96 Heredity and Variation in Modern Lights 
dominant, and at some moment since Gallus bankiva was domesticated, 
the 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. 
With 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 varictés, mais le hazard ou Fart les 
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 wrote”: “Das Gesetz der Vererbung 
ist noch nicht erkannt; der Apfel ist noch nicht vom Baum der 
Erkenntniss gefallen, welcher, der Sage nach, Newton auf den 
1 T have in view, for example, the marvellous and specific phenomena of regeneration, 
and those discovered by the students of ‘‘Entwicklungsmechanik.” 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 in 
mere parodies of scientific reasoning. 
2 Vortrige tiber Viehzucht und Rassenerkenntniss, p. 120, Berlin, 1872. 
