386 ORIGIN OF SPECIES 



had then reached. When advanced up to any given point, 

 there is no necessity, on the theory of natural selection, for 

 ) their further continued progress; though they will, during 

 each successive age, have to be slightly modified, so as to 

 hold their places in relation to slight changes in their condi- 

 tions. The foregoing objections hinge on the question 

 whether we really know how old the world is, and at what 

 period the various forms of life first appeared; and this may 

 well be disputed. 



The problem whether organisation on the whole has ad- 

 vanced is in many ways excessively intricate. The geological 

 record, at all times imperfect, does not extend far enough 

 back, to show with unmistakeable clearness that within the 

 known history of the world organisation has largely ad- 

 vanced. Even at the present day, looking to members of the 

 same class, naturalists are not unanimous which forms ought 

 to be ranked as highest: thus, some look at the selaceans or 

 sharks, from their approach in some important points of 

 structure to reptiles, as the highest fish; others look at the 

 teleosteans as the highest. The ganoids stand intermediate 

 between the selaceans and teleosteans; the latter at the 

 present day are largely preponderant in number; but for- 

 merly selaceans and ganoids alone existed; and in this case, 

 according to the standard of highness chosen, so will it be 

 said that fishes have advanced or retrograded in organisa- 

 tion. To attempt to compare members of distinct types in 

 the scale of highness seems hopeless ; who will decide whether 

 a cuttle-fish be higher than a bee — that insect which the 

 great Von Baer believed to be "in fact more highly organised 

 than a fish, although upon another type"? In the complex 

 struggle for life it is quite credible that crustaceans, not very 

 high in their own class, might beat cephalopods, the highest 

 molluscs; and such crustaceans, though not highly developed, 

 would stand very high in the scale of invertebrate animals, if 

 judged by the most decisive of all trials — the law of battle. 

 Beside these inherent difficulties in deciding which forms 

 are the most advanced in organisation, we ought not solely 

 to compare the highest members of a class at any two 

 periods — though undoubtedly this is one and perhaps the 

 most important element in striking a balance — but we ought 



