ontogenetic, 

 produced by the direct influence of environment or by the reaction of 

 the organism from external conditions. 



The inborn variations arising from differences in the original germ 

 cells, male, female or both, or from results of their combination or 

 amphimixis, may be again subdivided as fluctuations, saltations, mon- 

 strosities and hybridizations. So far as we know it is alone from in- 

 born variations, as perpetuated by heredity, as sifted by natural selec- 

 tion and as protected by bionomic isolation, that collective variations, 

 nascent species and new species originate. 



Fluctuations 



The small differences, numerous but slight, and never wanting, 

 which distinguish one individual from another of the same species 



