W. B. Scott — Variations and Mutations. 359. 



between the structure, the instincts or other elements which 

 compose the mechanism of the offspring and those which were 

 proper to the parent, the name variation lias been given " (p. 3). 

 In most species, while no two individuals are exactly alike, the 

 greater part of them resemble one another very closely and 

 thus make a normal from which few individuals depart very 

 widely ; the magnitude of such departures is in general pro- 

 portionate to their infrequency. The phylogeny of a species 

 is given by the shifting of this normal, or center of " organic 

 stability" (to use G-alton's phrase) not in all the variations of 

 the successive species, which are more or less different in 

 every generation. While the species remains stable, the 

 variations tend to balance and correct one another through the 

 operation of what Galton has called the regression to medi- 

 ocrity, while a material change in the position of the normal, 

 either sudden or gradual, results in the formation of a new 

 species. The fact that the variations of the species may be so 

 arranged as to form a complete transition between them, does 

 not, as Bateson very pertinently shows, prove that the actual 

 change was along the lines indicated by such a selected series 

 of variations. 



Turning now to the examination of Bateson's results, we 

 find that the one upon which he lays most stress is the proof of 

 discontinuity in variation. " The existence of discontinuity in 

 variation is therefore a final proof that the accepted hypothesis 

 is inadequate .... For if distinct and ' perfect ' varieties 

 may come into existence discontinuously, may not the discon- 

 tinuity of species have had a similar origin ? If we accept the 

 postulate of common descent, this expectation is hard to resist. 

 In accepting that postulate it was admitted that the definite- 

 ness and discontinuity of species depends upon the greater 

 permanence or stability of certain terms in the series of 



descent. The evidence of variation suggests in brief 



that the discontinuity of species results from the discontinuity 

 of variation. This suggestion is in a word the one clear and 

 positive indication born on the face of the facts. Though as 

 yet it is but an indication, there is scarcely a problem in the 

 comparison of structures where it may not be applied with 

 profit." (p. 568). 



The mammalian phyla do not support this view of discon- 

 tinuity in the origin of species and genera. Remembering 

 that the significant fact in the history of a group is not so 

 much the character of its variations at any one stage as the 

 gradually shifting positions successively occupied by the 

 normal or center of stability, we find that any mammalian 

 series at all complete, such as that of the horses, is remarkably 

 continuous and that the progress of discovery is steadily filling 



