NATURAL SELECTION. 93 



the other, selection does nothing without Tariability, and 

 this depends in some manner on the action of the sur- 

 rounding circumstances in the organism. I have, also, 

 often personified the word Nature ; for I have found it 

 difficult to avoid this ambiguity ; but I mean by nature 

 only the aggregate action and product of many natural 

 laws, and by laws only the ascertained sequence of events. 



.AN INVENTED HYPOTHESIS. 



Animals and ^° scientific investigations it is permitted 

 Plants, vol. i, to invent any hypothesis, and if it explains 

 page 9. various large and independent classes of facts 



it rises to the rank of a well-grounded theory. The un- 

 dulations of the ether and even its existence are hypo- 

 thetical, yet every one now admits the undulatory theory 

 of light. The principle of natural selection may be looked 

 at as a mere hypothesis, but rendered in some degree 

 probable by what we positively know of the variability of 

 organic beings in a state of nature — ^by what we positively 

 know of the struggle for existence, and the consequent 

 almost inevitable preservation of favorable variations—^ 

 and from the analogical formation of domestic races. 

 !Now, this hypothesis may be tested — and this seems to me 

 the only fair and legitimate manner of considering the 

 whole question — by trying whether it explains several 

 large and independent classes of facts ; such as the geo- 

 logical succession of organic beings, their distribution in 

 past and present times, and their mutual afiBnities and 

 homologies. If the principle of natural selection does 

 explain these and other large bodies of facts, it ought to 

 be received. On the ordinary view of each species hav- 

 ing been independently created, we gain no scientific ex- 

 planation of any one of these facts. We can only say that 



