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THE AMEBIC AN NATUEALIST [Vol. XLVI 



long we floundered helplessly in the quicksand of un- 

 clearness and complexity; now that we recognize our 

 study to be the history of any inheritable trait we move 

 on surer ground. And so, in general, progress is to be 

 made in the future by careful attention to the evolution 

 of characters. 



The second change in the formulation of the problem 

 that is due to the modern study of heredity is that we no 

 longer consider even the character as the ultimate unit 

 of evolution, but regard it rather as a product of such a 

 unit. For the character is, in some way or another, de- 

 termined by the conditions in or the constitution of the 

 germ-plasm and these conditions and this constitution, 

 though very different from the adult characters, are 

 their germinal representatives; and these germinal rep- 

 resentatives are the real units to be studied. Thus we 

 do not to-day formulate our problem as the evolution of 

 man, or of a blue-eyed man, but ask how the determiner 

 for brown-eye became lost from the germ-plasm. So, in 

 general, the problem of evolution is formulated as that 

 of the history of the germinal determiners of characters. 



Besides formulating more precisely the problem of 

 evolution, modern studies have discovered certain 

 methods of evolution which were not appreciated a 

 decade ago. First, we have come to realize that, though 

 not uniformly, yet to a surprising degree, characteristics 

 are independent of one another and, hence, that their 

 determiners in the germ-plasm are commonly not bound 

 together. The evidence for this is found in the breeding 

 experiments that have been performed on scores of 

 species of animals and plants, both feral and domesti- 

 cated. Breeders have taken advantage of this independ- 

 ence to create almost any desired combination of known 

 characters. Thus, in poultry the single pea or rose 

 comb may be combined with a black, white or game 

 plumage, with or without unfeathered shanks. The 

 shepherd's purse that grows by the roadside may be 

 made with either of two forms of capsules combined with 



