186 REPORT — 1875. 



cliiefly aifect life ; and to the local climate and conditions being compatible with 

 such immigration. 



For the explanation of these and other phenomena of organization and distri- 

 bution, the only direct evidence that observation can supply is that derived from 

 the mode of propagation of creatures now living ; and no other mode is known 

 than that which takes place by ordinary generation, through descent from parent 

 to offspring. 



It was left for the genius of Darwin to point out how the com-se of nature 

 as it now acts in the reproduction of living creatures, is sufficient for the inter- 

 pretation of what had previously been incomprehensible in these matters. He 

 showed how propagation by descent operates subject to the occurrence of certain 

 small variations in the offspring, and that the preservation of some of these 

 varieties to the exclusion of others follows as a necessary consequence when 

 the external conditions are more suitable to the preserved forms than to those lost. 

 The operation of these causes he called Natural Selection. Prolonged over a gi'eat 

 extent of time it supplies the long-sought key to the complex system of forms 

 either now living on the earth, or the remains of which are foimd in the fossil 

 state, and explains the relations among them, and the manner in which their 

 distribution has taken place in time and space. 



Thus we are brought to the conclusion that the directing forces which have been 

 efficient in developing the existing forms of life from those which went before 

 them, are those same successive external conditions, including both the forms of 

 land and sea and the character of the climate, which have already been showxi 

 to arise from the gi-adual modification of the material fabric of the globe as it 

 slowly attained to its present state. In each succeeding epoch, and in each 

 separate locality, the forms preserved and handed on to the future were deter- 

 mined by the general conditions of siu-face at the time and place ; and the 

 aggi'egate of successive sets of conditions over the whole eirth's sm-face has 

 determined the entire series of forms which have existed in the past and have 

 siu-vived till now. 



As we recede from the present into the past, it necessarily follows, as a 

 consequence of the ultimate f'ailm-e of all evidence as to the conditions of the past, 

 that positive testimony of the conformity of the facts with the principle of evo- 

 lution gradually diminishes, and at length ceases. In the same way positive evi- 

 dence of the continuity of action of all the physical forces of nature eventually fails. 

 But inasmuch as the e-vddence, so far as it can be procured, supports the belief in this 

 continuity of action, and as we have no experience of the contrary being possible, 

 the only justifiable conclusion is, that the production of life must have been going 

 on as we now Iniow it, without any intermission, from the time of its first appear- 

 ance on the earth. 



These considerations manifestly afford no sort of clue to the origin of life. They 

 only serve to take us back to a very remote epoch, when the living creatures 

 differed greatly in detail from those of the present time, but had such resem- 

 blances to them as to justify the conclusion that the essence of life then was the 

 same as now ; and through that epoch into an imlmown anterior period, during 

 which the possibility of life, as we understand it, began, and from which has 

 emerged, in a way that we cannot comprehend, matter with its properties, bound 

 together by what we call the elementary physical forces. There seems to be no 

 foundation in any observed fact for suggesting that the wonderful property which 

 we call life appertains to the combinations of elementary substances in association 

 with which it is exclusively foimd, otherwise than as all other properties appertain 

 to the particular forms or combinations of matter with which they are associated. 

 It is no more possible to say how originated or operates the tendency of some sorts 

 of matter to take the form of vapours, or fluids, or solid bodies, in all their various 

 shapes, or for the various sorts of matter to attract one another or combine, than it 

 is to explain the origin in certain forms of matter of the property we call life, or the 

 mode of its action. For the present, at least, we must be content to accept such 

 facts as the foundation of positive knowledge, and from them to rise to the appre- 

 hension of the means by which nature has reached its present state, and is ad- 

 vancing into an unknown futnre. 



