Intelligence in Plants and Animals / Being a New Edition of the Author's Privately Issued "Soul and Immortality."

by Thomas G. Gentry

When a species, owing to highly favorable conditions, increases inordinately in numbers in a small tract of country, epidemics, especially in game animals, often occur, and here we have a limiting check independent of the Struggle for Existence. But some of these so-called epidemics appear to be due to parasitic worms, which have from some cause, possibly in part through ease of diffusion among the crowded animals, been disproportionately favored, and here comes in a sort of struggle between the parasite and its more illustrious prey.

But, on the other hand, as is frequently the case, a large stock of individuals of the same species, relatively to the number of its enemies, is absolutely essential to its preservation. We thus see how it is possible to raise with ease a plentiful supply of corn in our fields, because the seeds are greatly in excess of the number of birds which feed thereon. Nor can the birds, though blessed with a superabundance of food at this one season, increase in number in proportion to the supply of seed, as their numbers are checked during the winter. Any one, however, who has made the experiment, knows how troublesome it is to get seed from a few wheat or other such plants sown broad-cast in a garden. Some singular facts in nature, such as that of very rare plants being sometimes extremely abundant in the few spots where they do occur, and that of some social plants being social, or abounding in individuals, even on the extreme confines of their range, are readily explainable by this view of the necessity of a large stock of the same species for its preservation, for in such cases we may believe that a plant could only exist where the conditions of its life were so favorable that many could exist together and thus save the species from extinction.

Complex and varied are the checks and relations between organic beings which have to struggle together in the same country. In the case of every species, many different checks, some very complicated and unintelligible to man at present, acting at different periods of life, and during different seasons or years, come into play, some one check or some few being generally the most powerful, but all concurring in determining the average number or even the existence of the species. Widely-different checks sometimes act on the same species in different districts. Looking at the plants and bushes that clothe an entangled bank, we are tempted to ascribe their proportional numbers and kinds to what we call chance. But this is a very false view to take of the matter. Chance has no part in such things. They follow in obedience to laws of which we know comparatively little. When an American forest is cut down a very different vegetation springs up. Ancient Indian ruins have been observed in the southern parts of the United States, which must in former times have been cleared of trees, but which now display the same beautiful diversity and proportion of kinds as are now found in the surrounding virgin forest. What a struggle must have gone on during long centuries between the several kinds of trees, each annually scattering its seeds by the thousand, and what a war between insect and insect, and between insects, snails and other animals with birds and beasts of prey, all striving to increase, all feeding on each other, or on the trees, their seeds and their seedlings, or on the other plants which once clothed the soil, and thus checked the growth of the trees! It is easier to account for the fall of an apple from a tree, or the descent of a stone to the earth when hurled into the air, than to account for the action and reaction of the innumerable plants and animals that have determined in the course of untold centuries the proportional numbers and kinds of trees that are now found growing on these old Indian ruins. But the struggle will almost invariably be the severest between individuals of the same species, for they frequent the same districts, require the same food and are exposed to the same dangers. In the case of varieties of the same species, the struggle will generally be almost equally severe. If several varieties of wheat be sown together, and the mixed seed be re-sown, some of the varieties which best suit the soil or climate, or are naturally the most fertile, will beat the others and so yield more seed, and will consequently in a few years supplant the others. Such extremely-close varieties as the variously-colored sweet-peas must be separately harvested each year, and the seed mixed in due proportion, or the weaker kinds will steadily decrease in number and disappear. So, again, with the varieties of sheep. Certain mountain-varieties will starve out other mountain-varieties, so that they cannot be kept together. Similar results have followed from keeping together different varieties of the medicinal leech. In view of all that has been said, it is questionable whether the varieties of any of our domestic plants and animals have so exactly the same vigor, constitution and habits that the original proportions of a mixed stock could be kept up for a half-dozen generations if they were permitted to struggle together like beings in a state of nature, if the seed or young were not annually assorted.

Species of the same genus having usually, though not invariably, much similarity in habits and constitution, and always in structure, the struggle will be more severe between species of the same genus, where they come into competition with each other, than between species of distinct genera. One species of swallow has caused in certain parts of the United States the decrease of another species, just as the missel-thrush in parts of Scotland has caused the decrease of the song-thrush. The small Asiatic cockroach has everywhere in Russia driven before it its great congener, and the imported European hive-bee is rapidly exterminating in Australia the small, stingless bee, indigenous to the country. Hundreds of such cases might be cited, but we forbear. We can clearly see why the competition should be most severe between allied forms, which fill nearly the same place in the economy of nature; but it is perhaps not possible to individualize a case and say with preciseness why such species has been victorious over another in the battle of life. That the structure of every organic being is related, in the most essential yet often hidden manner to that of all the other organisms with which it comes into competition for food or residence, or from which it has to escape, or on which it preys, is a corollary of the highest importance deducible from the foregoing remarks. Very obvious is this in the structure of the teeth and talons of the tiger, and in that of the legs and claws of the parasite which clings to the hair on the tiger’s body. But in the beautifully-plumed seed of the dandelion and the flattened and fringed legs of the water-beetle the relation seems at first restricted to the elements of air and water, yet the advantage of plumed seeds undoubtedly stands in the most intimate relation to the land, being already densely clothed with other plants, so that the seeds may be widely diffused and fall on unoccupied ground, while in the water-beetle, the structure of its legs, so admirably adapted for diving, allows it to compete with other aquatic insects, to hunt for its own prey and to escape destruction by other predaceous animals. All organic beings, it will thus be seen, are not only striving to increase in numbers, but are called upon some time in their lives to struggle for existence or to suffer serious if not utter destruction. When we reflect on this struggle, we can console ourselves with the full belief that this war of nature is not incessant, that no fear is felt, that death is generally sudden, and that the vigorous, healthy and happy survive and multiply.

Seeing what a potent influence the principle of Selection has in the hands of man, in regard to variation, can it be applied in nature? We can see that it can act most effectually. But in our domestic productions the variability is not directly produced by man, for he can neither originate varieties nor prevent their occurrence. All he can do is to preserve and accumulate such as do occur. Unintentionally he exposes organic beings to new and changing conditions of life, for under domestication, plant and animal organizations become in some degree plastic, and variability ensues. Similar changes, however, do occur in nature. When it is borne in mind how infinitely complex and close-fitting are the mutual relations of all organic beings to each other, and to their environment, and consequently what infinitely-varied diversities of structure may be of advantage to each being under altered conditions, can it then be thought improbable, seeing that variations useful to man have undoubtedly occurred, that other variations useful in some way to each being in the great and complex battle of life should sometimes occur in the course of tens of thousands of generations? If such do occur, can we doubt, when it is remembered that many more individuals are born than can possibly survive, that individuals possessing any advantage, no matter how slight, over their fellows would have the best chance of surviving and of procreating their kind? Any variation, on the other hand, we may feel sure if in the least degree injurious would be rigidly destroyed. This preservation of useful and favorable variations, and the destruction of those that are injurious, is called Natural Selection, or the Survival of the Fittest. Variations neither advantageous nor deleterious would not be affected by Natural Selection, and would be left either a fluctuating element, as seen in certain polymorphic species, or would alternately become fixed, owing to the nature both of the organism and its conditions.

We shall best understand the probable cause of Natural Selection by taking a country undergoing some physical change, as of climate for example. The proportional number of its inhabitants would almost immediately undergo a change, and some of its species might become extinct. From the complex and very intimate manner in which the inhabitants of each country are bound together, we may conclude that any change in the numerical proportion of some of its inhabitants, independently of the change of climate itself, would seriously affect the others. Were the country open on its borders, new forms would certainly immigrate, and this, too, would often seriously disturb the relations of some of its former inhabitants. In the case, however, of an island, or a country hemmed in by barriers, into which new and better-adapted forms could not readily enter, we would then meet with places in the economy of nature which would assuredly be better filled up, if some of the original occupants were in some manner modified, for had the area been open to immigration, these same places would have been seized by intruders. Thus, slight modifications, which any way favored the individuals of a species, would by better adapting them to changed conditions tend to become preserved, and Natural Selection would there have free scope for the work of improvement. Changes in the conditions of life cause or excite a tendency to vary. In the foregoing case the conditions are supposed to have changed, and this would manifestly be favorable, by giving a better chance of profitable variations occurring, to Natural Selection, for unless such do occur, Natural Selection can do nothing. As man, by adding up in any given direction individual differences, can certainly produce a great result with his domestic animals and plants, so could Natural Selection, but far more easily from having an incomparably longer time for its action. No great physical change, as of climate, nor any unusual degree of isolation to check immigration, is actually necessary, it would seem, to produce new and unoccupied places for Natural Selection to fill up by modifying and improving some of the varying inhabitants, for as all the inhabitants of a country are struggling together with nicely-balanced forces, extremely-slight modifications in the structure or habits of one species would often give it an advantage over others; and still further modifications, so long as the species continued under the same conditions of life and profited by similar means of subsistence and defence, would often still further augment the advantage. No country can be mentioned whose native inhabitants are now so perfectly adapted to each other and to their environment that none could be better adapted and improved, for in all countries the natives have been so far conquered by naturalized productions as to have allowed them to take firm possession of the land. And as foreigners have thus in every country beaten some of the natives, it may be safely concluded that the latter might have been modified with profit so as to have better resisted the intruders.

A man by his methodical and unconscious means of selection can produce and has produced great results. What may not Natural Selection effect? Man can only operate on external and visible characters, but nature cares nothing for appearances, except in so far as they are beneficial to any being. She can act on every internal organ, on every shade of constitutional difference and, in fine, on the entire machinery of life. Man selects exclusively for his own advantage, but nature solely for that of the being she tends, and under her judicious selection the slightest difference of structure or constitution may well turn the nicely-balanced scale in the Struggle for Existence, and thus be preserved. As fleeting as are the wishes and efforts of man, and as short as is his earthly career, so poor, therefore, must be the results which he accomplishes when compared with those accumulated by nature during whole geological periods. Is it a wonder, then, that her productions should be far truer in character than man’s, and that they should be infinitely better adapted to the most complex conditions of life and should bear the stamp of far higher workmanship? Metaphorically speaking, Natural Selection may be said to be daily and hourly scrutinizing, throughout the world, the slightest variations, rejecting the bad, preserving and adding up the good, and silently and insensibly working, whenever and wherever opportunities occur, at the betterment of each organic being in relation to its organic and inorganic conditions of life. So slow is her work that we see nothing of the changes in progress, and only when the hand of time has marked the lapse of ages do we perceive that changes have been produced; but then so imperfect is our view into long-past geological periods, that we see only that the forms of life are now different from what they formerly were. That any great amount of modification in any point should be effected, a variety once formed must again, perhaps after a long interval of time, present individual differences of the same favorable character, and these must again be preserved, and so onward step by step. As individual differences of all kinds perpetually recur, this can hardly be considered as an unwarrantable assumption. Judged by the extent the hypothesis accords with and explains the general phenomena of nature, notwithstanding the ordinary belief that the amount of possible variation is a strictly-limited quantity, we are justified, it seems to us, in assuming that all this has actually taken place. But in looking at many small points of difference between species, which in our ignorance seem quite unimportant, we must not lose sight of the facts that climate, food and modes of life may have produced some direct effect, and also of the truth that, owing to the Law of Correlation, when one part varies, and the variations are accumulated through the Survival of the Fittest, other modifications often of the most unlooked-for nature will ensue.

As under domestication these variations are known to appear at a particular period of life, and tend to reappear in the offspring at the same period, so, in a state of nature, it is reasonable to infer that Natural Selection will be enabled to act on and modify organic beings at any age, by the accumulation of variations useful at that age, and by their inheritance at a corresponding age. Thus, if it be profitable to a plant to have its seeds more and more widely disseminated by the wind, there can be no greater difficulty in conceiving this to be effected through Natural Selection than in conceiving the increasing and improving of the down in the pods on his cotton-trees by a wise selection upon the part of a cotton-planter. Natural Selection may modify and adapt the larva of an insect to a score of contingencies, wholly different from those which affect the mature insect, and these modifications through Correlation may work changes in the structure of the adult. On the other hand, modifications of the adult may affect the structure of the larva, but in all such cases Natural Selection will insure that these changes shall not be injurious, for, if they were so, the extinction of the species would be the inevitable result. Thousands of instances might be given to show the influence which Natural Selection, or Sexual Selection, which is only a less vigorous phase of the former, has had all through the ages in the adaptation of life to the places in nature which it was intended to occupy in pursuance of the plan formulated by the Great Originator and Designer of the Universe.

Despite the imperfection of the geological record, which has been urged as a serious objection to the theory of descent with modification, sensible, intelligent, educated men no longer doubt that species have all changed, and that they have changed in the way required, for they have changed slowly and in a graduated manner. This is clearly seen in the fossil remains from consecutive formations being invariably much more closely allied to each other than are those from widely-separated formations. It is true geological research does not yield those infinitely fine gradations between past and present species which the theory of Natural Selection requires, but when it is remembered that only a small portion of the world has been geologically explored; that only organic beings of certain classes, at least in any great number, can be preserved in a fossil condition; that many species when once formed never undergo any further change, but become extinct without leaving any modified descendants; that dominant and widely-ranging species vary the most and the most frequently, and that varieties are often at first only local, it is not at all surprising that the discovery of intermediate links to any considerable extent should not have been made. Local varieties, as is well known, will not diffuse themselves into other and distant localities until they have become very much modified and improved, and when they have thus diffused themselves, and are discovered in a geological formation, they will appear as if suddenly created there, and will simply be ranked as new species. Besides, formations have often been intermittent in their accumulation, and their duration has probably been shorter than the average duration of specific forms. And as successive formations in most cases are separated from each other by blank intervals of time of considerable length, and as fossiliferous formations thick enough to withstand future degradation can as a general rule be accumulated only where much sediment is laid down in the subsiding bed of the ocean, it follows that during the alternate periods of elevation and of stationary level the record will generally be blank or devoid of fossil remains. During these latter periods there will doubtless be more variability in the forms of life, and during the periods of subsidence a greater amount of extinction. Now, as geology plainly declares that each land has undergone great physical changes, we have a right to expect that organic beings have varied under nature in the same manner as they have varied under domestication, and such have scientific study and research found to be the case. And if there has been any variability under nature, such a fact would seem unaccountable unless Natural Selection, or the Survival of the Fittest, did not come into play. Upon the view that variations have occurred in nature and have been preserved and accumulated by Natural Selection, and not in the ordinary view of independent creation, we can understand why the specific characters, or those by which the species of the same genus differ from each other, should be more variable than the generic characters in which they all agree. Inexplicable as is the occasional appearance of stripes on the shoulders and legs of the different equine species and their hybrids on the theory of creation, yet how simply is the fact explained if we believe that they are all descended from a striped progenitor just as the different domestic breeds of pigeons are descended from the blue and barred rock-pigeons. Why, for example, should the color of a flower be more likely to vary in any one species of a genus, if the other species, supposed to have been created independently, have differently-colored flowers, than if all the species of the genus have the same colored flowers? On the theory that species are only well-marked varieties, of which the characters have become in a high degree permanent, the fact is intelligible, for they have already varied in certain characters since they branched off from a common progenitor, and by these characters they have come to be specifically distinct from each other. Therefore, these same characters would be more likely again to vary than the generic characters which have been inherited without change for an enormous period of time.

Upon the theory of Natural Selection, or the Survival of the Fittest, with its contingencies of extinction and divergence of character, we can see how it is that all past and present organic beings can be arranged within a few classes, in groups subordinate to groups, and with the extinct groups often falling in between the recent groups. We can see how it is that the mutual affinities of the forms within each class are so complex and diversified, and only adaptive characters, though of superior importance to the beings, are of scarcely any significance in classification, while those derived from rudimentary parts, though of no recognized service, are often of high classificatory value, and only embryological characters are frequently the most valuable of all. The real affinities of all organisms, in contradistinction to their adaptive likenesses, are due to inheritance or community of descent. Hence, a natural system of classification is a genealogical arrangement, with the acquired grades of difference, denoted by varieties, species, genera, families, etc., and their lines of descent have to be discovered by the most permanent characters, whatever they may be and how little of vital importance they may possess.