Origin of Species Variorum

Comparison with 1866

in their own class, might beat the cephalopods or highest molluses; 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. Besides 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 distant periods— though undoubtedly this is one and perhaps the most important element in striking a balance— but we ought to compare all the members, high and low, at the two periods. At an ancient epoch the highest and lowest molluses, namely, cephalopods and brachiopods, swarmed in numbers: at the present time both these orders have been greatly reduced, whereas other orders, intermediate in grade of organisation, have been largely increased; consequently some naturalists have maintained that molluses were formerly more highly developed than at present; but a stronger case can be made out on the other side, by considering the vast reduction at the present day of the lowest molluses, more especially as the existing cephalopods, though so few in number, are more highly organised than their ancient representatives. We ought also to consider the relative proportional numbers of the high and low classes in the population of the world at any two periods: if, for instance, at the present day there be fifty thousand kinds of vertebrate animals, and if we knew that at some former period only ten thousand kinds had existed, we ought to look at this increase in number of the highest class, which implies a great displacement of lower forms, as a decided advance in the organisation of the world, whether the higher or the lower vertebrata had thus largely increased. We can thus see how hopelessly difficult it will apparently for ever be to compare with perfect fairness, under such extremely complex relations, the standard of organisation of the imperfectly-known faunas of successive periods of the earth's history.

We shall appreciate under one important point of view this difficulty the more clearly, by looking to the case of certain existing faunas and floras. From the extraordinary manner in which European productions have recently spread over New Zealand, and have seized on places which must have been previously occupied, we must believe, that if all the animals and plants of Great Britain were set free in New Zealand, in the course of time a multitude of British forms would become thoroughly naturalized there, and would exterminate many of the natives. On the other hand, from the progress of this displacement in New Zealand, and from hardly a single inhabitant of the southern hemisphere having become wild in any part of Europe, we may well doubt, if all the productions of New Zealand were set free in Great Britain, whether any considerable number would be enabled to seize on places now occupied by our native plants and animals. Under this point of view, the productions of Great Britain may be said to be higher than those of New Zealand. Yet the

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. Besides 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 to compare all the members, high and low, at the two periods. At an ancient epoch the highest and lowest molluscoidal animals, namely, cephalopods and brachiopods, swarmed in numbers; at the present time both groups are greatly reduced, whilst others, .. intermediate in .. organisation, have largely increased; consequently some naturalists .. maintain that molluscs were formerly more highly developed than at present; but a stronger case can be made out on the opposite side, by considering the vast reduction of brachiopods, and the fact that our existing cephalopods, though .. few in number, are more highly organised than their ancient representatives. We ought also to compare the relative proportional numbers at any two periods of the high and low classes throughout the world: if, for instance, at the ... present day .. fifty thousand kinds of vertebrate animals exist, and if we knew that at some former period only ten thousand kinds .. existed, we ought to look at this increase in number in the highest class, which implies a great displacement of lower forms, as a decided advance in the organisation of the world. .. .. .. .. .. .. .. .. .. .. .. We .. thus see how hopelessly difficult it is to compare with perfect fairness, under such extremely complex relations, the standard of organisation of the imperfectly-known faunas of successive periods. .. .. .. ..

We shall appreciate ... this difficulty .. more clearly, by looking to ... certain existing faunas and floras. From the extraordinary manner in which European productions have recently spread over New Zealand, and have seized on places which must have been previously occupied by the indigenes, we must believe, that if all the animals and plants of Great Britain were set free in New Zealand, ... a multitude of British forms would in the course of time become thoroughly naturalised there, and would exterminate many of the natives. On the other hand, from the fact that hardly a single inhabitant of the southern hemisphere has become wild in any part of Europe, we may well doubt whether, if all the productions of New Zealand were set free in Great Britain, .. any considerable number would be enabled to seize on places now occupied by our native plants and animals. Under this point of view, the productions of Great Britain stand much higher in the scale than those of New Zealand. Yet the