CHAPTER IX. 



THE MUTATION THEORY AND MUTATIONS. 



INTRODUCTORY. 1 



Much has been said and written on the subject of the origin of species, and yet 

 the solution of the problem is far from complete. The latest advances in investi- 

 gation reveal matters of deeper and wider interest, but in no direction do they bring 

 us to final limits in the field. The foremost workers take their turns in revising the 

 theories of their predecessors and in proposing new ones; and so, as we glance back- 

 ward, the most revered investigators appear as peerless pioneers of their time, and 

 their longest reaches of vision seem to be but primce vistce, and their greatest achieve- 

 ments but stepping-stones. 



In fact, it seems as if Darwin and Wallace, Nageli, Haeckel, Dohrn, Weismann, 

 de Vries, and a host of other investigators had grappled with an all-embracing 

 problem — -a problem that must engage the best energies of all the sciences for cen- 

 turies yet to come. 



The era now dawning presents us with three leading rival theories. From 

 Darwin and Wallace we have received the theory of natural selection, which has 

 been powerfully supported by Spencer, Huxley, Haeckel, Weismann, Dohrn, and 

 many others. This history and its triumphs are familiar history. 



In 1901 de Vries brought forward his famous mutation-theory, based upon "Ex- 

 periments and Observations on the Origin of Species in the Plant Kingdom." This 

 work of de Vries is truly a great achievement, rising above any other that has 

 appeared since Darwin's " Origin of Species." It is not only comprehensive in scope, 

 consistent in its logic, and charming in style, but it is also epoch-making in its 

 method of research. In this latter respect it sets an example which is having a 

 world-wide influence — emphasizing as it does the supreme importance of studying 

 living organisms, and of keeping observations and experiments running continu- 

 ously through a long sequence of generations. This is the method of the new era in 

 biology — steady, unbroken continuity in experiment under controlled culture. Here 

 the example of Mendel, de Vries, and a few others will be potent for centuries to 

 come. 



As to the real merit of the theory of mutation, only extended research can bring 

 a final decision. In dealing with such a theory, we must grasp clearly its fundamen- 

 tal conceptions. The whole superstructure stands or falls with them. 



The central foundation-idea of this mutation-theory is that of "unit-characters." 

 The species represents always a definite number of distinct unit-characters, each 

 as sharply defined and independent as are the elements of a chemical compound. 

 Consequently all upward progress in the organic world depends upon adding new 



1 This section of this chapter is the introduction and abstract (partly omitted) of a lecture delivered before the 

 Wisconsin Natural History Society by Professor Whitman at the meeting of December 20, 1906 (published in the 

 proceedings of that society, Vol. V, January 1907). A few slight changes in this manuscript seem to have been made 

 by the author after its publication; these changes are utilized here. The mutations described and figured in the final 

 part of the chapter have been arranged, and their description amplified from the records, by the editor. The best 

 cases of "mutation" observed and studied by Whitman belong to the period following the date of the above address. 

 These later studies on mutation reinforce and confirm the conclusions formed from the earlier studies. — Ed. 



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