On the Genesis of Species

auria, Chelonia, and Anoura.-Horse ancestry.-Labyrinthodonts and Trilobites.-Two subdivisions of the second relation of species to time.-Sir William Thomson's views.--Probable period re

nian evolution.-High organization of Silurian forms of life

the necessary relation of species to time if the th

ces of the past existence of intermedi

for the evolution of all organic forms from a few original on

ural Selection" alone, because not only are minutely transitional forms generally absent, but

ue, it would be more probable that no two specimens preserved as fossils should be of one variety than that we should find a great many specimens collected from a very few varieties, provided, of course, the chances of preservation are equal for all individuals." "It is really st

rtain series of minutely intermediate fossil specimens. The mass of pal?ontological evidence is indeed overwhelmingly against minute and gradual modification. It is true that when once an animal has obtained powers of flight its means of diffusion are indefinitely increased, and we might expect to find many relics of an a?rial form and few of its antecedent state-with nascent wings just commen

PTERODACTYLE,

the exact type of existing forms, and there is as yet no indica

pterodactyles, though surely some of the many incipient forms, which on th

ons for thinking that the line of affinity between birds and reptiles passes to the birds last named from the Dinosauria rather than from the Pterodactyles, through Archeopteryx-like forms to the ordinary birds. Finally, he has thrown out the suggestion that the celebrated footsteps left by some extinct three-toed creatures on the very ancient sandstone of Connecticut were made, not, as hitherto supposed, by true birds, but by more or less ornithic reptiles. But even supposing all that is asserted or inferred on this subj

) existed at a time, when, as yet, we have no evidence of some of the Dinosauria having come into being. Moreover, if the remarkable and minute similarity of the coracoid of a pterodactyle to that of a bird be merely the result of function and

RYX (OF THE O

OF AN ICH

be. Yet no single transitional form has yet been met with in spite of the multitudinous individuals preserved. Again, with their modern representatives the Cetacea, one or two aberrant forms alone have been found, but no series of transitional ones indicating minutely the line of descent. This group, the

OF A PLES

eme form without any, as yet known, transitional stages. Another group may be finally mentioned, viz. the frogs and toads, anourous Bat

indefinite fortuitous variations. On the contrary, the series is an admirable example of successive modification in one special direction along one beneficial line, and the teleologist must here be allowed to consider that one motive of this modification (among probably an indefinite number of motives inconceivable to us) was the relationship in wh

ause the foot of Hipparion, e.g., and a fortiori the broader based three-hoofed foot of the Pal?othere, to sink less deeply into swampy soil, and be more easily withdrawn than the more concentratively simplified and specialized foot of the horse. Rhinoceroses and zebras, however, tread together the arid plains of Africa

hich up till then had been discovered, seemed to justify the opinion that as time went on, forms had successively appeared with more and more complete segmentation and ossification of the backbone, which in the earliest forms was (as it is in the lowest fishes now) a soft continuous rod or notochord. Now, however, it is considered probable that the soft back-boned Labyrinthodont Archegosa

LOB

the Darwinian theory, provided a sufficiently enormous amount of past time be allowed. The alleged extreme, and probably great, imperfection of that record may indeed be pleaded in excuse. But it is an excuse.[132] Nor is it

y other sciences for organic evolution; and (2) the proportion existing, on Darwinian principles, between the time anterior to the earlier fossils, and the

of the earth. The result arrived at by these investigations is a conclusion that the existing state of things on the earth, life on the earth, all geological history showing continuity of life, must be limited within some such period of past time as one hundred million years. The first question which suggests itself, supposing Sir W. T

favour when we consider how much they tell against the theory of Mr. Darwin. The last-named author only remarks that "many of the elements in the calculation are more or less doubtful,"[134

, puts the probable date of the beginning of the Cambrian deposits[137] at only twenty-four million years ago. On the other hand, he seems to c

of all organic forms by merely accidental, minute, and fortui

think that geological time is too short for the evolution of the higher forms of life out of the lower

d by long-continued selection under domestication; and there is no reason to suppose that any of the variations which have been selected to form it have been other than gradual and almost imperceptible. Suppose that it has taken five hundred years to form the greyhound

ion of the most useful or beautiful animals, with no intention of modifying the breed." He adds: "But by this pro

e time. This slowness follows from all the inhabitants of the same country being already so well adapted to each other, that places in the polity of nature do not occur until after long intervals, when changes of some kind in the physical conditions, or through immigration, have occurred, and individual differences and variations of the right nature, by which some of the inhabitants might be better fitted to their new places under altered cir

and years be taken to represent approximately the period of substantially constant conditions during which no considerable change would be brought about. Now, if one thousand years may represent the period required for the evolution of the species S. nasalis, and of the other species of the genus Semnopithecus; ten times that period shoul

mals; for those between primary placental and implacental mammals, and perhaps also for the divergence of the most ancient stock of these and of the monotremes, for in all these cases modifications of structure appear to increase in complexity in at least that ratio. Finally, a vast period must be granted for the development of the lowest mammalian type from the primitive stock of the whole vertebrate sub-kingdom. Supposing this primitive stock to have arisen directly from a very l

e deposition of the strata which must have been deposited, if all

. Darwin's theory be true, past time down to the deposition of the Upper Silurian strata can have been but a very small fraction of that during which strata have been deposited. F

ps which are known to have ever been developed, namely, the Elasmobranchs (the highly organized sharks and rays) and the Ganoids, a group now poorly represented, but for which the sturgeon may stand as a type, and which in many important respects more nearly resemble higher Vertebrata than do th

s, or cuttle-fish class; and amongst articulated animals we find Trilobites and Eurypterida, which do

LE-F

spect. B. Do

t only once, for in the fishes and mollusca we have (as described in the third chapter of this work) the coincidence of the independently developed organs of sense attaining a nearly similar complexity in two quite distinct forms. If, then, so small an advance has been made in fishes, molluscs, and art

g this deposition, only represents a hundredth part of the sum total, we shall require 2,500,000,000 (two thousand five hundred million) years for the complete development of the wh

was then as abundant and varied as, on the Darwinian theory, it must have been. Mr. Darwin himself admits[141] "the case

trilobites, which seemed to exhibit gradual change, are shown by further investigation to do nothing of the sort. As regards the time required for evolution (whether estimated by the probably minimum period required for organic change or for the deposition of strata which accompanied that change), reasons have been suggested why it is likely that the past history of the earth does not supply us with enough. First, because of the prodigious increase in th

lved according to laws in part depending on surrounding conditions, in part internal-similar to the way in which crystals (and, perhaps from recent researches, the lowest fo