PRESENT PROBLEMS 571 



Hubrecht, 1 and of the more recent references of Bateson 2 in his Brit- 

 ish Association address. That saltation is a constant phenomenon in 

 nature, a vera causa of evolution, no one can longer deny. Bateson 

 shows that it harmonizes with Mendel's conceptions of heredity, and 

 it may be regarded as par excellence the contribution of the experi- 

 mental method. 



Similarly, I regard mutation as a quite distinct phenomenon, and as 

 par excellence the contribution of the paleontological method; it is 

 the gradual rise of new adaptive characters neither by the selection of 

 accidental variations nor by saltation, but by origin in an obscure and 

 almost invisible form, followed by direct increase and development in 

 successive generations until a stage of actual usefulness is reached, 

 where perhaps selection may begin to operate. While clearly setting 

 forth the difficulties, I at one time attributed definite variation or 

 mutation to Lamarck's principle of the inherited effects of habit 

 as the only assignable cause; subsequently I realized that it was not 

 explainable by the Lamarckian hypothesis. 



I then attributed it to an unknown law of evolution, and there I be- 

 lieve it rests to-day, namely, as a process of which we do not know 

 the cause. Still more recently, however, comes the discovery that 

 original kinship is, partly at least, a control-principle. For example, 

 in the descent of independent stocks of hornless animals arising from 

 a common stock, rudimentary horn-cores are found to appear inde- 

 pendently in exactly the same region of the skull, indicating a kind 

 of predetermination in the stock, or- potential of similar evolutions. 

 The facts on which this law of mutation, properly called, rests have 

 been misunderstood, totally denied, or explained away by selectionists 

 as survivals of favorable out of indiscriminate variations. Even my 

 colleague, Scott, has identified these phenomena with the saltations of 

 De Vries. Nevertheless, I regard the genesis of new adaptive charac- 

 ters from almost imperceptible beginnings as a vera causa, and as one 

 of the greatest problems we have to solve. 



That a natural solution will be found goes without saying, although 

 this principle, as stated, is undoubtedly of a teleological nature. Its 

 philosophical bearings are of far-reaching importance. Just as we 

 demand a continent to transfer land animals from Australia to South 

 America, so we demand a natural law to explain these facts. 



The creative factors of fitness cooperating with selection, which, 

 in my judgment, are now well demonstrated, reside either primarily 



1 A. A. W. Hubrecht, Hugo De Vries's Theory of Mutations, The Popular Science 

 Monthly, vol. LXV, no. 3, July, 1904, pp. 205-228. 



2 W. Bateson. See Report of the British Association for the Advancement of 

 Science, Cambridge meeting, 1904; (with Miss E. R. Saunders) Reports to the 

 Evolution Committee of the Royal Society, 1902. [Gives summary of Mendel's 

 life and work.] 



3 H. F. Osborn, Recent Zoopaleontology, Science, 1905, N. S. vol. xxi, no. 530, 

 pp. 315-316. 



