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422 INDEPENDENT CREATION. CHAP. XXI.
cause, therefore, which has, as yet, been even conjecturally brought forward, to explain how, in the ordinary course of nature, a new specific form may be generated is, as Lamarck declared, ' variation,' and this has been rendered a far more probable hypothesis by the way in which Natural Selection is shown to give intensity and permanency to certain varieties.
When I formerly advocated the doctrine that species were primordial creations, and not derivative, I endeavoured to explain the manner of their geographical distribution, and the affinity of living forms to the fossil types nearest akin to them in the tertiary strata of the same part of the globe, by supposing that the creative power, which originally adapts certain types to aquatic and others to terrestrial conditions, has, at successive geological epochs introduced new forms best suited to each area and climate, so as to fill the places of those which may have died out.
In that case, although the new species would differ from the old (for these would not be revived, having been already proved by the fact of their extinction, to be incapable of holding their ground), still, they would resemble their predecessors generically. For, as Mr. Darwin states in regard to new races, those of a dominant type inherit the advantages which made their parent species flourish in the same country, and they likewise partake in those general advantages which made the genus to which the parent species belonged, a large genus in its own country.
We might, therefore, by parity of reasoning, have anticipated that the creative power, adapting the new types to the new combination of organic and inorganic conditions of a given region, such as its soil, climate, and inhabitants, would introduce new modifications of the old types,— marsupials,
CHAP. XXI. INDEPENDENT CREATION. 423
for example in Australia, new sloths and armadilloes in South America, new heaths at the Cape, new roses in the northern, and new calceolarias in the southern hemisphere. But to this line of argument Mr. Darwin and Dr. Hooker reply, that when animals or plants migrate into new countries, whether assisted by man, or without his aid, the most successful colonisers appertain by no means to those types which are most allied to the old indigenous species. On the contrary, it more frequently happens that members of genera, orders, or even classes, distinct and foreign to the invaded country, make their way most rapidly, and become dominant at the expense of the endemic species. Such is the case with the placental quadrupeds in Australia, and with horses and many foreign plants in the pampas of South America, and numberless instances in the United States and elsewhere, which might easily be enumerated. Hence, the transmutationists infer that, the reason why these foreign types, so peculiarly fitted for these regions have never before been developed there, is simply that they were excluded by natural barriers. But these barriers of sea, or desert, or mountain, could never have been of the least avail, had the creative force acted independently of material laws, or had it not pleased the Author of Nature that the origin of new species should be governed by some secondary causes analogous to those which we see preside over the appearance of new varieties, which never appear except as the offspring of a parent stock very closely resembling them.
424 THEORY OF TRANSMUTATION. CHAP. xxn.
OBJECTIONS TO THE HYPOTHESIS OF TRANSMUTATION CONSIDERED.
STATEMENT OF OBJECTIONS TO THE HYPOTHESIS OF TRANSMUTATION
THE BRACHIOPODA WHY THE GRADATIONAL FORMS, WHEN FOUND,
ARE NOT ACCEPTED AS EVIDENCE OF TRANSMUTATION — GAPS CAUSED
OF NORTH AMERICA, ASIA, AND EUROPE SPECD3S OF MAMMALIA,
THOUGH LESS PERSISTENT THAN THE MOLLUSCA, CHANGE SLOWLY
ARGUMENTS FOR AND AGAINST TRANSMUTATION DERIVED FROM THE
Theory of Transmutation—Absence of Intermediate Links.
THE most obvious and popular of the objections urged against the theory of transmutation may be thus expressed: If the extinct species of plants and animals of the later geological periods were the progenitors of the living species, and gave origin to them by variation and natural selection, where are all the intermediate forms, fossil and living, through which the lost types must have passed during their conversion into the living ones? And why do we not find almost everywhere passages between the nearest allied
CHAP. xxn. OBJECTIONS TO TRANSMUTATION. 425
species and genera, instead of such strong lines of demarcation, and often wide intervening gaps?
We may consider this objection under two heads: —
First, To what extent are the gradational links really wanting in the living creation or in the fossil world, and how far may we expect to discover such as are missing by future research?
Secondly, Are the gaps more numerous than we ought to anticipate, allowing for the original defective state of the geological records, their subsequent dilapidation, and our slight acquaintance with such parts of them as are extant, and allowing also for the rate of extinction of races and species now going on, and which has been going on since the commencement of the tertiary period?
First, As to the alleged absence of intermediate varieties connecting one species with another, every zoologist and botanist who has engaged in the task of classification has been occasionally thrown into this dilemma,—if I make more than one species in this group, I must, to be consistent, make a great many. Even in a limited region like the British Isles, this embarrassment is continually felt.
Scarcely any two botanists, for example, can agree as to the number of roses, still less as to how many species of bramble we possess. Of the latter genus, Rubus, there is one set of forms, respecting which it is still a question whether it ought to be regarded as constituting three species or thirty-seven. Mr. Bentham adopts the first alternative, and Mr. Babingtoh the second, in their well-known treatises on British plants.
We learn from Dr. Hooker that at the antipodes, both in New Zealand and Australia, this same genus Rubus is represented by several species rich in individuals and remarkable for their variability. When we consider how, as we extend our knowledge of the same plant over a wider area, new
426 DAVIDSON ON FOSSIL BRACHIOPODA. CHAP. XJtn.
geographical varieties commonly present themselves, and then endeavour to imagine the number of forms of the genus Rubus which may now exist, or probably have existed, in Europe and in regions intervening between Europe and Australia, comprehending all which may have flourished in tertiary and post-tertiary periods, we shall perceive how little stress should be laid on arguments founded on the assumed absence of missing links in the flora as it now exists.
If in the battle of life the competition is keenest between closely allied varieties and species, as Mr. Darwin contends, many forms can never be of long duration, nor have a wide range, and these must often pass away without leaving behind them any fossil memorials. In this manner we may account for many breaks in the series which no future researches will ever fill up.
Davidson on Fossil Brachiopoda.
It is from fossil conchology more than from any other department of the organic world that we may hope to derive traces of a transition from certain types to others, and fossil memorials of all the intermediate shades of form. We may especially hope to gain this information from the study of some of the lower groups, such as the Brachiopoda, which are persistent in type, so that the thread of our enquiry is less likely to be interrupted by breaks in the sequence of the fossiliferous rocks. The splendid monograph just concluded by Mr. Davidson, on the British Brachiopoda, illustrates, in the first place, the tendency of certain generic forms in this division of the mollusca to be persistent throughout the whole range of geological time yet known to us; for the four genera Rhynchonella, Crania, Discina, and Lingula have been traced through the Silurian, Devonian, Carboniferous, Permian, Jurassic, Cretaceous, Tertiary, and Recent periods,