374 THE GRAMMAR OF SCIENCE 



ceptions. Biologists, even as physicists have done, must 

 throw aside merely verbal descriptions and seek in future 

 quantitative precision for their ideas. 



§ 2. — Evolution 



If we look around us we see an immense variety 

 of living forms, and this immense variety is daily being 

 supplemented by the discovery of hitherto unrecorded 

 types either extant or extinct. The field naturalist, the 

 laboratory worker, and the palaeontologist are continually 

 bringing to our notice organic forms which have not 

 hitherto been observed. Under what formula shall we 

 economise thought when we attempt to describe scienti- 

 fically this vast field ? Now we have seen that geologist 

 and physicist both agree in asserting a want of stability in 

 the present inorganic conditions of the earth ; they best 

 resume its present state by giving to the earth a history, 

 during which it has passed through a wide range of 

 physical changes. These physical changes are not con- 

 sistent with the permanence of organic forms as we now 

 know them (p. 347). Some organic forms may have been 

 possible with the inorganic environment of thirty to fifty 

 million years ago, all were certainly not possible. Hence 

 if we are to have a causal account of living forms 

 as we have a causal account of their physical 

 environment, we must describe how they appeared after 

 the development of the fitting environment. If we agree 

 not to seek ^ an " ultra-scientific cause " (p. 352), i.e. if we 

 admit that a science of living forms is possible, then we 

 must seek our causes (p. 130) in antecedent phenomena, 

 either in organic phenomena or inorganic phenomena, or 

 in a combination of both. A causal description of the 



1 The causal description of the physicist, the physical evolution of the earth, 

 is now generally accepted in broad outline as a reasonable account. Yet it 

 explaitis nothing ; were it absolutely complete, and it is very far from that, it 

 would be merely a mechanical description such as Laplace imagined (p. 298). 

 An " ultra-scientific cause" might have intervened anywhere, "created" the 

 complex anywhere in its evolution, but such a " cause " would not in the least 

 invalidate the scientific formula. There is just as much reason for putting on 

 one side all "ultra-scientific causes" in biology as in physics (pp. 352-356). 



