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Show 212 THE DESCENT OF l\IAN. PART I. kingdom of the Vertebrata it has culminated in man. It must not, however, be supposed that groups of organic beings are always supplanted and disappear as soon as they have given birth to other and more perfect groups. The latter, though victorious over their predecessors, may not have become better adapted for all places in the economy of nature. Some old forms appear to have survived from inhabiting protected sites, where they have not been exposed to very severe competition; and these often aid us in constructing our genealogies, by giving us a fair idea of former and lost populations. But we must not fall into the error of looking at the existing members of any lowly-organised group as perfect representatives of their ancient predecessors. The most ancient progenitors in the kingdom of the Vertebrata, at which we are able to obtain an obscure glance, a pparen tl y consisted of a group of marine animals, 27 resembling the larvre of existing Aseidians. These animals probably gave rise to a group of fishes, as lowly organised as the lancelet; and from these the Ganoids, and other fishes like the Lepidosiren, must have been developed. From such fish a very small advance would 27 All vital functions tend to run their course in fixed and recurrent periods, and with tidal animals the periods would probably be lunar ; for such animals must have been left dry or covered deep with watersupplied with .copious food or stinted,-during endless generations: nt regular lunar mtervals. If then the Vertebrata are descended from an animal allied to the existing tidal Ascidians, the mysterious fact, that with the higher anu now t errestrial Vertebrata, not to mention other classes, many normal and abnormal vital processes run theit· comse ~cordin~ to lunar periods, is rendered intelligible, A recurrent period, 1f approximately of the right duration, when once gained, would not as far as we can judge, be liable to be changed; consequently it mi~ht be thus transmitted during almost any number of generations. This conclusion, if it could be proved sound, would be curious; for we should then see ~hat the period of gestation in each mammal, and the hatching of.each ?ud'~ eggs, and many other vital processes, still betrayed the prtmordtal buthplace of these animals. CIIAP. VI. AFFINITIES AND GENEALOGY. 213 carry us on to the amphibians. \V e have seen that birds and reptiles were once intimately connected together; and the Monotremata now, in a slight degree, connect mammals with reptiles. But no one can at present say by what line of descent the three higher and related classes, namely, mammals, birds, and reptiles, were derived from either of the two lower vertebrate classes, namely amphibians and fishes. In the class of mammals the steps are not difficult to conceive which led from the ancient Monotremata to the ancient Marsupials; and from these to the early progenitors of the placental mammals. We may thus ascend to the Lemuridre; and the interval is not wide from these to the Simiadre. The Simiadre then branched off into two great stems, the New World and Old World monkeys; and from the latter, at a remote period, Man, the wonuer and glory of the Universe, proceeded. Thus we have given to man a pedigree of prodigious length, but not, it may be said, of noble quality. The world, it. has often been remarked, appears as if it bad long been preparing for the advent of man; and this, in one sense is strictly true, for he owes his birth to a long line of progenitors. If any single link in this chain had never existed, man would not have been exactly what he now is. Unless we wilfully close our eyes, we may, with our present knowledge, approximately recognise our parentage ; nor need we feel ashamed of it. The most bumble organism is something much higher than the inorganic dust under our feet; and no one with an unbiassed mind can 8tudy any living creature, however bumble, without being struck with enthusiasm at its marvellous structure and properties. |