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?