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, 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.
CHAPTER 22. — OBJECTIONS TO THE HYPOTHESIS OF TRANSMUTATION CONSIDERED.
Statement of Objections to the Hypothesis of Transmutation
founded on the Absence of Intermediate Forms.
Genera of which the Species are closely allied.
Occasional Discovery of the missing Links in a Fossil State.
Davidson's Monograph on the Brachiopoda.
Why the Gradational Forms, when found, are not accepted as
Evidence of Transmutation.
Gaps caused by Extinction of Races and Species.
Vast Tertiary Periods during which this Extinction has been going
on in the Fauna and Flora now existing.
Genealogical Bond between Miocene and Recent Plants and Insects.
Fossils of Oeningen.
Species of Insects in Britain and North America represented by
distinct Varieties.
Falconer's Monograph on living and fossil Elephants.
Fossil Species and Genera of the Horse Tribe in North and
South America.
Relation of the Pliocene Mammalia of North America, Asia,
and Europe.
Species of Mammalia, though less persistent than the Mollusca,
change slowly.
Arguments for and against Transmutation derived from the Absence
of Mammalia in Islands.
Imperfection of the Geological Record.
Intercalation of newly discovered Formation of intermediate Age
in the chronological Series.
Reference of the St. Cassian Beds to the Triassic Periods.
Discovery of new organic Types.
Feathered Archaeopteryx of the Oolite.
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 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.