132 



THE GEOLOGIST. 



SOME REMARKS ON MR. DARWIN'S THEORY. 

 By Frederick Wollastoh Htjtton, E.G.S. 



I said that " all tlie years invent ; 

 Each month is various to present 

 The world with some development." — Tennyson. 



Although most of my readers will be perfectly acquainted with the 

 theory proposed by Mr. Darwin to account for the various forms of 

 life that we see on the globe, yet, for the sake of clearness, I will 

 briefly enunciate it. 



Mr. Darwin first shows that individuals of the same species vary 

 one with another. 



He then shows that, owing to the rapid increase of animal and vege- 

 table life, by which many more are born each year than can possibly 

 survive, there is a continual warfare going on among them for food 

 and other necessaries. This he calls the " struggle for life." 



He then shows that if any animal or plant should have, by varia- 

 tion, any organ or property so modified as to give it some advantage 

 over its fellows in the struggle for life, it will, as a general rule, live 

 longer and produce more offspring ; and these offspring will have a 

 tendency to inherit the organ or property modified in the same man- 

 ner : but if in one of these offspring the organ should be still further 

 modified, it will give him a like advantage over his brethren, and his 

 offspring again will have a tendency to reproduce the organ in its 

 more modified state ; and so on. This he calls "'Natural Selection." 



Mr. Darwin thinks that this, together with the minor causes of 

 habit, use and disuse, climate, &c, are sufficient to account for all the 

 various forms of organic life, by the gradual transmutation of one 

 species into another. 



As all naturalists allow that species vary, it seems that the difference 

 in i lie opinions of some of them on this subject arise on the question 

 of limits. Are these varieties of species limited, or are they unlimited ? 



A limiting value of a variable is a quantity to which the variable 

 may approach ever so near, but never reach ; if therefore it can be 

 shown that there is a limiting value to the variation of species, Mr. 

 I );invin's theory could not be extended beyond that limit. At present 

 no one 1ms been able to assign to it any limits at all ; in fact it will be a 

 very difficult thing to do so, for it would be of no use to prove that 

 any one organ of a particular animal could not change into the rare 

 organ of another particular animal, as it is never supposed that the 

 higher form of life has passed through every lower form ; for the same 

 reason thai the sap which nourishes one leaf of a tree has not passed 

 through all the other leaves. 



The way this question has generally been argued is, not by trying 

 to define any one strict limit beyond which variation cannot pass, but 



