72 FOOT-NOTES TO EVOLUTION. 



proof, insusceptible of refutation. The argument for.it 

 is chiefly this : Life exists on a globe once lifeless. How 

 did life begin ? If not through spontaneous generation, 

 how did it come ? Must it not have been by the opera- 

 tion of those laws and forces which through all time 

 change lifeless into living matter ? Very likely, but we 

 do not know. We know nothing whatever of such laws 

 and forces, and we gain nothing by veiling our ignorance 

 under a philosophical necessity. 



Moreover, if spontaneous generation occurs as a re- 

 sultant of any forces, like forces would produce it again. 

 W T e have never known it to occur. Should it occur, the 

 organisms thus produced would have no bonds of blood 

 relationship with those already in existence. With these 

 they should show no homology, as they could have no 

 inheritance in common. But all known organisms have 

 common homologies. The factors of organic evolu- 

 tion are essentially the same for all. The unity of life 

 amid all its diversity seems to point to origin from a 

 common stock. If not from one stock, the lines of 

 division between one and another are hidden from us. 

 The study of embryology breaks down the time-honoured 

 branch lines of vertebrates, articulates, molluscs, and 

 radiates. The groups of animals are more numerous, 

 more complex, and more intertangled than Cuvier and 

 Agassiz thought. The number of primary branches of 

 animals or plants is uncertain, their boundaries unde- 

 fined. 



If spontaneous generation exists, it is a factor in 

 evolution. If it is a factor, our explanation of the 

 meaning and nature of homology must be fundamentally 

 changed. But it may be that it should be changed. We 

 can not show that spontaneous generation does not 

 exist. All we know is that we have no means of recog- 

 nising it. If there is now spontaneous generation of 



