HKB
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.
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. Babington the second, in their well-known treatises on British plants.