532 THE EVOLUTION OF LIFE. 



that such a factor is at work. To him we owe due appreciation 

 of the fact that natural selection is capable of producing fit- 

 ness between organisms and their circumstances. He has 

 worked up an enormous mass of evidence showing that this 

 " preservation of favoured races in the struggle for life/' is an 

 ever-acting cause of divergence among organic forms. He has 

 traced out the involved results of the process with marvellous 

 subtlety. He has shown how hosts of otherwise inexplicable 

 facts, are accounted for by it. In brief, he has proved that 

 the cause he alleges is a true cause; that it is a cause which 

 we see habitually in action; and that the results to be in- 

 ferred from it are in harmony with the phenomena which 

 the Organic Creation presents, both as a whole and in its 

 details. Let us glance at a few of the more important inter- 

 pretations which the hypothesis furnishes. 



A soil possessing some ingredient in unusual quantity, 

 may supply to a plant an excess of the matter required for 

 certain of its tissues ; and may cause all the parts formed of 

 such tissues to be abnormally developed. Suppose that 

 among these are the hairs clothing its surfaces, including 

 those which grow on its seeds. Thus furnished with some- 

 what longer fibres, its seeds, when shed, are carried a little 

 further by the wind before they fall to the ground. The 

 plants growing from them, being rather more widely dis- 

 persed than those produced by other individuals of the same 

 species, will be less liable to smother one another ; and a 

 greater number may therefore reach maturity and fructify. 

 Supposing the next generation subject to the same peculiarity 

 of nutrition, some of the seeds borne by its members will not 

 simply inherit this increased development of hairs, but will 

 carry it further; and these, still more advantaged in the 

 same way as before, will, on the average, have still more 

 numerous chances of continuing the race. Thus, by the sur- 

 vival, generation after generation, of those possessing these 

 longer hairs, and the inheritance of successive increments of 

 growth in the hairs, there may result a seed deviating greatly 



