Page images
PDF
EPUB

of its kind). These varieties, in the struggle for existence, have unequal fortune; those individuals in which the variations are of a favourable character, will be more vigorous; those most adapted to the circumstances of the time and place prosper, and give origin to descendants, which run the same risks, but which, under the principle of what Mr. Darwin calls “Natural Selection,” acquire more and more the character of distinctness and superiority. In this struggle the weakest, in common phrase, goes to the wall, and there is what Herbert Spencer calls 6. The survival of the fittest." The theory of Natural Selection is the doctrine of Malthus applied to the animal and vegetable world; a struggle for existence inevitably follows, owing to the tendency to geometrical increase of all kinds of animals and plants; and as more individuals are produced than can possibly survive, those individuals having any advantage, however slight over others, will have the best chance of surviving and of procreating their kind, while, on the other hand, any variation in the least degree injurious will be rigidly destroyed.

Mr. Darwin maintains the doctrine that species are not immutable. “Although much remains obscure,” says he, “and will long remain obscure, I can entertain no doubt, after the most deliberate study and most dispassionate judgment of which I am capable, that the view which most naturalists entertain, and which I formerly entertained, namely, that each species has been independently created, is erroneous. I am fully convinced that species are not immutable, but that those belonging to what are called the same genera are lineal descendants of some other and generally extinct species, in the same way as the acknowledged varieties of any one species are the descendants of that species.”

In answer to the questions, “How is it that varieties which he calls incipient species become ultimately converted into good and distinct species, which in most cases obviously differ from each other far more than do the varieties of the same species ?”—“How do those groups of species which constitute what are called distinct genera, and which differ from each other more than do the species of the same genus, arise ?” he says, “ All these results follow from the struggle for life. Owing to this struggle, variations, however slight, and from whatever cause proceeding, if they be in any degree profitable to the individuals of a species, in their infinitely complex relations to other organic beings and to their physical conditions of life, will tend to the preservation of such individuals, and will generally be inherited by the offspring. The offspring, also, will thus have a better chance of surviving ; for of the many individuals of any species which are periodically born but a small number can survive. I have called this principle, by which each slight variation, if useful, is preserved, by the term Natural Selection, in order to mark its relation to man's power of selection. But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient. We have seen that man by selection can certainly produce great results, and can adapt organic beings to his own uses, through the accumulation of slight but useful variations given to

him by the hand of Nature. But Natural Selection is a power incessantly ready for action, and is immeasurably superior to man's feeble efforts, as the works of Nature are to those of Art.”

Breaking down the barrier of species, Mr. Darwin has endeavoured to deduce all the varieties of life that now are on the earth ; not only those of insects, birds, fishes, beasts, but those also of man, from a few forms of life, or from one primordial germ.

In accounting for these great changes, Mr. Darwin falls back upon "unlimited periods of time.” Now time is recognised in other physical sciences as an essential element of natural operations; but Mr. Darwin does not leave us even a guess in respect to how long a period it takes to modify a species, as he cannot point to any modification during the last several thousand years. He confesses, also, that many animals have remained unchanged since the commencement of the glacial period, “and these have been exposed to great changes of climate, and have migrated over great distances."

If the theory of Natural Selection is true, Geology ought to furnish the most valuable and complete evidence, in its support. But Mr. Darwin acknowledges that some of the facts of Geology are nearly fatal to his theory; and in order to surmount these difficulties, he lays great stress on the imperfection of the geological record. In the lowest known fossiliferous rocks “are found species belonging to several of the main divisions of the animal kingdom;" and Mr. Darwin says, that if his theory is true, "it is indisputable that before the lowest Cambrian stratum was deposited, long periods elapsed, as long as, or probably far longer than the whole interval from the Cambrian age to the present day, and that during these vast periods the world swarmed with living creatures."

Now Geology at present gives us no evidence of these vast periods, and Mr. Darwin acknowledges the almost entire absence as at present known of formations rich in fossils beneath the Cambrian stratum.

The next order of fossiliferous rocks is the Silurian. These rocks abound with oceanic life, which has been well · preserved, but there are no fish. Next in geological succession is the Devonian, when suddenly appear fish of the highest and most perfect type. “In short,” says Sir R. Murchison, “the first created fish, like the first forms of those other orders, was just as marvellously constructed as the last which made its appearance, or is now living, in our seas." Between those two great classes of the Mollusca and the fishes, there is no trace of any transitional forms, although the minutest organisms have been preserved. But, if life had been gradually developed from one or more primordial forms, surely the geologist ought to be able to arrange the fossil remains in a real though broken series, so as to form a few · links in this long chain of easy graduated life, however imperfect might be the geological record.

The continued operation of natural laws in the production of all organisms have always been noticed by naturalists and others, but Mr. Darwin was the first to give the term Selection exclusively to the action of those causes which are for ever shaping and modifying all animated and organic existences; and many centuries ago, even as far back as the time of Aristotle, the argument of “The

even

survival of the fittest” was discussed and reasoned out by those wise men of old.

Natural Selection, as put forth by Mr. Darwin, is a Providence without a God. He speaks of it as not only altering, but he attributes to it a creative power, involving the addition of new bones or new organs. Now, supposing Mr. Darwin's theory can account for the difference in the structure of an animal—the lengthening of the giraffe's neck, for instance, which may have been acquired by the original animal having been impelled by a succession of dearths to seek its food in the branches of trees, and thus to have extended its neck by constant use-can it,

within the infinite time required, by any outward conditions account for the various organs with which the higher animals are endowed ? How can it account, for instance, by numerous successive slight modifications for all the complex mechanism of the eye and

“Did light,” says Dr. Stirling, “or did the pulsations of the air, even by any length of time, indent into the sensitive cell, eyes and a pair of eyes—ears and a pair of ears ? Light, conceivably, might shine for ever without such a wonderfully complicated result as an eye. Similarly, for delicacy and marvellous ingenuity of structure, the ear is scarcely inferior to the eye; and surely it is possible to, think of a whole infinitude of those fitful and fortuitous air tremblings, which we call sound, without indentation into anything whatever of such an organ."

According to Lucretius, The eyes were not made to see with, but being formed by a 'fortuitous concurrence of atoms,' men, finding them well adapted for the purpose of seeing, used them as such. For, says he, if eyes

ear.

« PreviousContinue »