‘Are God and Nature then at strife,That Nature lends such evil dreams?So careful of the type she seems,So careless of the single life;‘“So careful of the type”? but no,From scarped cliff and quarried stoneShe cries, “A thousand types are gone:I care for nothing, all shall go.”’—Tennyson.
‘Are God and Nature then at strife,That Nature lends such evil dreams?So careful of the type she seems,So careless of the single life;‘“So careful of the type”? but no,From scarped cliff and quarried stoneShe cries, “A thousand types are gone:I care for nothing, all shall go.”’—Tennyson.
‘Are God and Nature then at strife,
That Nature lends such evil dreams?
So careful of the type she seems,
So careless of the single life;
‘“So careful of the type”? but no,From scarped cliff and quarried stoneShe cries, “A thousand types are gone:I care for nothing, all shall go.”’—Tennyson.
‘“So careful of the type”? but no,
From scarped cliff and quarried stone
She cries, “A thousand types are gone:
I care for nothing, all shall go.”’—Tennyson.
‘All nature is but art, unknown to thee;All chance, direction, which thou canst not see,All discord, harmony not understood;All partial evil, universal good;And spite of pride, in erring reason’s spite,One truth is clear, whatever is, is right.’—Pope.
‘All nature is but art, unknown to thee;All chance, direction, which thou canst not see,All discord, harmony not understood;All partial evil, universal good;And spite of pride, in erring reason’s spite,One truth is clear, whatever is, is right.’—Pope.
‘All nature is but art, unknown to thee;
All chance, direction, which thou canst not see,
All discord, harmony not understood;
All partial evil, universal good;
And spite of pride, in erring reason’s spite,
One truth is clear, whatever is, is right.’—Pope.
154. In the two preceding Chapters we have dwelt upon the laws of energy and the ultimate constitution of matter; in other words, we have discussed the laws according to which the machine called the visible universe works, as well as the probable nature of the material of which it is composed. We have in this process (Arts. 86, 151) come to the conclusion that the visible universe has been developed out of theinvisible. Once developed, it has its own laws of action which we may discover,—laws which at present appear to be invariably followed, as far at least as our strictly scientific experience can inform us.
In fine, the visible universe is that which we are in a position to observe; gaining an insight into its present method of working, and trying also to reply to the very interesting question, Has it always worked in its present manner, or has there ever been any apparent break?
Let us therefore consider this visible universe immediately after its production, and endeavour to become acquainted with the course of its development. What did it do? Was it, or was it not, entirely left to itself, and to what may be termed the natural laws impressed upon it when it was produced? Or, if the results of our inquiry seem to show that it was not entirely left to itself, when, to what extent, and for what purposes, has there been and is there interference proceeding from the unseen?
In replying to these questions, let us, for the sake of convenience, consider development under the three following heads, viz., (α) Chemical or Stuff Development, (β) Globe Development, (γ) Life Development.
155. Beginning with chemical or stuff development, we come at once to a very interesting and important question. Assuming that the atoms of the present universe were developed from the invisible, were different kinds of atoms thus developed, or were they all of one kind?
To this question the chemist of last century would have replied, that undoubtedly there were many kinds of primeval atoms, and then would follow a formidablelist of all these various substances which he was unable to decompose.
The chemist of thirty or forty years later would still have replied to the question in the same way, but he would probably have furnished a different list of primeval elements less formidable in number.
If the chemist of forty years ago had been asked, he would have furnished a list of perhaps fifty simple substances; but then, probably, the minimum would have been reached; for ask the chemist of to-day, and he will furnish a list of sixty-four so-called elements.
156. But while the number of as yet undecomposed bodies is slowly increasing by fresh discoveries, chemists are beginning to speculate as to the possibility that these so-called elements may be in reality nothing more than combinations differing in numbers and in tactical arrangement, of some one kind of primordial atoms.
This idea was first entertained by Dr. Prout, the well-known physician and chemist. He pointed out that the atomic weights of the various so-called elements are very nearly all multiples of the half of that of hydrogen, so that the various elements may possibly be looked upon as formed by a grouping together of certain atoms of half the mass of the hydrogen atom.
M. Stas, the distinguished Belgian chemist, instituted a laborious series of experiments with the view of testing this doctrine. He came to the conclusion that the atomic weights of the various elements were not precisely multiples of the half of that of hydrogen, there being greater differences than could possibly be accounted for by errors of experiment. Hisresearches, however, seemed to show that in many cases there was a very near approach to Prout’s imagined law. But in no case does the discrepance appear to us greatly to exceed what may easily be attributed to unavoidable impurities in the substances operated on; say only those due to the condensation of gases in the pores of solids, which (in certain cases at least) is known to amount to a very considerable quantity.
157. From another point of view there appears to be evidence in favour of the so-called elementary bodies being built up, as more or less complex arrangements of one, or at most a few, simpler kinds of matter.
There are certain groups or families amongst these elements of such a nature that the various members of one family appear to be related to each other, in the same way as the corresponding members of another family.
This clearly points to some sort of community of origin, and thus favours the idea that the elements are in reality composite structures. But the great difficulty felt by those who have favoured this idea has been the apparent impossibility of decomposing such family groups. Thus fluorine, chlorine, bromine, and iodine, while they appear to be related to one another in some peculiar manner, have yet apparently resisted all attempts at decomposition, and there are other similar instances which might easily be named.
158. It has, however, at the same time, come to be recognised, that heat of high temperature is a very powerful decomposing agent, and that its office is byno means limited to causing the separation from one another of the molecules of a substance, as, for instance, when it separates the molecules of water-substance or H2O from one another, as in forming water from ice, or steam from water. It is now understood that high-temperature heat has also the power of separating the atomic constituents of a single molecule from each other, so that at an extremely high temperature not only would water be driven into steam, but steam driven into oxygen and hydrogen. We are already familiar with many instances of this power possessed by high-temperature heat; thus we see carbonate of lime decomposed by the heat of the kiln into lime and carbonic-acid gas. We see also that at the high temperatures which accompany the electric spark almost all compounds are momentarily decomposed, if we may judge by the spectrum of the light which is given out. Carrying on this line of thought, we are led to imagine that, could we obtain higher temperatures than those now at our disposal, we might decompose some of those substances which at present seem to be elements.
159. Lockyer, in his astronomical researches, has recently started this question. He argues that in the sun and stars, and more especially in the whiter stars, there are temperatures very much higher than any which have been here produced. He assumes too that simplicity of constitution accompanies a simple spectrum, an hypothesis which is consistent with the fact that compounds as a rule give spectra much more complicated than those of simple substances. Now it is a curious circumstance that the atmospheresof some of the whiter stars, such as Sirius, do not appear to contain anything but hydrogen; at least we have no indication that they do; other stars, again, of less whiteness, in addition to hydrogen, have such substances as iron, sodium, etc., while yellow, orange, and blood-red stars and variable stars, appear to contain in their atmospheres substances which are compounds. If then it be true that as a rule the atmospheres of the whiter stars contain the fewer elements and those of smallest atomic weight, and that as stars diminish in whiteness their atmospheres rise in complexity of structure, in fine, if we have reason to associate together whiteness and simplicity, this undoubtedly tells in favour of the power of high-temperature heat to split up the so-called elements.
We conclude the whiter stars to be the hotter stars, from the fact that their spectra contain a greater proportion of the more refrangible rays than do those of yellow or red stars.
In fine, a speculation of this nature is not to be summarily dismissed, but ought to be retained as a working hypothesis which may in time throw great light on the ultimate constitution of the chemical elements. Is it fanciful to suppose that the passage prefixed toChapter III. may refer to this, since (literally translated) it stands—‘... the elements, intensely heated, shall be broken up....’?
160. Let us now turn to globe development. We have alluded to this already while discussing the energy of the universe. In doing so we came to the conclusion that the original state of the visible universe was a diffused or chaotic state, in which the various particles were widely separated from oneanother, but exerting on one another gravitating force, and therefore possessed of potential energy. As these particles came together, impinged on one another, or gathered into groups, this potential energy was gradually transformed into the energy of heat and into that of visible motion. We may thus imagine the cooling and (except under very strict conditions of original distribution)necessarilyrevolving matter in course of time to have thrown off certain parts of itself which would thereafter form satellites or planetary attendants, while the central mass would form the sun. We have here, in fact, the development hypothesis of Kant and Laplace, and it is greatly in favour of the truth of this hypothesis that all the planetary motions of the solar system are nearly in one plane, and also that, looking down on the system from above that plane, all these motions are seen to be in one and the same direction.
161. Assuming, therefore, that the solar system and,pari passu, the other sidereal systems have been formed in this way, it is very easy to see why the central mass should be so much hotter than its attendants. Two causes would conduce to this. In the first place, assuming that the heat of a mass is due to the rushing together of its particles under the force of gravitation, the velocities would be much greater for the central mass, and hence the amount of heat (per unit of mass,i.e.the temperature) developed would be greater also. In the next place, the body being a large one would cool less rapidly than its attendant planets. These two causes thus combine to render the largest bodies of the universe ever since their aggregation (and still more now) thehottest, so that the same body which forms the gravitating centre of the system becomes, when required, also the dispenser of light and heat.
162. Now, without speculating about the nature or extent of the ethereal medium, we may be sure of two things. In the first place, all but an exceedingly small fraction of the light and heat of the sun and stars goes out into space and does not return to them again, or in other words, the sun and stars are slowly cooling. To restore to the sun every instant its losses by radiation, the whole celestial vault would have to radiate as powerfully as the sun does—in which case the earth and planets would very soon acquire (at their surfaces) the sun’s temperature. In the next place, the visible motion of the large bodies of the universe is gradually being stopped by something which may be denominated ethereal friction. It follows from this that our own sun will gradually lose his brilliancy, and that our earth will gradually lose its orbital energy and approach the sun in a path of slowly contracting spiral convolutions. At last it will become entangled with the sun, and the result will be the conversion of the remaining orbital energy into heat, after which the two bodies will remain one.
Thus the tendency is that the sun shall ultimately absorb the various planets of the system, his heat and energy being recruited by the process. Now, let us imagine that the same processes are simultaneously going on in one of the nearer fixed stars, say for instance in Sirius.
After unimaginable ages these two stars, the Sun and Sirius, having each long since swallowed up his attendants, but being nevertheless exhausted in heat-energy on account of radiation into space, may beimagined to be travelling towards one another, slowly at first, but afterwards with an accelerated motion.
They will at last approach each other with a great velocity, and finally form one system. Ultimately the two will rush together and form one mass, the orbital energy of each (or rather that portion of this energy which remains after ethereal friction) being converted into heat, and the matter being, in consequence, probably partly smashed into mere dust, and partly evaporated and transformed into a gaseous, nebulous condition. Ages pass away, and the large double mass ultimately shares the same fate that long since overtook the single masses which composed it; that is to say, it shrinks and throws off planets, but gives out the greater part of its light and heat into space and gradually becomes cold and dark, until at length it comes to form one of the constituents of a still more stupendous collision, and has its temperature raised once again by the conversion of visible energy into heat.
163. Our readers will remark how, by a process of this kind, the primordial potential energy of the visible universe is gradually converted into light and heat, and how this light and heat are ultimately dissipated into space. They will also remark that, as the process goes on, the masses of the universe become larger and larger. In fine, the dissipation of the energy of the visible universe proceeds,pari passu, with the aggregation of mass.
The very fact, therefore, that the large masses of the visible universe are of finite size, is sufficient to assure us that the process cannot have been going on for ever; or, in other words, that the visible universe must have had its origin in time, and we may conclude that if the visible universe be finite in mass theprocess will ultimately come to an end. All this is what would take place, provided we allow the indestructibility of ordinary matter; but we may perhaps suppose (Art. 153) that the very material of the visible universe will ultimately vanish into the invisible.
164. There is one peculiarity of the process of development just described, which we beg our readers to note. We have supposed the visible universe, after its production, to have been left to its own laws; that is to say, to certain so-called inorganic agencies, which for want of better knowledge we for the present call forces, in virtue of which its development took place.[51]At the very first there may have been only one kind of primordial atom, or, to use another expression, absolute simplicity of material. As, however, the various atoms approached each other, in virtue of the forces with which they were endowed, other and more complicated structures took the place of the perfectly simple primordial stuff. Various kinds of molecules were produced at various temperatures, and these ultimately came together to produce globes or worlds, some of them comparatively small, others very large. Thus the progress is from the regular to the irregular. And we find a similar progress when we consider the inorganic development of our own world. The action of water rounds pebbles, but it rounds them irregularly; it produces soil, but the soil is irregular in the size of its grains, and variable in constitution. Wherever what may be termed the brute forces of nature are left to themselves, this is always the result: not so,however, when organisms are concerned in the development. Two living things of the same family are more like each other than two grains of sand or than two particles of soil. The eggs of birds of the same family, the corresponding feathers of similar birds, the ants from the same ant-hill, all form groups whose members have a very strong likeness to each other.
We find this likeness still more marked when we regard certain products of human industry. Let us take, for instance, coins from the same die, or bullets from the same mould, or impressions from the same engraved plate, and we at once perceive the striking difference between products developed through inorganic means and those developed through an intelligent agent designing uniformity.
165. Let us now proceed to consider life development. Let us imagine that the primeval atoms have long since come together, various chemical substances being the result. And let us further imagine that these various substances have long since gathered themselves into worlds, of various sizes at first; but that these worlds have gradually cooled down, until one of them, the Earth, let us say, has at length reached conditions under which life (such as we know it) becomes possible. Accordingly life makes its appearance; not the life that now is, but something much ruder and simpler. But in process of time we find quite a different order of organised beings; a higher and more complete type has appeared, and the type continues to rise until it culminates in the production of man, a being endowed with intelligence, and capable of reasoning upon the phenomena around him. Now, if man reviews these organised formswhich exist on the earth side by side with himself, he perceives at once that a number of individuals possess certain characteristics in common, and he gives expression to this experience by saying that these individuals are all of one species. ‘When we call a group of animals or of plants a species,’ says Professor Huxley,[52]‘we may imply thereby, either that all these animals or plants have some common peculiarity of form or structure; or we may mean that they possess some common functional character. That part of biological science which deals with form and structure is called Morphology; that which concerns itself with function, Physiology. So that we may conveniently speak of these two senses, or aspects, of “species”—the one as morphological, the other as physiological.... Thus horses form a species, because the group of animals to which that name is applied is distinguished from all others in the world by the following constantly associated characters:—They have, 1. a vertebral column; 2. mammae; 3. a placental embryo; 4. four legs; 5. a single well-developed toe in each foot, provided with a hoof; 6. a bushy tail; and 7. callosities on the inner sides of both the fore and the hind legs. The asses, again, form a distinct species, because, with the same characters, as far as the fifth in the above list, all asses have tufted tails, and have callosities only on the inner side of the fore legs.’
But very often the morphological peculiarities of a species are more easily recognised than expressed. No one, for instance, would fail to rank the horse as one species and the ass as another, even while ignorant of some of those specific peculiarities which the naturalistselects as conveying the best scientific account of their difference.
166. Let us now regard the question of species from its physiological point of view. Suppose that two individuals, A and B, of different sexes, breed freely together, producing offspring, and that two individuals, C and D, do the like.
Now, if the offspring of A and B is capable of breeding freely with that of C and D, producing offspring, generation after generation, then A, B, C, and D may be said to belong to the same physiological species.
To take an illustration borrowed from Professor Huxley: let us imagine that A is an Arab, and B a dray-horse; also that C is a dray-horse, and D an Arab. Now the progeny of these two pairs will all be mongrels, holding a position intermediate between that of the Arab and the dray-horse; but they will be perfectly fertile amongst themselves when matched together. We therefore conclude that the dray-horse and the Arab are not distinct physiological species, but only varieties of the same species. Again, let A be a horse and B an ass, also let C be an ass and D a horse. The pairs will still have offspring, and these will be mules, having a character intermediate between that of the horse and that of the ass; but, on the other hand, these mules will not be able to breed together amongst themselves so as to produce offspring. We are therefore justified in asserting that a horse and an ass are of different physiological species.
If we should ever attempt to pair together animals much more unlike each other than the horse and theass, we should simply fail. They will not come together, and we cannot tell whether, if they did, they would be capable of producing progeny. We may therefore conclude that, as matter of fact, there are certain well-marked physiological species that will not breed with each other at all, while there are other species also physiologically distinct, but not so markedly separated from each other, that may be brought to breed together, their offspring being infertile.
167. The most apparent conclusion to be deduced from these facts would be that of the invariability of species, and of the impossibility of its transmutation—the infertility of hybrids being the law which prevents any such transmutation from taking place. And as the physiological species cannot be made different the apparent conclusion is that in times past they have been always the same as they are now. If this be allowed, it follows that inasmuch as they took their origin in time, they must have originally been produced very much as they are at the present moment,—a separate act of production being required for each species, or rather two separate acts for each species. This position has always been regarded as a stronghold by a certain class of theological thinkers, and they have resented the attempts of men of science to obtain any other explanation of the origin of species.
Men of science have, on the other hand, asserted their right to discuss this question with the same freedom as any other. Our point of view is somewhat different from that of either of these two parties. We think it is not so much the right or privilege as the bounden duty of the man of science to put back thedirect interference of the Great First Cause—the unconditioned—as far as he possibly can in time. This is the intellectual or rather theoretical work which he is called upon to do—the post that has been assigned to him in the economy of the universe.
If, then, two possible theories of the production of any phenomenon are presented to the man of science, one of these implying the immediate operation of the unconditioned, and the other the operation of some cause existing in the universe, we conceive that he is called upon by the most profound obligations of his nature and work to choose the second in preference to the first. But we have already sufficiently discussed this question in a previous part of this book (Art. 85).
168. When we examine closely into the phenomena of life we find that side by side with the general law, that like produces like, there is a tendency to minor variations.
Thus we have already agreed to consider dray-horses and Arabs as varieties of the species horse; and in like manner pouters, carriers, fan-tails, and tumblers are all varieties of the species rock-pigeon. We are therefore led to ask how such varieties were originally produced, and how they become perpetuated after their production.
Now it is well known that there occurs occasionally an accountable variation, so marked in its nature as to be worthy of historical record. Two very interesting and instructive instances of this are given by Professor Huxley, and we take the liberty of quoting these in the Professor’s ownwords:—
‘The first of them is that of the “Ancon,” or “Otter” sheep, of which a careful account is given by Colonel David Humphreys, F.R.S., in a letter to Sir Joseph Banks, published in thePhilosophical Transactionsfor 1813. It appears that one Seth Wright, the proprietor of a farm on the banks of the Charles River in Massachusetts, possessed a flock of fifteen ewes and a ram of the ordinary kind. In the year 1791, one of the ewes presented her owner with a male lamb differing, for no assignable reason, from its parents by a proportionally long body and short bandy legs, whence it was unable to emulate its relatives in those sportive leaps over the neighbours’ fences, in which they were in the habit of indulging, much to the good farmer’s vexation.‘With the ’cuteness characteristic of their nation, the neighbours of the Massachusetts farmer imagined it would be an excellent thing if all his sheep were imbued with the stay-at-home tendencies enforced by nature upon the newly arrived ram, and they advised Wright to kill the old patriarch of his fold, and install the Ancon ram in his place. The result justified their sagacious anticipations.... The young lambs were almost always either pure Ancons or pure ordinary sheep. But when sufficient Ancon sheep were obtained to interbreed with one another it was found that the offspring was always pure Ancon.’‘The second case is that detailed by a no less unexceptionable authority than Réaumur, in hisArt de faire éclore les Poulets. A Maltese couple named Kelleia, whose hands and feet were constructed upon the ordinary human model, had born to them a son, Gratio, who possessed six perfectly moveable fingers on each hand, and six toes, not quite so well formed, on each foot. No cause could be assigned for the appearance of this unusual variety of the human species. But however they may have arisen, what especially interests us is to remark that, once in existence, varieties obey the fundamental law of reproduction, that like tends to produce like, and their offspring exemplify it by tending to exhibit the same deviation from the parental stock as themselves. Indeed, there seems to be in many instances a prepotent influence about a newly arisenvariety which gives it what we may call an unfair advantage over the normal descendants from the same stock. This is strikingly exemplified by the case of Gratio Kelleia, who married a woman with the ordinary pentadactyle extremities and had by her four children, Salvator, George, André, and Marie. Of these children Salvator, the eldest boy, had six fingers and six toes, like his father; the second and third, also boys, had five fingers and five toes, like their mother, though the hands and feet of George were slightly deformed; the last, a girl, had five fingers and five toes, but the thumbs were slightly deformed. The variety thus reproduced itself purely in the eldest, while the normal type reproduced itself purely in the third, and almost purely in the second and last; so that it would seem, at first, as if the normal type were more powerful than the variety. But all these children grew up and intermarried with normal wives and husbands, and then note what took place—Salvator had four children, three of whom exhibited the hexadactyle members of their grandfather and father, while the youngest had the pentadactyle limbs of the mother and grandmother; so that here, notwithstanding a double pentadactyle dilution of the blood the hexadactyle variety had the best of it. The same prepotency of the variety was still more markedly exemplified in the progeny of two of the other children, Marie and George. Marie (whose thumbs only were deformed) gave birth to a boy with six toes, and three other normally formed children; but George, who was not quite so pure a pentadactyle, begot, first, two girls, each of whom had six fingers and toes; then a girl with six fingers on each hand, and six toes on the right foot, but only five toes on the left; and lastly, a boy with only five fingers and toes. In these instances, therefore, the variety, as it were, leaped over one generation to reproduce itself in full force in the next. Finally, the purely pentadactyle André was the father of many children, not one of whom departed from the normal parental type.’
‘The first of them is that of the “Ancon,” or “Otter” sheep, of which a careful account is given by Colonel David Humphreys, F.R.S., in a letter to Sir Joseph Banks, published in thePhilosophical Transactionsfor 1813. It appears that one Seth Wright, the proprietor of a farm on the banks of the Charles River in Massachusetts, possessed a flock of fifteen ewes and a ram of the ordinary kind. In the year 1791, one of the ewes presented her owner with a male lamb differing, for no assignable reason, from its parents by a proportionally long body and short bandy legs, whence it was unable to emulate its relatives in those sportive leaps over the neighbours’ fences, in which they were in the habit of indulging, much to the good farmer’s vexation.
‘With the ’cuteness characteristic of their nation, the neighbours of the Massachusetts farmer imagined it would be an excellent thing if all his sheep were imbued with the stay-at-home tendencies enforced by nature upon the newly arrived ram, and they advised Wright to kill the old patriarch of his fold, and install the Ancon ram in his place. The result justified their sagacious anticipations.... The young lambs were almost always either pure Ancons or pure ordinary sheep. But when sufficient Ancon sheep were obtained to interbreed with one another it was found that the offspring was always pure Ancon.’
‘The second case is that detailed by a no less unexceptionable authority than Réaumur, in hisArt de faire éclore les Poulets. A Maltese couple named Kelleia, whose hands and feet were constructed upon the ordinary human model, had born to them a son, Gratio, who possessed six perfectly moveable fingers on each hand, and six toes, not quite so well formed, on each foot. No cause could be assigned for the appearance of this unusual variety of the human species. But however they may have arisen, what especially interests us is to remark that, once in existence, varieties obey the fundamental law of reproduction, that like tends to produce like, and their offspring exemplify it by tending to exhibit the same deviation from the parental stock as themselves. Indeed, there seems to be in many instances a prepotent influence about a newly arisenvariety which gives it what we may call an unfair advantage over the normal descendants from the same stock. This is strikingly exemplified by the case of Gratio Kelleia, who married a woman with the ordinary pentadactyle extremities and had by her four children, Salvator, George, André, and Marie. Of these children Salvator, the eldest boy, had six fingers and six toes, like his father; the second and third, also boys, had five fingers and five toes, like their mother, though the hands and feet of George were slightly deformed; the last, a girl, had five fingers and five toes, but the thumbs were slightly deformed. The variety thus reproduced itself purely in the eldest, while the normal type reproduced itself purely in the third, and almost purely in the second and last; so that it would seem, at first, as if the normal type were more powerful than the variety. But all these children grew up and intermarried with normal wives and husbands, and then note what took place—Salvator had four children, three of whom exhibited the hexadactyle members of their grandfather and father, while the youngest had the pentadactyle limbs of the mother and grandmother; so that here, notwithstanding a double pentadactyle dilution of the blood the hexadactyle variety had the best of it. The same prepotency of the variety was still more markedly exemplified in the progeny of two of the other children, Marie and George. Marie (whose thumbs only were deformed) gave birth to a boy with six toes, and three other normally formed children; but George, who was not quite so pure a pentadactyle, begot, first, two girls, each of whom had six fingers and toes; then a girl with six fingers on each hand, and six toes on the right foot, but only five toes on the left; and lastly, a boy with only five fingers and toes. In these instances, therefore, the variety, as it were, leaped over one generation to reproduce itself in full force in the next. Finally, the purely pentadactyle André was the father of many children, not one of whom departed from the normal parental type.’
169. The instances now quoted illustrate two things. Both tell us how varieties arise, we may say spontaneously, or in other words we cannot tell how; and the former instance, that of the Ancon breed, showsus moreover that such varieties when they do occur may be rendered permanent by means of artificial selection. If the six-fingered descendants of Gratio Kelleia had been forced to intermarry amongst themselves it is highly probable that we should have had a permanent hexadactyle variety of the human race. It has likewise been shown by Charles Darwin that the pouter, the fan-tail, the carrier, and the tumbler are all varieties of the common rock-pigeon.
170. It thus appears that permanent varieties may be produced by artificial selection. Now Darwin and Wallace have brought before us the very great fact that similar changes can also be produced by natural selection.
To illustrate this, let us imagine a slight variety to arise spontaneously, we do not know how. Having arisen there is a ‘prepotent influence’ about it which enables it to secure a considerable proportion of offspring having its own characteristics. Now, suppose that the characteristics are such as to adapt the individuals possessing them more perfectly to the conditions of nature which surround them. When, by breeding amongst themselves, the new variety is rendered permanent, the members of this variety will, therefore, have an advantage over their elder brethren so far as certain conditions of nature are concerned, will in fact succeed better in the struggle for existence, and will ultimately displace the elder branches. Thus the struggle for existence bears to natural selection the same relation as man bears to artificial selection.
171. We now come to the real point of difficulty, or at least the unproved point, in the Darwinianhypothesis. We may cross one race with another, but we do not obtain, so far as we know, those phenomena of infertility which are exhibited when we cross distinct species with each other. The Ancon sheep were perfectly fertile when matched with their elder brethren, and the dray-horse and the Arab, or the pouter and the tumbler, breed together as easily as if they were of the same race. But if we cannot produce infertility, how can we apply the results of artificial selection to account for the origin of species?
This difficulty is met by Darwin and his followers in this way:—‘It is not as yet proved,’ says Professor Huxley, ‘that a race ever exhibits, when crossed with another race of the same species, those phenomena of hybridisation which are exhibited by many species when crossed with other species. On the other hand, not only is it not proved that all species give rise to hybrids infertileinter se, but there is much reason to believe that, in crossing, species exhibit every gradation from perfect sterility to perfect fertility.’ This appears to carry weight; the old theory went with a leap from perfect fertility to perfect sterility, and did not contemplate the possibility of a continuous gradation from the one extreme to the other; at least its argument was founded upon the neglect of such a gradation. But if there be a gradation of this kind, it follows that infertility will merely represent the results of crossing two species whose functional characteristics are very different from each other; and, on the other hand, the reason why artificially produced varieties are not infertile when crossed with one another may only bethat the experiment has not been continued long enough.
Time, in fact, is the essential requisite in all such attempts to imitate nature.
172. In connection with this subject, Mr. Darwin has remarked that certain plants are more fertile with the pollen of another species than with their own; and Professor Huxley tells us that there are certainfuciwhose male element will fertilise the ovule of a plant of distinct species, while the males of the latter species are ineffective with the females of the first. So obscure in some of its branches is the working of the reproductive system.
Again, the following remark by Mr. Darwin is verysuggestive:—
‘First crosses between forms known to be varieties, or sufficiently alike to be considered as varieties, and their mongrel offspring, are very generally, but not quite universally, fertile. Nor is this nearly general and perfect fertility surprising, when we remember how liable we are to argue in a circle with respect to varieties in a state of nature; and when we remember that the greater number of varieties have been produced under domestication, by the selection of mere external differences, and not of differences in the reproductive system. In all other respects, excluding fertility, there is a close general resemblance between hybrids and mongrels.’
173. The result of all these speculations is to render it probable that there may be in nature, give it time enough, a process which leads to the transmutation of species.
The accumulation of successive differences, eachrepresenting some element of success in the struggle for life, may easily be imagined to be capable of producing, in the course of ages, a very great change.
Reasoning out this hypothesis, the more advanced followers of Mr. Darwin do not hesitate to describe all the varieties of living things, including man, as the results of development from some primordial germ taking place throughout the course of immeasurable ages. And Mr. Darwin himself, in his work on the Descent of Man, lays great stress on the occurrence of homologous structures in man and the lower animals, as well as on the development in man of rudimentary structures, which are either absolutely useless to their possessor, or of very slight service indeed, but which appear to serve as an index of the various stages through which the human species has passed in its progress upwards from lower forms of life.
174. Mr. Wallace, however, sees in the production of man the intervention of an external will.
He remarks that the lowest types of savages are in possession of a brain, and of capacities far beyond any use to which they could apply them in their present condition, and that therefore they could not have been evolved from the mere necessities of their environments.
175. Finally, Professor Huxley imagines the possibility of the Darwinian hypothesis requiring modification. Alluding to the assumed circularity of the planetary orbits which followed the establishment of the Copernican hypothesis (Art. 69), heremarks:—
‘But the planetary orbits turned out to be not quite circular after all, and, grand as was the serviceCopernicus rendered to science, Kepler and Newton had to come after him. What if the orbit of Darwinism should be a little too circular? What if species should offer residual phenomena, here and there, not explicable by natural selection? Twenty years hence naturalists may be in a position to say whether this is, or is not, the case; but in either event they will owe the author of “The Origin of Species” an immense debt of gratitude.’
176. We will defer to our last chapter some further remarks on Mr. Darwin’s hypothesis. Meanwhile, before concluding, let us briefly allude to the original production of living things on our globe. It may, perhaps, eventually be possible by means of a hypothesis of evolution, to account for the great variety of living forms on the supposition of a single primordial germ to begin with; but the difficulty still remains how to account for this germ.
It is against all true scientific experience that life can appear without the intervention of a living antecedent. How then are we to explain the production of the primordial germ?
The difficulty of doing so from our point of view would appear to be unusually great, for we have come to the conclusion that, as a matter of scientific principle, we cannot admit any such breach of continuity as a pure act of creation in time would imply.
If, then, a pure act of creation in time be an inadmissible hypothesis, and if the hypothesis of Abiogenesis be equally inadmissible, our readers may well ask how are we to surmount the difficulty. For our reply to this question, we must once more beg to refer them to our concluding chapter.