96 Heredity a7id Variation in Modem Lights 



dominant, and at some moment since Galliis hanldva was domesticated, 

 tlie element on which that special colour depends must have at least 

 once been formed in the germ-cell of a fowl ; but we need harder 

 evidence than any which has yet been produced before we can declare 

 that this novelty came through over-feeding, or change of climate, or 

 any other disturbance consequent on domestication. When we reflect 

 on the intricacies of genetic problems as we must now conceive them 

 there come moments when we feel almost thankful that the Mendelian 

 principles were unknown to Darwin. The time called for a bold 

 pronouncement, and he made it, to our lasting profit and delight. 

 AVith fuller knowledge we pass once more into a period of cautious 

 expectation and reserve. 



In every arduous enterprise it is pleasanter to look back at 

 difficulties overcome than forward to those which still seem insur- 

 mountable, but in the next stage there is nothing to be gained by 

 disguising the fact that the attributes of living things are not what 

 we used to suppose. If they are more complex in the sense that the 

 properties they display are throughout so regular^ that the Selection 

 of minute random variations is an unacceptable account of the origin 

 of their diversity, yet by virtue of that very regularity the problem is 

 limited in scope and thus simplified. 



To begin with, we must relegate Selection to its proper place. 

 Selection permits the viable to continue and decides that the non- 

 viable shall perish ; just as the temperature of our atmosphere 

 decides that no liquid carbon shall be found on the face of the earth : 

 but we do not suppose that the form of the diamond has been 

 gradually achieved by a process of Selection. So again, as the 

 course of descent branches in the successive generations, Selection 

 determines along which branch Evolution shall proceed, but it does 

 not decide what novelties that branch shall bring forth. ^^La Nature 

 contient le fonds de toutes ces varietes, mats le hazard ou I'art hs 

 mettent en oeuvre," as Maupertuis most truly said. 



Not till knowledge of the genetic properties of organisms has 

 attained to far greater completeness can evolutionary speculations 

 have more than a suggestive value. By genetic experiment, cytology 

 and physiological chemistry aiding, we may hope to acquire such 

 knowledge. In 1872 Nathusius wi-ote- : "Das Gesetz der Vererbung 

 ist noch nicht erkannt ; der Apfel ist noch nicht vom Baum der 

 Erkcnntniss gefallen, welcher, der Sage nach, Newton auf den 



1 I have in view, for example, the marvellous and specific phenomena of regeneration, 

 and those discovered by the students of " Entwicklungsmcchanik." The circumstances of 

 its occurrence here preclude any suggestion that this regularity has been brought about by 

 the workings of Selection. The attempts thus to represent the phenomena have resulted iu 

 mere parodies of scientific reasoning. 



' Vortriige uber Viehzucht und Rassenerkenntnis», p. 120, Berlin, 1872. 



