Most inferences must thus be extremely questionable. If a progressionistargues that the earliest known vertebrate remains are those of Fishes, whichare the most homogeneous of the Vertebrata; that Reptiles, which are moreheterogeneous, are later; and that later still, and more heterogeneous still,are Mammals and Birds; it may be replied that the Palaeozoic deposits, notbeing estuary deposits, are not likely to contain the remains of terrestrialVertebrata, which may nevertheless have existed. A like answer may be madeto the argument that the vertebrate fauna of the Palaeozoic period, consisting,so far as we know, entirely of Fishes, was less heterogeneous than the modernvertebrate fauna, which includes Reptiles, Birds and Mammals, of multitudinousgenera; while a uniformitarian may contend with great show of truth, thatthis appearance of higher and more varied forms in later geologic eras, wasdue to progressive immigration -- that a continent slowly upheaved from theocean at a point remote from pre-existing continents, would necessary bepeopled from them in a succession like that which our strata display. Atthe same time the counter-arguments may be proved equally inconclusive. When,to show that there cannot have been a continuous evolution of the more homogeneousorganic forms into the more heterogeneous ones, the uniformitarian pointsto the breaks which occur in the succession of these forms, there is thesufficient answer that current geological changes show us why such breaksmust occur, and why, by subsidences and elevations of large areas, theremust be produced breaks so immense as those which divide the great geologicepochs. Or again, if the opponent of the development hypothesis cites thefacts set forth by Professor Huxley in his lecture on "Persistent Types"-- if he points out that "of some two hundred known orders of plants,not one is exclusively fossil," while "among animals, there isnot a single totally extinct class; and of the orders, at the outside notmore than seven per cent are unrepresented in the existing creation"-- if he urges that among these some have continued from the Silurian epochto our own day with scarcely any change and if he infers that there is amuch greater average resemblance between the living forms of the past andthose of the present, than consists with the hypothesis; there is still asatisfactory reply, on which in fact Prof. Huxley insists; namely, that wehave evidence of a "pre-geologic era" of unknown duration. And,indeed, when we remember that the enormous subsidences of the Silurian periodshow the Earth's crust to have been approximately as thick then as it isnow -- when we conclude that the time taken to form so thick a crust, musthave been immense as compared with the time which has since elapsed -- whenwe assume, as we must, that during this comparatively immense time the geologicand biologic changes went on at their usual rates; it becomes manifest, notonly that the palaeontological records which we find do not negative thetheory of evolution, but that they are such as might rationally be lookedfor.
Moreover, though the evidence suffices neither for proof nor disproof,yet some of its most conspicuous facts support the belief, that the moreheterogeneous organisms and groups of organisms, have been evolved from theless heterogeneous ones. The average community of type between the fossilsof adjacent strata, and especially the community found between the latesttertiary fossils and creatures now existing, is one of these facts. The discoveryin some modern deposits of such forms as the Pataeotherium and Anaplotherium,which, according to Prof. Owen, had a type of structure intermediate betweensome of the types now existing, is another of these facts. And the comparativelyrecent appearance of Man, is a third fact of this kind, which possesses stillgreater significance.*<*I leave these sentences as they stood when writtennearly forty years ago, thinking it better to name in a note the vast amountof confirmatory evidence which has accumulated in the interval, and whichrenders unassailable the conclusion drawn. In 1862 no one thought it possiblethat there could be proof of a transition between reptiles and birds; andyet since that time forms unquestionably transitional have been found. Thoughthe indications of many other such kinships, by the discoveries of intercalaryforms, have not yet in most cases been followed by proofs of continuous genealogy,yet it is otherwise in the case of the horse, the ancestry of which has beentraced. Evidence of descent from a three-toed animal of the Miocene periodis considered by Prof. Huxley as conclusive: sceptical and cautious thoughhe is. In his Inaugural Address to the Geological Society in 1870, on "Paleontologyand the Doctrine of Evolution." many further illustrations are givenof kinships between ancient and modern types. Nowadays, indeed, there isuniversal agreement among naturalists (a few surviving disciples of Cuvierin France being excepted) that all organic forms have arisen by the superposingof modifications upon modifications: increase in heterogeneity being an averageimplication.>
