Prof. Huxley on the Animals between Birds and Rejptiles. 67 



immeasurable time, by the operation of causes more or less similar 

 to those which are at work at the present day. 



Perhaps this doctrine of evolution is not maintained consciously 

 and in its logical integrity by a very great number of persons *. But 

 many hold particular applications of it without committing them-^ 

 solves to the whole; and many, on the other hand, favour the ge-^. 

 neral doctrine without giving an absolute assent to its particular 

 applications. 



Thus, one who adopts the nebular hypothesis in astronomy, or is 

 a uniformitarian in geology, or a Darwinian in biology, is so far an 

 adherent of the doctrine of evolution. 



And, as I can testify from personal experience, it is possible to 

 have a complete faith in the general doctrine of evolution and yet to 

 hesitate in accepting the nebular, or the uniformitarian, or the Dar- 

 winian hypotheses in all their integrity and fulness ; for many of 

 the objections which are brought against these various hypotheses 

 affect them only, and, even if they be valid, leave the general doc- 

 trine of evolution untouched. 



On the other hand, it must be admitted that some arguments which 

 are adduced against particular forms of the doctrine of evolution 

 would very seriously affect the whole doctrine if they were proof 

 against refutation. 



For example, there is an objection which I see constantly and 

 confidently urged against Mr. Darwin's views, but which really strikes 

 at the heart of the whole doctrine of evolution, so far as it is applied 

 to the organic world. 



It is admitted on all sides that existing animals and plants are 

 marked out by natural intervals into sundry very distinct groups : 

 insects are widely different from fish, fish from reptiles, reptiles 

 from mammals, and so on. And out of this fact arises the very 

 pertinent objection. How is it, if all animals have proceeded by 

 gradual modification from a common stock, that these great gaps 

 exist ? 



We, who believe in evolution, reply that these gaps were once 

 non-existent ; that the connecting forms existed in previous epochs 

 of the world's history, but that they have died out. 



I^aturally enough, then, we are asked to produce these extinct 

 forms of life. Among the innumerable fossils of all ages which 

 exist, we are asked to point to those which constitute such connect- 

 ing forms. 



Our reply to this request is, in most cases, an admission that such 

 forms are not forthcoming ; and we account for this failure of the 

 needful evidence by the known imperfection of the geological record. 

 We say that the series of formations with which we are acquainted 

 is but a small fraction of those which have existed, and that between 

 those which we know there are great breaks and gaps. 



* The only complete and systematic statement of the doctrine with 

 which I am acquainted is that contained in Mr. Herbert Spencer's ' Sys- 

 tem of Philosophy/ a work which should be carefully studied by all who 

 desire to know whither scientific thought is tending. 



5* 



