w—aumammm 



NATUKAL SELECTION. 13 



extended, — that is, in determining from how many progenitors 

 the inhabitants of the world have descended, — we may con- 

 clude that at least all the members of the same class have 

 descended from a single ancestor. A number of organic beings 

 are included in the same class, because they present, inde- 

 pendently of their habits of life, the same fundamental type 

 of structure, and because they graduate into each other. 

 Moreover, members of the same class can in most cases be 

 shown to be closely alike at an early embryonic age. These 

 facts can be explained on the belief of their descent from a 

 common. form; therefore it may be safely admitted that all 

 the members of the same class have descended from one pro- 

 genitor. But as the members of quite distinct classes have 

 something in common in structure and much in common in 

 constitution, analogy and the simplicity of the view would lead 

 us one step further, and to infer as probable that all living 

 creatures have descended from a single prototype. 

 ^ I hope that the reader will pause before coming to any 

 final and hostile conclusion on the theory of natural selec- 

 tion. It is the facts and views to be hereafter given which 

 have convinced me of the truth of the theory. The reader 

 may consult my < Origin of Species,' for a general sketch 

 of the whole subject ; but in that work he has to take many 

 statements on trust. In considering the theory of natural 

 selection, he will assuredly meet with weighty difficulties, but 

 these difficulties relate chiefly to subjects— such as the degree 

 of perfection of the geological record, the means of distribu- 

 tion, the possibility of transitions in organs, &c— on which 

 we are confessedly ignorant; nor do we know how ignorant 

 we are. If we are much more ignorant than is generally 

 supposed, most of these difficulties wholly disappear. Let the 

 reader reflect on the difficulty of looking at whole classes 

 of facts from a new point of view. Let him observe how 

 slowly, but surely, the noble views of Lyell on the gradual 

 changes now in progress on the earth's surface have been ac- 

 cepted as sufficient to account for all that we see in its past, 

 history. The present action of natural selection may seem 

 more or less probable ; but I believe in the truth of the theory, 



