The Theory of Natural Selection. 283 



expanding an illustration which, I believe, was first 

 used by Professor Huxley. If, when the tide is out, we 

 see lying upon the shore a long line of detached sea- 

 weed, marking the level which is reached by full tide, 

 we should be free to conclude that the separation of 

 the sea-weed from the sand and the stones was due 

 to the intelligent work of some one who intended to 

 collect the sea-weed for manure, or for any other pur- 

 pose. But, on the other hand, we might explain the 

 fact by a purely physical cause namely, the separa- 

 tion by the sea-waves of the sea-weed from the sand 

 and stones, in virtue of its lower specific gravity. Now, 

 thus far the fact would be explained equally well by 

 either hypothesis ; and this fact would be the fact of 

 selection. But whether we yielded our assent to the 

 one explanation or to the other would depend upon a 

 due consideration of all collateral circumstances. The 

 sea-weed might not be of a kind that is of any use to 

 man ; there might be too great a quantity of it to 

 admit of our supposing that it had been collected by 

 man ; the fact that it was all deposited on the high- 

 water-mark would in itself be highly suggestive of the 

 agency of the sea ; and so forth. Thus, in such a case 

 any reasonable observer would decide in favour of the 

 physical explanation, or against the teleological one. 



Now the question whether organic evolution has 

 been caused by physical agencies or by intelligent 

 design is in precisely the same predicament There 

 can be no logical doubt that, theoretically at all events, 

 the physical agencies which the present chapter is con- 

 cerned with, and which are conveniently summed up in 

 the term natural selection, are as competent to produce 

 these so-called mechanical contrivances, and the other 



