50 LECTURES ON EVOLUTION m 



of things has had only a limited duration ; and 

 that, at some period in the past, a condition of 

 the world, essentially similar to that which we now 

 know, came into existence, without any precedent 

 condition from which it could have naturally pro- 

 ceeded. The assumption that successive states of 

 Nature have arisen, each without any relation of 

 natural causation to an antecedent state, is a 

 mere modification of this second hypothesis. 



The third hypothesis also assumes that the pres- 

 ent state of things has had but a limited dura- 

 tion ; but it supposes that this state has been 

 evolved by a natural process from an antecedent 

 state, and that from another, and so on ; and, on 

 this hypothesis, the attempt to assign any limit to 

 the series of past changes is, usually, given up. 



It is so needful to form clear and distinct notions 

 of what is really meant by each of these hypotheses 

 that I will ask you to imagine what, according to 

 each, would have been visible to a spectator of 

 the events which constitute the history of the 

 earth. On the first hypothesis, however far back 

 in time that spectator might be placed, he would 

 see a world essentially, though perhaps not in all 

 its details, similar to that which now exists. The 

 animals which existed would be the ancestors of 

 those which now live, and similar to them ; the 

 plants, in like manner, would be such as we know ; 

 and the mountains, plains, and waters would fore- 

 shadow the salient features of our present land 



