An Introduction to a Biology 



teleological in any sense of the word as anything can be 

 imagined to be). Above all, cases of continuous variation 

 can be described by curves of error, a fact which seems to 

 me to have a very deep meaning. Discontinuous variation 

 is the quality which animals and plants possess of giving 

 rise, from time to time, to offspring bearing characters 

 specifically different from those of their parents : in fact, 

 by some these offspring are termed " sports." This " sport " 

 is a new species : that is to say (to use Bateson's words), 

 " Variation, in fact, is evolution " ('99, p. 6) ; but while 

 this can be said of discontinuous, continuous variation is 

 merely the material upon which natural selection operates 

 (if we may thus personify that process). From this it follows 

 that according to the latter view it is impossible to say 

 where one species begins and the other ends ; but that 

 according to the former view there is no such difficulty. 



Continuous variation may be looked upon as normal, 

 while discontinuous may be regarded as abnormal ; but 

 this aspect of the matter is perhaps only .justifiable as a 

 help to understanding the difference. For if species have 

 arisen by discontinuous variation it is hardly fair to call 

 it abnormal. (Vide Ewart, '99, p. Ixxxiv.) 



The word " Variation " may represent an abstract or a 

 concrete thing : in the continuous sense it is usually a name 

 given to the whole phenomenon of variation : in the dis- 

 continuous, the so-called sport is often spoken of as "a 

 variation " (whereas a man with a cephalic index slightly 

 less than his neighbour's would hardly be). This twofold 

 use of the term conveniently recalls the two conceptions of 

 variation. 



(2) GALTON'S THEORY OF HEREDITY 



I refer to Galton's theory of heredity because I want to 

 show how the Mendelian theory differs from the statistical 

 conception of that phenomenon. Galton said : " The two 

 parents contribute between them on the average one-half, 



128 



