Griffith : "Reve;rsion" in Prickly Pfars 225 



desirable. It is well known that lack the writer to point to the origin of the 



of spines is also a character which can spineless species of the so-called fitus- 



be maintained by vegetative propaga- indica group from the spiny ones, the 



tion, but being usually of shght variation spineless forms being the result of a 



is not as striking as the case mentioned long series of selection, both upon this 



of variation in an opposite direction, continent and in the Mediterranean 



This phenomenon is an important one, region, subsequent to their introduction 



for it furnishes a possible suggestion there. The striking variation of certain 



regarding the origin of the spineless spineless forms to a spiny condition is 



varieties. looked upon as a reversion to an original 



Both of these variations appear to type. 



Variation by Loss of Inhibitors 



A hypothesis to explain variation by the appearance of new dominant characters 

 as due to the loss of some single inhibiting factor, is put forward by William Bateson, 

 director of the John Innes Horticultural Institution at Merton, Surrey, England, 

 and the most distinguished exponent of Mendelism in England, in an address 

 before the seventeenth International Congress of Medicine, reprinted in the 

 Lancet. 



"We have been accustomed," he remarks, "to speak of characters as added 

 to or subtracted from the sum total of an individual composition, but as to the 

 actual origin of new dominants there is very little contemporary evidence. 



'•' In the case of those animals, such as the fowl, the wild original of which we 

 think we know, many factors exist in our domesticated breeds which are not 

 possessed by any of the wild species. No wild species, for example, has the com- 

 plicated combs that are possessed by our domestic breeds. None has the dominant 

 white color of the leghorn; and many other such instances might be given. How 

 have these elements been added to the composition of the fowl? 



"... but for one feature in the descent of dominants we might be tempted 

 to suggest that they also arose through the introduction of some element from 

 without into the system. I see no a priori impossibility in such a belief, but in 

 these dominants we know that the distribution among the germ-cells is approxi- 

 mately symmetrical, and nothing that we know of animals or plants justifies the 

 suggestion that a foreign element can be so treated in gameto-genesis. Perverse 

 as such a suggestion may appear, I do not think we should close our minds to the 

 possibility that these dominants arise by a process of some inhibiting factor. 

 Until we have some far more direct method of recognizing the presence of factors 

 this suggestion cannot be positively gainsaid." 



The Importance of Genetics 



Evolution, selection, heredity, environment, differential fertility, are not mere 

 vague terms of biological science having no application to htmian life. On their 

 right understanding depends the stability or collapse of human society in general 

 and of our nation in particular. — Karl Pearson: Nature and Nurture (1910). 



