688 



theoiy. The explanation offered is the extreme 

 the almost incredible imperfection of the geological 

 record. Only a small portion of the globe has been 

 geologically explored with care ; only certain classes 

 of beings nave been fossilised ; and the number, 

 both of specimens and species yet discovered, is 

 absolutely as nothing compared with the number 

 which must have passed away during even a single 

 formation. The Malay Archipelago equals in area 

 the formations best known to us ; its present 

 condition represents that of Europe while Europe's 

 strata were being^ deposited ; its fauna and flora 

 are among the richest on the globe, yet, even if all 

 the species were to be collected which ever lived 

 there, how imperfectly would they represent the 

 natural history of the world ! Only few species are 



E reserved at all, and most of these in an imper- 

 jct manner ; moreover, subsidence being almost 

 necessary for the accumulation of rich deposits, 

 great intervals of time must have elapsed between 

 successive formations, so that during periods of ele- 

 vation, when variation would be most frequent, the 

 record is least perfect. Moreover, geological forma- 

 tions have not been continuously deposited ; the 

 duration of specific forms probably exceeds that of 

 each formation ; migrations have largely taken 

 place ; widely ranging species are most variable, 

 and oftenest give rise to new species ; varieties 

 have been at first local ; and finally, it is probable 

 that periods of modification are short as compared 

 with periods of permanence. Hence we cannot find 

 innumerable varieties, and any linking variety 

 between two forms is, of course, ranked as a distinct 

 species, for the whole chain cannot be permanently 

 restored. Thus the geological record is a history of 

 the world indeed, but one imperfectly kept, and 

 written in a changing dialect ; of this history we 

 possess the last volume only, relating to two or 

 three countries. Even of this volume only here and 

 there has a short chapter been preserved, and of 

 each page only here and there a few lines. 



Geological Succession of Organic Beings ( Distribu- 

 tion in Time}. The preceding difficulties excepted, 

 the facts of paleontology agree admirably with the 

 theory. New species come in slowly and succes- 

 sively ; they change in different rates and degrees ; 

 old forms pass through rarity to extinction, and 

 never reappear ; dominant forms spread and vary, 

 their descendants displacing the inferior groups, so 

 that after long intervals of time the productions of 

 the world appear to have changed simultaneously. 

 The most ancient forms differ most widely from 

 those now living, yet frequently present characters 

 intermediate between groups now widely divergent, 

 and they resemble to a remarkable extent the 

 embryos of the more recent and more highly 

 specialised animals belonging to the same classes. 

 These laws, and, above all, the important law of the 

 succession of the same types within the same areas 

 during the later geological periods, and most 

 notably between the Tertiary period and the 

 present time (e.g. fossil and recent marsupials in 

 Australia, and edentates in South America), cease 

 to be mysterious, and become at once thoroughly 

 intelligible on the principle of inheritance, and on 

 that alone. 



[ Since the publication of the Origin of Species in 

 1859, palaeontological research has been constantly 

 furnishing the most triumphant verification of these 

 views. The imperfection of the geological record 

 was so far from overestimated that Huxley 

 (Science and Culture, 1880), in comparing our 

 present knowledge of the mammalian Tertiary 

 fauna with that of 1859, states that the results of 

 the investigations of Gaudry, Marsh, and Filhol 

 are ' as if zoologists were to become acquainted with 

 a country hitherto unknown, as rich in novel forms 

 of life as Brazil or South Africa once were to 



Europeans.' Gaudry has found the intermediate 

 stages by which civets passed into hyrenas ; Filhol 

 has disinterred still more remote ancestral carni- 

 vores ; while Marsh has obtained a complete series of 

 forms intermediate between that, in some respects, 

 most anomalous of mammals, the horse, and the sim- 

 plest five-toed ungulates (see MAMMALS). Again, 

 Darwin's belief that the distinctness of birds from 

 all other vertebrates was to be accounted for by the 

 extinction of a long line of progenitors connecting 

 them with reptiles, was in 1859 a mere assumption ; 

 but in 1862 the long-tailed and intensely reptilian 

 bird Archoeopteryx (q.v. ) was discovered, while in 

 1875 the researches of Marsh brought to light 

 certain cretaceous birds, one (Hesperornis) with 

 teeth set in a groove, the other ( Ichthyornis ) with 

 teeth in sockets, and with bi-concave vertebrae. 

 Besides these reptilian birds, bird-like reptiles have 

 similarly been forthcoming, and the hypothesis of 

 Darwin is thus admirably verified. Considerable 

 light, too, has been thrown on the pedigree of 

 crocodiles ; ammonites, trilobites, ana other in- 

 vertebrates have been arranged in series, while 

 important collateral evidence is also furnished by 

 'persistent types' such as Ceratodus, Beryx, 

 Nautilus, Lingula, &c., which have survived we 

 must assume by ordinary generation almost com- 

 pletely unchanged since remote geological periods. 

 On such grounds, therefore, Huxley asserts (op. cit.) 

 that 'on the evidence of palaeontology, the evolu- 

 tion of many existing forms of animal life from 

 their predecessors is no longer an hypothesis, but 

 an historical fact ; it is only the nature of the 

 physiological factors which is still open to dis- 

 cussion. ' ] 



Geographical Distribution. Neither the simi- 

 larity nor the dissimilarity of the inhabitants of 

 various regions, whether of land or sea, can be 

 accounted for by identity or differences of climate, 

 or other physical conditions, but both are related in 

 the most striking degree to the absence or presence 

 of barriers to migration between those regions. 

 Within the same area there exists the most marked 

 affinity among the species, though these differ from 

 place to place. Species appear to have arisen in 

 separate definite centres, the few apparent excep- 

 tions being accounted for by migration and dis- 

 persal, followed by climatic and geographical 

 changes. But for a summary of our knowledge of 

 the existing mode of distribution of organic life, 

 and of the way in which that distribution has been 

 effected, as well as of the very important bearing of 

 these facts upon the theory of evolution, which 

 they may be said, indeed, more than any other 

 class of facts, to have suggested, see the article 

 GEOGRAPHICAL DISTRIBUTION. 



Morphological Arguments. The physiological 

 and distributional lines of argument being sum- 

 marised, those furnished by morphology, although 

 not less numerous and highly important, can only be 

 very briefly outlined. These are mainly four, and 

 are derived from (a) Classification, (b) Homologies, 

 (c) Embryology, (d) Rudimentary Organs. 



(a) Classification. Naturalists arrange the 

 species, genera, and families in each class, on what 

 is called the Natural System. But what is meant 

 by this system ? Is it, after all, merely an artificial 

 scheme for enunciating general propositions, and of 

 placing together the forms most like each other ? 

 or does it, as many believe, reveal the plan of crea- 

 tion ? The grand fact of classification is, that 

 organic beings, throughout all time, are arranged 

 in groups subordinated under other groups in- 

 dividuals under varieties, and these again under 

 species ; species under genera ; genera under sub- 

 families, families, and orders ; and all under a few 

 grand classes. The nature of all these relation- 

 ships the rules followed and the difficulties met 



