Chapter VI: Appendix: I. Relations of Science and Religion 313 (4)

Among these results is _rejection of fixedness of species_ as implying impossibility of deviation from a single normal type of structure. The possibility of adaptive changes being granted, the absolute fixedness of species in the rigid sense formerly acknowledged is abandoned. How great the modification of view must be, is much more difficult to decide, and hardly admits of exact statement. There is certainly no denial of distinction of species, nor can such denial ever find acceptance, whatever be the advance of theory, for the distinctions are so broad as to render this impossible. But the whole work of classification of the different orders of animal life, exceedingly difficult in any case, has been rendered much more perplexing in consequence of the accumulation of evidence favoring the doctrine of evolution. What can properly be regarded as the origin of a new species, and what as a mere modification or advance in a species already recognized, are questions for which it is difficult to find an exact answer. The theory of the "origin of species" by natural selection seems placed in an awkward perplexity as to what constitutes _origin_ of a new order of life. And this difficulty must be regarded as a constant attendant on the scheme of thought, since "adaptive changes" must be of slow progress, and historically obscure, inasmuch as a succession of very slight differences must contribute to a general result. In this way it may even become matter of keen discussion what actually constitutes organic advance. Mr. Darwin admits serious difficulty at this point. He says, "Here we enter on a very intricate subject, for naturalists have not defined to each other's satisfaction what is meant by an advance in organization."[BK] Thus there is dispute among competent authorities as to which may properly be considered the highest order of plants, and which the highest order of fishes. On the other hand, it is comparatively easy to decide among the more highly organized animals, when an advance is made, by reference to increased complexity in structure, or provision of separate organs for accomplishment of distinct functions. These considerations, however, suffice to indicate how many and complicated are the subjects requiring to be examined on evidence, and adjusted in their relations to each other, before it can be possible to get beyond surmise, in order to formulate a complete scientific theory. That "adaptive changes" by natural law of evolution are not only possible, but that they frequently occur under observation, admits of no question; but whether this includes changes of structure such as imply origin of species may still be subject of grave doubt. The alterations made by Mr. Darwin in successive editions of his book, from the first edition in 1859, to the sixth edition in 1872,[BL] introduced, as he explains, "according as the evidence has become somewhat stronger or weaker," are sufficient to suggest that a vast amount of work remains to be done before a well-defined theory can be formulated. While there is universal agreement as to the possibility of "adaptive changes" to which Mr. Darwin provisionally restricted his theory on account of the investigations of Nageli as to plants, and those of Broca as to animals, there is much diversity of opinion concerning the wider application of the theory of evolution. This diversity arises in part from the varying estimate of the value of evidence as now accumulated, and in part from the varying conception of the completeness of our records of the ancient history of organism as presented by geology. There is as yet no general consensus of opinion, nor is there likely to be for a long time to come. Mr. Darwin himself is sufficiently cautious and faithful to observational methods, to admit that there are serious difficulties, of some of which he ventures only to say that they "are greatly diminished," while some have disappeared. Other writers, such as Hæckel, with greatly less caution, and with much greater alacrity in leaping over chasms, are prepared to go much further and faster than Darwin. Many more are exceedingly doubtful as to the scientific value of the evidence at command, being, as Mr. Darwin has said, "much shaken in their former belief."[BM] And of many it must be said that they are convinced that the evidence is far from warranting the conclusion that all organized existence can be traced to "only a few forms," or to "one," according to the alternatives suggested by Darwin in the closing sentence of his book.

Waiving, then, meanwhile, as the state of scientific evidence warrants us to do, the question of the probable number of primordial forms in which organized existence appeared, there is at least another definite result to be recorded as following from even a modified recognition of a theory of development, that is the _rejection of belief in the simultaneous origin of all species_ or orders of animal life existing now in the world. The scientific conception of the history of animal life is, that there has been a historical progression in the appearance of animals, in so far as lower orders took precedence of higher, while the higher have shown large power of adaptation to the circumstances in which they have been placed. In accordance with the whole principles regulating the relations of religion and science, religious men, scientific and non-scientific, will readily acquiesce in this modification of general belief, as largely favored by evidence which geology supplies, and supported by testimony drawn from the actually existing order of things; and they will do so with clear recognition that this view involves no conflict with scriptural statement, and is so far from containing in it any thing antagonistic to the fundamental conception of the supernatural origin of existence, that it harmonizes with it, even intensifying the demand upon a transcendent cause for the rational explanation of the admitted order of things.

Having thus indicated in definite form the favorable impression made on the public mind by the theory of evolution under a law of natural selection, it will suffice to indicate very briefly the more prominent difficulties with which the theory has grappled, but from which it has not escaped. In doing so, it should be said that the careful and deliberate manner in which Mr. Darwin has faced the host of difficulties which have gathered around is deserving of highest praise, as in harmony with the scientific spirit, and in marked contrast with the light-and-go-easy style in which others, such as Hæckel, and even Schmidt, pass over the ground, announcing things as undoubted facts, and even "self-evident" truths, of which no man can speak with any degree of certainty. On the other hand, it seems a reasonable ground of complaint against many opponents of the theory, which Mr. Darwin urges specially against Mr. St. George Mivart, that it is no part of their plan "to give the various facts and considerations opposed to their own conclusions," while marshalling the difficulties against an evolution theory. And yet it should be remembered that a great service is done to science in a period of transition, when difficulties are powerfully urged against a popular hypothesis, as an injury is done to science by precipitate and ill-considered arguments in support of such a hypothesis.

Of the most serious difficulties in the way of a theory of descent by evolution, the _first_ concerns _the nature of the evidence_, inasmuch as all change coming under observation does not indicate progression or improvement in the organism. The importance of this may be best indicated by quoting Mr. Darwin's explanatory words as to alterations in the fifth edition of his book on species. He says, "In the earlier editions of my _Origin of Species_, I probably attributed too much to the action of natural selection or survival of the fittest. I have altered the fifth edition of the _Origin_ so as to confine my remarks to adaptive changes of structure. I had not formerly sufficiently considered the existence of many structures, which appear to be, as far as we can judge, neither beneficial nor injurious, and this I believe to be one of the greatest oversights as yet detected in my work." When it is certain that deviation from the normal structure may take place which is a disadvantage to the individual, and that this may descend to offspring; when it is also shown that deviation may occur which appears to serve no end, that is, contributes to no phase of functional activity; when besides advantages gained are lost, and the race returns to its original type of structure; and when farther there are examples of degeneration, as in parasitic races,--such facts interpose special difficulties in the way of an all-embracing theory of progress by natural selection. Besides, as deviations occur of an unfavorable kind among domesticated animals under the care of man, it becomes obvious that progress may be readily lost even in most favorable circumstances.

The next outstanding difficulty is that of _meeting the requirements of logical inference_. This has been specially urged by Mr. Mivart as bearing upon the "incipient stages" of advance, and the difficulty certainly presses heavily at that point. Natural selection may account for much in the history of higher organisms where powers of sensibility and locomotion are great, but how can we find in natural selection an adequate explanation of progress in organisms within which these powers are at the lowest. The difficulty is to get a cause sufficient to account for the start of a movement so vast as that which is to culminate in man. Mr. Darwin feels the force of this difficulty, and replies thus, "as we have no facts to guide us, speculation on the subject is almost useless."[BN] But this perplexity which is most glaring at the beginning of the upward course, clings to the theory at every stage in the combination of struggle and improvement,--descent involving a real _ascent_. Whether the organism be more or less complex, it depends upon _external causes_ for its improvement, and the dependence continues at every stage. Granting that there is everywhere struggle for existence and survival of the fittest, are these sufficient to account for results so great as are involved in unceasing advance of organism?

If it be argued that they are sufficient, a serious perplexity comes from the opposite quarter,--How does it happen that all organic existence does not advance together to a common elevation? If the theory accounts for advance, how shall we account for the want of it? The difficulties are as great for the theory in view of the large body of facts it does not attempt to include, as in the facts it strives to embrace. Agassiz put this difficulty with much force in 1857, and it has not received any satisfactory answer. He said, "It is a fact which seems to be entirely overlooked by those who assume an extensive influence of physical causes upon the very existence of organized beings, that the most diversified types of animals and plants are everywhere found under identical circumstances."[BO] If, as Mr. Darwin says, "looking to the first dawn of life," we may believe that "all organic beings presented the simplest structure"; if the struggle for existence is uniformly encountered and leads to survival of the fittest, how is it that within the same area, organism has not advanced to similar complexity? If under constraint of the evidence for the theory, we surrender the doctrine of inevitable fixedness of species, how shall we nevertheless account for the permanence of species? It is not suggested that there is at successive stages "new and simple forms continually being produced by spontaneous generation." This hypothesis of Lamark is rejected by Mr. Darwin,[BP] as it is by almost all scientific observers? How, then, can we explain the facts? We are told that certain orders have "fallen out" in the march of progress; but we need a scientific account of this which shall harmonize with a theory of action of environment, and such an account is not forthcoming. It may be said that the very success of the theory by accumulation of most striking and important evidence, is bringing it into difficulty, and suggesting its insufficiency. The more powerful and imposing the action of the law of natural selection, the more pressing becomes the need for a scientific explanation, at once distinct and harmonious, which will account for the persistence of species, when struggle for existence goes on under similar or even analogous action of environment. The presence everywhere of these lower forms alongside of the higher, adds greatly to the attractiveness of nature, and not even the grandeur of a universal advance towards the higher levels of organization would make up for the disappearance of the marvels of lower orders of animals. A monotony of grandeur may compare unfavorably with the wealth of variety and adversity; and so a law of continuity or persistence may be found adding to the greatness of a universe in which a law of progress or evolution also finds uniform application.

Upon this contrast between persistence and progress, general attention will henceforth be concentrated in judging of the place and value of a theory of descent. There is no need for hurry or impatience in this matter. The words of Mr. Darwin will find ready assent as he says, "No one ought to feel surprise at much yet remaining unexplained on the origin of species, if we make due allowance for our profound ignorance on the mutual relations of the inhabitants of the world at the present time, and still more during past ages."[BQ] In accordance with this acknowledgment, a wide range of scientific research still remains to be undertaken, and religious thought can have nothing but friendly interest in the work, as it may well be assured of drawing thence fresh contributions of great value for higher speculation concerning the government of the universe.

FOOTNOTES:

[AO] Tait's _Recent Advances_, p. 23.

[AP] Lyell's _Elements of Geology_, p. 2.

[AQ] _Recent Advances_, p. 24.

[AR] _Doctrine of Descent_, p. 20.

[AS] _Ib._ p. 161.

[AT] _Introduction to the Theory of Science_.

[AU] _Doctrine of Descent_, p. 163.

[AV] _Doctrine of Descent_, p. 162.

[AW] _Origin of Species_, p. 577.

[AX] See Appendix VII.

[AY] See Appendix V.

[AZ] See Appendix IV.

[BA] _Origin of Species_, p. 577.

[BB] _The Origin of Species_, xiii. 4th ed.

[BC] _The Origin of Species_, p. 1.

[BD] _Malay Archipelago_, 1869.

[BE] The passage is quoted as given by Schmidt in his _Doctrine of Descent_, p. 132. Italics are inserted to guide the eye of the reader to the successive stages.

[BF] Referring to organized being.

[BG] _Origin of Species_, p. 577.

[BH] _Doct. of Descent_, p. 161-2.

[BI] _Origin of Species_, 4th ed. p. 143.

[BJ] _Doct. of Descent_, 162.

[BK] _Origin of Species_, 4th ed. p. 141.

[BL] It may be well to mention here that the _third_ American edition is from the _fifth_ English edition.

[BM] _Origin of Species_, 6th ed., p. 289.

[BN] _Origin of Species_, 6th. ed. chap. iv. p. 100.

[BO] _Contributions to the Natural History of the United States_, Introduction, Boston, 1857; and _Essay on Classification_, p. 15, published separately; London, 1859. See Appendix VI.

[BP] _Origin_, 4th ed. p. 143.

[BQ] _Origin of Species_, 6th. ed. chap. iv. p. 100.

LECTURE V.

RELATIONS OF LOWER AND HIGHER ORGANISMS.

From the general aspects of the theory of species, we pass to the consideration of distinct groups of organism, with the view of ascertaining their relations to each other. In doing so, it is better to begin at the lower end of the scale, leaving for a more advanced stage of inquiry the higher types of organism. In this department of the subject, special obligations are due to the wide range of investigations either occasioned or stimulated by the theory of evolution. For, whatever may be the ultimate award passed on this theory, there will be a unanimous recognition of the great value to science attending on the varied forms of inquiry stimulated by the writings of Mr. Charles Darwin. And one obvious and strong reason for such acknowledgment is that so many of the results of these researches have an inherent value quite distinct from their testimony in favor of the theory that the struggle for existence is the principal factor in the origin of new species.

One of the most interesting fields of observation thus opened, is that concerned with the fertilization of plants by the intervention of insects and birds. A beginning in this department was made by the German naturalist, Christian Konrad Sprengel, who published in 1793 the report of his observations. In this he has been followed by Darwin, in 1862; by Dr. Hooker, Professor Asa Gray whose contributions appeared in the _American Journal of Science and Art_ in 1862, and 1863, Moggridge, Fritz Müller, and Sir John Lubbock. The facts now accumulated, rank as an important contribution to botany and zoölogy, and naturally fall within the circle of recent advances to which it is desirable that attention be turned.

The general result is one of great interest, as illustrating a striking degree of interdependence between lower and higher organisms,--the vegetable and animal kingdom contributing to each other's subsistence and propagation. Flowers present special attractions to insects flying around, alluring them by varied colors, and providing for them by secreting stores of honey; on the other hand, these insects (flies, bees, wasps, etc.), seeking the honey which satisfies their wants, at the same time carry the pollen from one flower to another, thus providing for the fertilizing of the plants. In some cases, fertilization is secured by a natural process within the organism itself; in other cases, the pollen is scattered over a region by the wind; but the most wonderful, and at the same time efficient mode of providing for the growth of vigorous plants, is fertilization by the agency of insect life.

A brief outline of the ordinary structure of the flower will introduce to a ready appreciation of the scientific interest attaching to this last mode of fertilization, both as concerning the functions of different portions of the flowers, and the relation of dependence established between higher and lower forms of organism, so that each is dependent on the other.

Every flower as it unfolds from the bud, consists of a series of whorls, or layers of substance twined or twirled round in such a manner as to unfold or coil back, as the flower opens. The _outermost_ of these whorls (_calyx_) is a mere covering or sheath, usually of a green color, which protects the bud during the more tender period, curling up and withering as the flower opens, spreading forth its beauty. The _second_ whorl (_corolla_) is what we more commonly regard as the flower proper, the colored leaves, or cup, or bell, according to the specific shape distinguishing the plant. The _third_ whorl consists of a series of stalks or filaments (_stamens_) which as the flower matures or ripens stand up distinct from each other, each one having at its summit a little tuft or cushion (_anther_) covered with a fine dust or powder (_pollen_). The _fourth_ or inner-most whorl, the centre piece of the flower (_pistil_) is that in which the seed is generated and brought to maturity. We may thus say of the flower, that its outermost whorl is a temporary covering which withers and shrinks out of view, when the beauty of the inner structure is laid open; that the second is that which attracts the eye by the loveliness of its hues; while the two which belong to the internal structure of the flower are concerned with the reproduction or propagation of the plant, providing for the healthy germ from which a fresh plant of the same order may spring up. The relation of the fine yellow powder produced at the tips of the third whorl, to the seeds which are gathered together within the fourth whorl, is the matter to which special attention has been directed by the recent discoveries which have rewarded patient research. The fine powder or pollen needs to be carried to the seed, so that its properties may operate upon that seed, if it is to be fertilized, or so matured, as to fulfil its function in generating a new plant when it is committed to the soil. In many cases it is enough that the fine powder should fall down from its elevation on the seeds below. This is self-fertilization, and is easily provided for by the mere bending of the head of the flower as it approaches maturity, or by the swaying of it in the breeze. But a more difficult, and as we might be inclined to add, more precarious, because less certain, method for fertilization is required in many cases. The experiments carried on by all our gardeners, and in a still more extended scale in all our centres of botanic research, have established the fact that in many cases, the yellow powder of one plant must be in some manner carried over to the seed produced within another flower, if that seed is to yield a satisfactory result to the horticulturist.

We have thus two prominent facts here. The one is _the essential importance of the pollen_ for fertilization; and the other, _the need for the transference of the pollen_ from one plant to another in order to secure reproduction of vigorous growth by the sowing of the seed. As to the first, the pollen, which appears a fine powder or flour contains fluid protoplasm, that which Professor Huxley has described as the "single physical basis of life under all the diversities of vital existence."[BR] These pollen grains falling on the seed discharge their protoplasmic fluid upon it, and by this means contribute to fertilization. This original or primordial form of vitalising agency is carried from one part of the flower to another, and this transference is the law regulating the propagation of flowering plants.

But, just at this point, we come upon the most striking results of recent research. Though all pollen is of this primary nature, named protoplasm, it is not found to hold true that pollen is of the same value for fertilization from whatever quarter it comes. On the contrary, most important differences result according to the source of the pollen. There is first the process of self-fertilization. But in many cases,--Mr. Darwin has shown that this holds of the majority of the orchids,--transference of the pollen from one plant to another proves to be a great advantage, if not an actual necessity for propagation of the plant. This process, known as cross-fertilization, gives a healthy and vigorous growth; want of it, will lead to degeneration, and ultimate extinction. This discovery has introduced a whole series of the most striking observations, throwing a flood of light on the distribution and interdependence of distinct forms of organism. The necessary relation between the pollen and the seed having been acknowledged, and next the value of transference of pollen from one plant to another, the first step in the line of discovery was made by the observation of a natural provision to _prevent self-fertilization_ by rendering it impossible that the pollen of a plant should fall on the seed of that plant. This entrance on the line of discovery was made by Sprengel so far back as 1790, by whom it was observed that in many plants the pollen and the seed did not come to ripeness at the same time.[BS] In some cases, the pollen is ripened before the seeds are ready; in other cases, the order of events is reversed. This observation naturally suggested transference of pollen from one plant to another; and this, connected with the continual coming and going of flies, bees, and butterflies, led to the further discovery, that _insects_ unwittingly perform a large part of the work needful in order to _provide for fertilization_. Mr. Darwin has pointed out that from the paper of Robert Brown in the _Linnean Transactions_, in 1833; and from that of Dr. Hooker in the _Philosophic Transactions_ for 1854, the peculiar phenomena had begun to awaken scientific interest. It was, however, when the researches as to origin of species had given fresh motive to observation concerning the relations of different types of organism, that the whole facts were brought to view, separately recorded, and at length systematized so as to lead to their full interpretation. Mr. Darwin himself concentrated on the orchids as peculiarly interesting and suggestive, while a host of workers all over the world were turning their energies into this new field of observation which promised ample return for patient research.

As a reward of these investigations important facts have been established on ample evidence. First, it has been confirmed by varying lines of evidence that transference of pollen, or cross-fertilization, is of special value in the development of plant life. Investigation has strengthened the evidence of disadvantage arising from fertilization by exclusive dependence on self-produced pollen. Fritz Müller has recorded a variety of observations that the pollen of some flowers has so little influence on the seed produced on the same stem that when it falls upon the seeds no effect is produced; the pollen lies there as if possessed of no more vitalizing power than grains of dust. And, what is even more surprising, Müller has found examples in which the pollen does act upon the seeds of its own flower, but acts _injuriously_, insomuch that the flower, the pollen, and the seed-producing portion of the plant begin to decay.[BT] So deep has been the impression made on Mr. Darwin's mind by the evidence of provision for transference of pollen, that he closes his valuable and interesting book on the _Fertilization of Orchids_ with the following statements. Having remarked that "self-fertilization would have been an incomparably safer and easier process than the transportal of pollen from flower to flower," he adds these words,--"It is hardly an exaggeration to say that Nature tells us, in the most emphatic manner, that she abhors perpetual self-fertilization."[BU]

The next result secured presents an important relation between animal life and vegetable. These flowers do not depend for their fertilization upon the action of the wind, which in scattering profusely in all directions must occasion large waste of pollen. There is found to be distinct provision for carrying the pollen from one flower to another by insects, such as the bees, whose industry in gathering honey has been celebrated from ancient times, specially because of our interest in the storehouse, but with little suspicion of the double work being done by the bees, who add to their other industry that of horticulturists. These bees are the pollen-bearers,--the recognized local carriers, regularly on the road,--doing the work which the flowers, in lack of locomotive power, could not do for each other. Or, looking at the relation of things from another point of view, the bees are at the same time gathering the honey, and sowing the seed for a future harvest. This reference to the honey, however, introduces to notice a companion series of facts, showing the provision in completed form for an interchange of services. The plants supply an attraction to the animals, while the animals render a service to the plants. This phase of interdependence is made more conspicuous by the contrast apparent in the structure and functions of plants fertilized by the wind, such as the larger shrubs and trees, which as they present a greater surface to the breeze, do not call for the same detailed provision for carrying the pollen. In contrast with these more bulky representatives of the vegetable kingdom, the more lowly and insignificant in size, as well as more short-lived, present many attractions in color, scent, and secretion of honey, all adapted to the nature of insects, suited for the work of pollen carrying. The attractions of form, color, and scent in the flowers are well known to us; but they are also appreciated by the insects,--a fact which may possibly suggest that a high degree of intellectual power is not required for appreciation of these qualities, as no one professes that bees rank high intellectually. At the same time, if comparisons are to be made at this point, the farther suggestion may also be introduced, that there is little testimony to intelligence where search for food is concerned, and while the human race do not feed on flowers, insects are constantly feeding from them. The attractions in the two cases therefore vary considerably in their significance. Restricting attention, however, to the special field of observation now before us, with the view simply of ascertaining the relations of plants and insects, color and honey present the two most prominent attractions accounting for the perpetual hum of life heard amongst the flowering plants. Different parts of the flower provide for variegated coloring, and stores of honey; these present attractions to the insects; and the structure of the flowers as they provide for the landing of the insects, and require that they penetrate to their centre for the secreted honey, secures that the work needful for fertilization be effectually done. This last feature of adaptation is that on which attention may be specially concentrated here. Mr. Darwin in treating of orchids has described this part of their structure in these words;--"In almost all the species, one of the petals (or leaves of the flower) which is properly the upper one, is larger than the others and stands on the lower side of the flower, where it offers a landing-place for insects."[BV] Towards the inner or root end of this leaf (_labellum_) is the gland, in some flowers appearing only as a slit, in others forming like a tube, (_nectary_) which secrets the honey. Just over the entrance to the part where the honey is to be found stands that which secrets the pollen prepared for fertilizing some other flower. So soon as the bee or other insect presses its head well into the centre of the flower, some of the pollen adheres to it; when the head is withdrawn, this pollen is borne off to the flower which the bee next visits; and as the head is pressed into the core of this flower the pollen is deposited, and provision for fertilization is complete. Special features appearing in certain classes of the orchids illustrate how it is possible for the bee so laden to visit many flowers without depositing the pollen, yet a little later accomplish the object quite simply. The following illustration from Mr. Darwin's account of the first orchid selected, will suffice. Just _above_ the entrance to the honey store, lies a pouch connected with the pollen store. As the head of the bee is pressed down towards the honey, this pouch is burst open, and from it issues a little sticky gland or disc, or it may be two of these discs. These adhere at once to the head of the bee, and being connected by a slight band with packets of pollen grains so soon as the animal retires the pollen is drawn with it, standing out like a seed vessel on the head. The strangest part of the contrivance appears in what thereafter follows. "The viscid matter has the peculiar chemical quality, of setting like cement, hard and dry in a few minutes." Suppose both the little viscid balls have been withdrawn, the bands bearing the pollen will appear "projecting up like horns." "How then can the flower be fertilized? This is effected by a beautiful contrivance; though the viscid surface remains immovably affixed, the apparently insignificant and minute disc of membrane to which the caudicle adheres is endowed with a remarkable power of contraction, which causes the pollinium to sweep through an angle of about ninety degrees, always in one direction towards the apex of the proboscis, in the course of thirty seconds on an average."[BW] That is, the two erections bearing packets of pollen which formerly stood up almost perpendicular, like horns, begin to lower until they reach the horizontal; in this way when the bee enters a flower the packets of pollen inevitably touch the seed stores, communicating what is required for their fertilization. Nor have we even yet the whole of the contrivances adapted for this end. "Here comes into play another pretty adaptation." The seed vessel to be fertilized is very sticky, "but not so viscid as when touched by a pollinium to pull the whole off an insect's head." But it is sufficiently adhesive "to break the elastic threads by which the packets of pollen grains are tied together." In this way, it tears off so much from the store adhering to the head of the bee, and still leaves there what may supply the requirements of many flowers besides. The description thus given will suffice to indicate how close is the relation of the lower orders of animal life with vegetable life, and will illustrate how the lower organism may be dependent for existence on the higher, an illustration in some respect the converse of the facts illustrating origin of species by development.

There remains in this department of inquiry only one additional set of facts, to which reference may be made, as illustrating _distribution of work among insects and birds_, assigning them to different orders of plants. This will illustrate contrivance on a still wider scale, discovering distinct sets of affinity, which imply common localization for given plants and animals. In this it appears that flies, humble bees, and birds with long slender bills, such as the humming birds, all have a share in the work required for fertilizing plants.

There is one example, _epipactis latifolia_, with a cup-shaped labellum, in which honey is secreted, and which bees are never seen to frequent. What, however, the bees pass, the wasps suck eagerly, and by them it is fertilized. Of this flower, Mr. Darwin says,--"It is very remarkable that the sweet nectar of this _epipactis_ should not be attractive to any kind of bee. If wasps were to become extinct in any district, so probably would the _Epipactis Latifolia_."[BX]

Another example there is of an orchid _(Spiranthes Autumnalis_), commonly known as _Ladies' Tresses_, having a series of spikes, of which the lowest flowers are first matured, the others following in order as they rise towards the summit. This plant is frequented by bees, whose practice it is to begin with the lowest flowers and ascend gradually to the top. This order in seeking to extract the honey, proves to be the proper one for fertilizing of the plant, because the pollen which the bee brings will be received by the riper flower on which it lands, and when that has been deposited, fresh pollen will adhere to the bee as it rises to the less matured flowers, and thus it departs laden with pollen destined for the lowest flowers of the next plant it visits.[BY]

These examples introduce us to a general plan for fertilization of plants by the intervention of insects, so complete in the order of distribution that we may classify the plants according to the insect by which they are fertilized, making it natural to speak of fly orchids, spider orchids, wasp orchids, and bee orchids. In all cases the search for honey determines the visits made, leaving still unexplained, however, the fact that the nectar of some plants is shunned by certain insects, and eagerly absorbed by others. With the general source of attraction in the flowering plants, there are diversities of arrangement among the insects, according to the comparative size of the flower, and strength required in order to penetrate to the inner chamber where the honey is stored. Because of the minuteness of the aperture, there are flowers from which the bee can not draw supplies; on the other hand, because of the size and strength of the flower, there are cases in which the ordinary bee is incapable of reaching the store, and the stronger humble bee alone succeeds in effecting an entrance.

There is thus presented in mere outline a general view of the interdependence of lower and higher orders of organism. While each flower develops pollen and seed, there are arrangements connected with the ripening of these two, which restrain or even prevent self-fertilization. Along with this there are distinct lines of evidence to establish the rule that cross-fertilization, or transference of pollen from one flower to the seed of another, secures the growth of a much healthier and more vigorous order. Where such transference is provided for otherwise than by the wind, the attractiveness of the flowers brings to them at the proper season, the insects which carry the pollen, and to each class of insect is distributed a distinct share in the work. In these facts we have a natural law for preservation of species, discovering in a very striking manner the dependence of lower organism on higher. As Mr. Darwin has said,--" The _meaning_ of these facts is clear." Referring to the examples in which the insects have to bore holes in order to reach the honey, where there is need for time to allow for the hardening of the viscid matter, he has used the following words which are most fitly applied,--"If this double relation is accidental, it is a fortunate accident for the plants; but I can not believe it to be so, and it appears to me one of the most wonderful cases of adaptation which has ever been recorded."[BZ] It is most obviously true, as Sir John Lubbock has said, that "neither plants nor insects would be what they are, but for the influence which each has exercised on the other."[CA] In view of the facts here very briefly described it will generally be allowed that Mr. Darwin's expectation from the study of orchids will be verified,--"An examination of their many beautiful contrivances will exalt the whole vegetable kingdom in most persons' estimation."[CB] We have enough before us to enable us to appreciate our author's feeling when he says, "Hardly any fact has struck me so much as the endless diversities of structure,--the prodigality of resources for gaining the very same end."[CC] Again when giving us his prevailing impression he says,--"The more I study nature, the more I become impressed with ever-increasing force, that the contrivances and beautiful adaptations, slowly acquired through each part occasionally varying in a slight degree, but in many ways, with the preservation of those variations which were beneficial to the organism under complex and ever varying conditions of life, transcend in an incomparable manner the contrivances and adaptations which the most fertile imagination of man could invent."[CD]

In preparing the present summary of recent advances in this department of natural history, I have resorted freely to quotation, because of the obvious rule, that it is better for scientific interest, for proper understanding, and for regulation of all subsequent reasoning on the facts, that we have the observations presented as nearly as possible by those who made them, and that we have more general inferences in the very words of those whose minds have been filled and swayed by impressions made in the field of observation itself. In now proceeding to consider the bearing of these advances on religious thought, I shall keep as far as possible by the same rule, desiring that science may interpret itself, and translate its own special conclusions into their fit place within a scheme of the universe. And whatever there may be here of material for detailed inference, it will be taken by religious men as abundantly clear, that science in slowly unfolding to general view these secrets of nature, renders a lasting and most valuable service to religion. Our religious convictions and emotions rest on a wider intellectual basis according to the fulness with which we understand the marvels of adaptation and contrivance which lie covered from ordinary observation under the attractive surface of nature.

Altogether beyond such a general admission as this, however, it must be obvious that in the mass of deeply interesting material now before us, there lies a considerable number of truths needing to be gathered into generalized form, bearing upon the laws of nature applying to living organism. As records of details are extended before us, the marvels of structure are obvious. The multifarious contrivances become quite startling, until we are ready to lose our reckoning in the very multiplicity of facts narrated. In order to make sure of general result, we need to draw off somewhat from details,--to be content even to lose sight of many of them,--in order to gain a position, sufficiently removed for a sight of general relations. In attempting this it is clear that there are certain truths bearing on the preservation and development of species in the vegetable kingdom, and an analogous set of truths as to the animal kingdom, and above these, possibly still more important for general appreciation of the universe as a whole, a body of truth as to the relations of plants and animals.

As to the first of these, it seems obvious that within the single field of observation presented by orchids,--comparatively narrow, in view of the wide domain of the vegetable kingdom, and yet astonishingly extensive, on account of the richness of detail,--there is a large body of evidence to support the theory of origin of species by selection and adaptation. Whether all the orchideæ now found in existence have sprung from one order of plant, or from several, the testimony appears ample to support at least the following conclusion as presented in the words of Mr. Darwin, "that the now wonderfully changed structure of the flower is due to a long course of slow modification,--each modification having been preserved which was useful to the plant, during the incessant changes to which the organic and inorganic world has been exposed."[CE]

By a line of inference exactly similar, a like conclusion, must be reached as to insect life. For, important as the observations are, bearing on the transference of pollen from the place where it is generated to the place where it is wanted, we must notice that the whole work is done in consequence of search for honey by flies, moths, ants, wasps, and bees. It naturally follows that all these insects have been going through some measure of adaptation, as well as the plants. The same law must have been operating in their history while prosecuting the unceasing search for food. It may be exceedingly difficult to fill up the line of progress, or trace the causes in operation, which could favor the conclusion that all the insects named have sprung from a common stock. Still more perplexing might it be to maintain the argument that these very insects have sprung according to a sure law of descent, from vegetable life itself. But there is ample evidence to warrant the inference that in length of proboscis, formation of limbs, and other features in their structure, modifications have resulted from the struggle needful to reach the nectar secreted in the flowers.

But it is clearly impossible to stop here in our inferences. There is interdependence of lower and higher organisms, to which a distinct place needs to be assigned in our theory of the universe. Even if it be granted, as it readily will be by those who have studied the results of recent research, that there is a vast body of evidence to prove that there is development of species by adaptation and selection, it is equally evident that this is not the only law affecting the existence of different orders of organized beings. Just as clear as it is that pollen and seed are both required to provide for the continuance of plant life, so clear is it that plants are needed to support insects, and insects to propagate plants. Proceeding on the same lines of reasoning as have been already employed, we must inquire how this interdependence is to be accounted for under natural law? The struggle for existence is clearly performing an important part in the development of plants, and also of animals; and so long as we regard these two orders singly, it seems obvious how changes in structure may be accounted for; but observations have become so interlaced, that a new problem has been raised in connection with facts manifestly abating the struggle for existence. In view of this problem Dr. Hooker has said,--"The adjustment of the parts of the flower to the form and habits of the insect or bird, and of these to the flower, is so accurate, that it is in vain to speculate whether the plant was adapted to feed the animal, or the animal adapted to fertilize the plant."[CF] This suggestion of the needlessness of speculation is natural from a scientific point of view, and we may do well to remember the warnings against risks attending the search for final causes, which have been sounded from the days of Spinoza to the present time; but there is a problem here which science can not leave in abeyance. The facts are undoubted, and the natural causes must be sought. The parts of the flowers are adapted to the forms and habits of the insects; the insects are adapted to the work of fertilizing the plants; the question is, How are these two things secured? The inquiry which has awakened general interest as to the development of species in the history of distinct orders such as orchids, insects, pigeons, and dogs, must strive to complete its work, by pressing on to this more complicated question concerning the adaptation of distinct organisms to influence and aid each other in the work of development. In what way science may deal with this question, and how far it may be able to advance in the search for an answer, it may be difficult to decide. For it is much easier to indicate the logical necessity for an advance, than to say in what manner the advance is to be accomplished. The one is a simple question of logical requirement; the other must be a matter of continued observation, and scientific inference. Whether science may yet discover an answer; or whether it may prove true at this point, as at other points already mentioned, that science has here reached clear marks of its own limits, must be left to the future, to be determined by those devoted to scientific research. As long, however, as this question of interdependence remains without a scientific explanation, it must be obvious that there are important facts which seem to imply some modification of the theory of descent, or evolution of species by means of selection, under the severe struggle for existence. Or, to put it from another point of view, nature has marvellously provided for mitigation of the struggle for existence, by contrivances providing both for vegetable and animal life; therefore the theory of the origin and development of life which depends chiefly on the struggle for existence must be adjusted to allow for a theory of the effects arising from the natural provision for obviating the struggle, and providing for a large increase of life.

Quite beyond this, as a matter entirely distinct, is the question as to the primordial forms of existence in the history of plants and insects. As to this, science may be able to give very little testimony, as it is a question of the remote past, on which present facts may afford little evidence. Still, beyond these primordial forms, in a region which science can not enter, there lies the question of origin, of actual beginning, creation of life, as to the reality of which science can speak only indirectly by discovery of its own limits, in the terms of its _ultimatum_, nature has provided that such and such things shall be.

Before leaving the department of insect life, there is a collateral and complementary series of observations, bearing upon the nature and activity of ANTS, which deserves attention. The ants are a race of insects as diligently industrious as the bees, like them also fond of honey and of all sweet substances; but unlike them ready to devour other insects. Along with the industry of the bee, they have predatory tendencies, leading them into conflict with other races, or even involving different orders of their own race in warfare. It is a curious fact, in this connection, that many of the flowering plants have contrivances which guard them from the approach of ants. Creeping insects find the way barred against them while the flying insect at once and easily reaches the stores of honey, not knowing any thing of the difficulties in the path of the less favored rival. Spikes grow with their points in a downward direction, against which no creeping insect can make way; waxy or glutinous matter is spread over the leaves, which insects shun as a trap; and there are velvety flexible leaves from the edge of which the insect easily slips off. Special attention has been turned to this field of research by Kerner,[A] an interesting outline of the results of his observations being given by Sir John Lubbock.[CG] The conclusion reached as to the utility of these contrivances for exclusion of creeping insects, is that they perform an auxiliary part in the general plan for fertilization which has been described. To allow the store of honey to go to the ants would be merely to feed them without any equivalent advantage to the flowers. To diminish the supply in this way, might cause the bees to abandon many flowers, and so greatly diminish fertilization. This would ultimately lead to short supplies, and probable extinction of several orders of plants and animals, and accordingly these contrivances to hinder the access of ants, must be added to those for facilitating the approach of bees, and other flying insects, affording further evidence of the adjustment of rival interests involved in the relations of the vegetable and animal kingdoms. The serried spikes are a phalanx of bayonets planted for resistance of an advancing foe.

Contemplating now the ants as in some respects an excluded race, which with a large share of pugnacity can not find a basis of operations for contending against the bees, we have to turn attention briefly on their modes of life. The industry of the ant is proverbial, and can not fail to arrest the attention of any one who spends a few minutes before an ant-hill. But carefully recorded observations prove it to be much greater than could have been imagined. Sir John Lubbock has rendered special service here by carefully noting the time occupied, as well as the amount of work done, thus preserving a series of observations exceedingly suggestive in many ways, and having an important bearing on a considerable number of difficult questions connected with the relative powers of lower and higher orders of life. A similar service has been rendered in America in the work of the Rev. H. C. McCook of Philadelphia, on _The Natural History of the Agricultural Ant of Texas_,--a book recording careful and most important observations, adding much to the stores of knowledge concerning ants.[CH]

The work of the ants is directed mainly to the two great objects of animal life, procuring food, and caring for the young, to which falls to be added, the repelling of attacks upon their nests, or removal of any thing obnoxious. They destroy great numbers of smaller insects, bearing them to their nests for consumption, besides going off in search of honey which may be within reach, and not guarded with spikes. This mode of providing implies a very busy life, and they do not as a rule grudge work. Besides procuring supplies, however, there is a large amount of labor in the care bestowed upon their young. Without attempting to distinguish various orders, of which "more than seven hundred kinds are known,"[CI] a general description of their young will suffice. In the earliest stage of their existence, the larvæ are small conical shaped grubs, without power of movement. In this state they are fed, carried about from place to place as if their seniors were seeking change of air and temperature for them; and in process of these removals and arrangements, they are often grouped together in separate companies, and in exact order according to their size. In their next stage, they become pupæ, sometimes quite exposed, in other cases covered with a thin silken covering. From this, they pass into the mature state as perfect insects, and in process of this transition older ants render assistance by way of aiding the transition, "carefully unfolding their legs and smoothing out their wings."