1.1 THE CHOICE OF AN EXAMPLE 63 



ations being accumulated by natural selection. He was 

 not ignorant of the facts of sudden variation; but he thought 

 these "sports," as he called them, were only monstrosities 

 incapable of perpetuating themselves; and he accounted 

 for the genesis of species by an accumulation of insensible 

 variations. 1 Such is still the opinion of many naturalists. 

 It is tending, however, to give way to the opposite idea 

 that a new species comes into being all at once by the 

 simultaneous appearance of several new characters, all 

 somewhat different from the previous ones. This latter 

 hypothesis, already proposed by various authors, notably 

 by Bateson in a remarkable book,' has become deeply 

 significant and acquired great force since the striking ex- 

 periments of Hugo de Vries. This botanist, working on 

 the (Enothera Lamar ckiana, obtained at the end of a few 

 generations a certain number of new species. The theory 

 he deduces from his experiments is of the highest interest. 

 Species pass through alternate periods of stability and 

 transformation. When the period of "mutability" occurs, 

 unexpected forms spring forth in a great number of differ- 

 ent directions. 3 — We will not attempt to take sides be- 

 tween this hypothesis and that of insensible variations. 

 Indeed, perhaps both are partly true. We wish merely 

 to point out that if the variations invoked are accidental, 

 they do not, whether small or great, account for a similar- 

 ity of structure such as we have cited. 



Let us assume, to begin with, the Darwinian theory of 

 insensible variations, and suppose the occurrence of small 

 differences due to chance, and continually accumulating. 



1 Darwin, Origin of Species, chap. ii. 



1 Bateson, Materials for the Study of Variation, London, 1894, es- 

 pecially pp. 567 ff. Cf. Scott, "Variations and Mutations" (American 

 Journal of Science, Nov. 1894). 



• De Vries, Die Mutationstheorie, Leipzig, 1901-1903. Of., by the 

 same author, Species and Varieties, Chicago, 1905. 



