Seite - 386 - in The Origin of Species

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 factmore 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