THE PHENOMENA OF ORGANIC NATURE. 131 



other known causes are competent to produce these 

 phenomena. If we can succeed in satisfying these 

 three conditions, we shall have demonstrated our hypo- 

 thesis ; or rather I ought to say, we shall have proved 

 it as far as certainty is possible for us ; for, after all, 

 there is no one of our surest convictions which may not 

 be upset, or at any rate modified by a further accession 

 of knowledge. It was because it satisfied these con- 

 ditions that we accepted the hypothesis as to the dis- 

 appearance of the tea-pot and spoons in the case I sup- 

 posed in a previous lecture ; we found that our hypo- 

 thesis on that subject was tenable and valid, because 

 the supposed cause existed in nature, because it was 

 competent to account for the phenomena, and because 

 no other known cause was competent to account for 

 them ; and it is upon similar grounds that any hypo- 

 thesis you choose to name is accepted in science as 

 tenable and valid. 



What is Mr. Darwin's hypothesis ? A I apprehend 

 it — for I have put it into a shape more convenient for 

 common purposes than I could find verbatim in his book 

 — as I apprehend it, I say, it is, that all the phenome- 

 na of organic nature, past and present, result from, 

 or are caused by, the inter-action of those properties of 

 organic matter, which we have called Atavism and 

 Variability, with the Conditions of Existence ; or, 

 in other words, — given the existence of organic matter, 

 its tendency to transmit its properties, and its tendency 

 occasionally to vary ; and, lastly, given the conditions 

 of existence by which organic matter is surrounded — 

 that these put together are the causes of the Present 

 and of the Past conditions of Organic Nature. 



Such is the hypothesis as I understand it. Now 



