46 THE POPULAR SCIENCE MONTHLY 



THE INHERITANCE OF ACQUIRED CHARACTERS 



By LELAND GRIGGS, Ph.D. 



DARTMOUTH COLLEGE 



THE variability of animal bodies is a very evident fact. The indi- 

 viduals of every species show variety in color, form and size. 

 Three types of variability have been discovered; fluctuating variation 

 obeying the laws of chance, mutation appearing as sudden loss or gain 

 of a color or other feature, and acquired characters gained by an indi- 

 vidual in relation to its surroundings. Among these three types are 

 sought the great factors of evolution. It is a singular fact that no 

 great biologist has attempted to use all three of these factors as the 

 basis of his system, but each author has sought to build his hypothesis 

 upon some one all-important factor. 



Fluctuating variation is undoubtedly the greatest of these factors 

 in the part it has played in the history of evolution. It was made by 

 Darwin the corner-stone of his theory when he claimed that natural 

 and artificial selection could produce almost unlimited effects by the 

 elimination of all but the most favorable among thousands of variants 

 in a species. In the debates over the general theory of evolution there 

 has been no argument more often used than the plausibility of Darwin's 

 theory of the survival of the fittest. The public, in accepting the truth 

 of the theory of descent, has come to look upon this factor of fluctuating 

 variation as a necessary part of evolution. In fact, to many profes- 

 sional biologists Darwinism has become synonymous with the survival 

 of the fittest variations. 



The theory of mutation is the most serious opponent of the Dar- 

 winian theory of selection of variations. Based at first on the evidence 

 gathered by De Vries, it has grown in popularity with the growth of 

 the knowledge of the inheritance of unit characters, and with the dis- 

 covery of pure line inheritance. In the minds of many biologists it has 

 the advantage of showing a method of rapid evolution more or less 

 independent of the guidance of natural selection. The more ardent 

 supporters of the theory have claimed for it the position formerly held 

 by the theory of fluctuating variations, trying to show that all evolu- 

 tion must be in the nature of loss or gain of unit characters. 



That the familiar acquired characters of animals should be inherited 

 was once taken for granted, and, in fact, is still a general belief in the 

 world at large. This theory was held by Lamarck to be a great law of 

 evolution. It was defended by Spencer, and assumed occasionally even 



