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

by Thomas G. Gentry

Man is in reality but on the threshold of civilization. Far from showing any indication of having reached the end, the tendency to improvement seems laterally to have proceeded with augmented impetus and accelerated rapidity. There is no reason to suppose that it must now cease. Man has not attained the limits of intellectual development, nor exhausted the infinite capabilities of nature. There are many things not yet dreamt of in our philosophy which science must reveal, many discoveries yet to be made which will confer upon the human race advantages which as yet, perhaps, we are not in a condition to grasp and appreciate. We seem, when we compare our present knowledge with the great ocean of truth that lies all undiscovered before us, like little children playing on the sea-shore, and picking up a smoother pebble and prettier shell than any they had met with before. Thus, it is obvious, that our most sanguine hopes for the future are justified by the entire experience of the past. It is surely unreasonable to presume that a process which has been going on for so many thousand years should have now suddenly ceased; and he must indeed be blind who thinks that our civilization is unsusceptible of improvement, or that we ourselves are in the highest state possible for man to attain. Theory, as well as experience, forces the same conclusion upon us. That principle of Natural Selection, which in animals affects the body and seems to have little influence on the mind, in man affects the mind and has little influence on the body. In the former it leads mainly to the preservation of life, and in the latter to the improvement of the mind, and consequently to the increase of happiness. It ensures, in the words of Spencer, “a constant progress towards a higher skill, intelligence, and self-regulation—a better coördination of actions—a more complete life.” Nearly all the evils under which we suffer, it will be conceded, may be attributed either to ignorance or sin. That ignorance will be diminished by the progress of science is, of course, self-evident; and that the same will be the case with sin, seems little less so. Thus, then, do both science and theory point to the same conclusion. That which poets hardly dared to hope for, the future happiness of our race, science boldly predicts. Even in our own time we trust to see some wonderful improvement. But the unselfish mind, however, will find its highest gratification in the belief that, whatever may be the case with ourselves, our descendants will understand many things which are mysterious to us now, will better appreciate the beautiful world in which we live, avoid much of the suffering to which we are subject, enjoy many blessings of which we are not yet worthy, and escape many of those temptations which we deplore but cannot wholly resist.

We have thus seen that all life has been progressive. There has been through the ages a steadily growing upward tendency to higher life. But the changes have mainly been in the line of physical form and structure. And such, too, had been the case with man, until his social, intellectual and moral faculties had begun to assert themselves, when his body ceased in a great measure to be acted upon by physical laws, and development began to manifest itself in a higher type of mental organization. From the low, simple, childlike mind of palæolithic man has come that wonderful intellect which now characterizes the Germanic races, and which is destined to make itself felt in its contact with all the earth. Those peoples that are able to embrace the new civilization brought to their doors, so to speak, will survive, while the others, unable to adapt themselves thereto, like the Tasmanian, will succumb in the struggle with a superior being and go to the wall. Animals and plants will be brought into new relations and new conditions, and such as can meet the new requirements will, as certain species have done before, endure. They will, in other words, have partaken of an enlightened civilization. Thus things will go on until all life, vegetal and animal, will be brought under the controlling and elevating influence of man, and then will be inaugurated on earth that condition when the lion and the kid shall lie down together, and a little child shall be found in their midst. Nothing harmful will anywhere exist. Heaven will then have been brought down to earth, and peace and harmony will universally prevail. Then will have come the complete triumph of mind over body. All growth and development of the reformed and regenerated earth-man will be in the direction of mind, and his accomplishments will he share with the inferior subjects of his peaceful and happy domain. Progression, however, will not cease, but will go on steadily advancing as the years increase. And if there is a life beyond the earth-life, then the intellect or mind, or soul if you please, shall, in some form or other, exist therein, and reach up into higher and yet higher growth and development.

SURVIVAL OF THE FITTEST.

Among organic beings in a state of nature there is some individual variability. This is an admission about which there can be no dispute. But the mere existence of individual variability and of a few well-marked varieties, though necessary as the foundation for the work, assists us but little in understanding how species originate in nature. Those exquisite adaptations of one part of the organization to another part, and to the conditions of life, and of one organic being to another being, which we know to exist, seem as mysteries. We see them in the humblest parasite that clings to the hairs of a quadruped or the feathers of a bird, in the structure of the beetle that dives through the water, and in the plumed seed that is wafted by the gentlest breeze. In short, we see beautiful adaptations everywhere and in every part of the organic world. And yet, how few have paused while admiring these beautiful and wonderful co-adaptations to ask themselves the question: How have these been perfected?

If the existence of any well-marked varieties be admitted, how is it that these varieties, which may be denominated incipient species, become ultimately converted into good and distinct species, which in the generality of cases obviously differ from each in a greater degree than do the varieties of the same species? How do these groups of species, which constitute what are authoritatively called genera, and which differ from each other more than do the species of the same genus, arise? All these results, as will presently be seen, follow from the Struggle for Existence. Owing to this struggle, all variations, no matter how slight they may be, or from what cause soever they may proceed, will, if they be in any degree profitable to the individuals of a species in their infinitely complex relations to other organic beings and their physical conditions of life, unavoidably conduce to the preservation of such individuals, and generally be inherited by the offspring. The offspring, too, will thus have a better chance of surviving, for, of the many individuals of a species that are periodically born, but a very small number can survive. That principle, by which each slight variation, if useful to the individual, is preserved, has been termed Natural Selection by Darwin, in order to distinguish it from the selection which is exercised by man over the plants and animals which he has brought under subjection for his own wants. But the expression—Survival of the Fittest—so frequently used by Spencer, is more accurate, and sometimes equally convenient. Man can certainly produce great results by this power, and can adapt, through the accumulation of slight but useful variations given to him by the hand of nature, organic beings to his own uses. But Natural Selection, as is well known, is a power incessantly ready for action, and is as infinitely superior to man’s feeble efforts as the works of nature are to those of art.

All organic beings are exposed to severe competition. Nothing is easier than to admit in words the truth of the universal struggle for life, or more difficult than constantly to bear this conclusion, which has been reached through the investigations and researches of De Candolle, Lyell, Herbert, Darwin and others, in mind. Unless, however, it be thoroughly ingrained in the mind, the whole economy of nature, with every fact on distribution, rarity, abundance, extinction and variation, will be but dimly perceived or quite misunderstood. We behold the face of nature radiant with gladness, and food everywhere in excessive abundance, but we do not see that the birds which are happily singing round us mostly live on insects or seeds, and are thus constantly destroying life, or we fail to remember how largely these songsters, or their eggs, or their nestlings, are destroyed by birds and beasts of prey. Yes, we do not always bear in mind that, though food may now be superabundant, it is not so at all seasons of each recurring year. The term, Struggle for Existence, must be used in a large and metaphorical sense. It must be construed to include the dependence of one being on another, and also not only the life of the individual but also its success in leaving offspring. Two carnivores, in a time of scarcity of food, may be truly said to struggle with each other for maintenance of life. But a plant on the edge of a desert is said to struggle for life against the drought, though, properly speaking, it is dependent for its existence upon the moisture. A plant, however, that annually produces many thousand seeds of which on an average only one comes to maturity, may in a much truer sense be said to struggle with the plants of the same and other kinds which already invest the ground. While the mistletoe is dependent on the apple and some other trees, yet it cannot be said, unless in a far-fetched sense, to struggle with these trees, for, if too many of these parasites are found upon the same tree, it will certainly languish and die. Several seedling mistletoes, however, growing close together upon the same branch, may more truly be said to struggle with each other.

From the high rate at which all organic beings tend to increase, there must inevitably follow a Struggle for Existence. Every being which, during its natural lifetime, produces several eggs or seeds, must necessarily suffer destruction during some part of that period, and during some season or occasional year, otherwise, on the principle of Geometrical Increase, its numbers would become so inordinately excessive that no country would be able to support its product. Therefore, as more individuals are produced than can possibly survive, there must be in every case a Struggle for Existence, either one individual struggling with another of the same kind, or with individuals of distinct kinds or species, or with the conditions of the environment. This is the doctrine of Malthus applied with manifold force to the entire vegetable and animal kingdoms. Although some species may be now increasing at a very high rate in numbers, yet all cannot do so, for the earth would not be able to contain them. Slow-breeding man has doubled in twenty-five years, and should he go on at this rate for a few thousand years, there would literally not be standing room for his progeny. It has been calculated that, if an annual plant produced only two seeds, and their seedlings next year produced two, and the same rate of increase was kept up for twenty years, there would be a million of plants as the result. Even the elephant, which is reckoned the slowest breeder of all known animals, would after a period of from seven hundred and forty to seven hundred and fifty years leave nearly nineteen million elephants as descendants from the first pair.

Much better evidence than mere theoretical calculations are not wanting on this subject. Instances are recorded of the astonishingly rapid increase of various animals in a state of nature, when conditions have been favorable to them, during two or three succeeding seasons. More striking, however, is the evidence from domestic animals that have run wild in several parts of the world. Were not the statements of the rate of increase of cattle and horses in South America, and latterly in Australia, where millions now abound, well authenticated, they would have been incredible. Cases could be mentioned of introduced plants that have become quite common throughout entire islands in a period of less than twelve years. Several of these plants, the cardoon and a rare thistle, which were introduced from Europe, clothe square leagues of the surface of the wide plains of the La Plata almost to the exclusion of all other plants; and there are plants which now range in India, from Cape Comorin to the Himalaya, which have been imported from America since its discovery. In all such cases, and endless instances could be adduced, no intelligent person supposes that their fertility has been increased in any sensible degree by change of habitat, the obvious explanation being that the conditions of environment have been very favorable, and that there has consequently been less destruction of old and young, and that nearly all the latter have been enabled to breed. The extraordinarily rapid increase and wide diffusion of naturalized productions in new homes, a result which never fails to evoke surprise, is only to be explained on the principle of the Geometrical Ratio of Increase. As in nature almost every plant produces seed, and there are very few animals that do not annually pair, therefore we can confidently assert that all plants and animals are tending to increase in a geometrical ratio; that all would most rapidly stock every station in which they could in any way exist, and that the tendency to increase must be checked by destruction at some period of life. Among our larger domestic animals we see no great destruction falling on them. We forget that thousands are annually slaughtered for food, and that in a natural state an equal number would have to be disposed of in some way or other. Between organisms which annually produce seeds or eggs by the thousands, and those which produce extremely few, the only difference is that the slow breeders would require a few more years to people, under favorable conditions, a whole district, let it be ever so large. But a couple of eggs are laid by the condor, while the ostrich lays a score. Yet in the same country the condor may be the more abundant of the two. The Fulmer petrel lays but a single egg, yet it is believed to be the most numerous bird in the world. A large number of eggs is of some importance to those species which depend upon a rapidly-fluctuating quantity of food, for it permits them to increase rapidly in number; but the real importance of a large number of eggs or seeds is to make up for the great destruction that goes on at some period of life, and this period in the vast majority of cases is an early one. If an animal can in any way protect its own eggs or young, a small number may be produced, and the average stock be kept up; but if many eggs or young are destroyed, then many must be produced or the species will become extinct. Therefore, the average number of any animal or plant depends, though only indirectly, upon the number of its eggs or seeds. We should never forget, in taking a survey of nature, that every single organic being around us may be said to be striving to the utmost to augment its members; that each lives by a struggle at some period of its existence, and that heavy destruction falls either on the young or old during each generation or at recurrent intervals. Let any check be lightened, or the destruction be mitigated ever so little, and the number of the species will almost instantaneously increase to any extent.

But of the nature of the checks to increase we know little, although this subject has been very ably treated by writers of eminence. Eggs or very young animals seem generally to suffer the most, but this is not invariably the case. While there is a vast destruction of the seeds of plants, but it is the seedlings which are believed to suffer the greatest, from germinating in ground already thickly stocked with other plants, and from being destroyed in large numbers by various enemies. The amount of food for each species of course determines the extreme limit to which each can increase, but very often it is not the obtaining of food, but the serving as prey to other animals which fixes the average number of a species. Thus there seems to be little doubt that the stock of partridges, grouse and hares on any large estate depends mainly on the destruction of vermin. Were not a single head of game shot during the next twenty years in England, says Darwin in substance, and no vermin were at the same time destroyed, there would in all probability be less game than at present exists, although hundreds of thousands of game animals are now annually killed for the market. In some cases, on the other hand, as in the case of the elephant, none are destroyed by beasts of prey, for even the tiger in India, bold and venturesome as he is known to be, rarely dares to attack a young elephant protected by its mother. Climate, also, plays an important part in determining the average number of a species, and periodical seasons of extreme cold or drought are seemingly the most effective checks of all. The action of climate appears at first sight to be altogether independent of the Struggle for Existence; but in so far as it chiefly acts in the reduction of food, it brings on the most severe struggle between the individuals, whether of the same or different species, which subsist on the same kind of fare. Even when climate, extreme cold for example, acts directly, it will be the least vigorous animals, or those which have been the poorest fed through the advancing winter, that will suffer the greatest. This will be most readily seen from what we shall now relate. When we travel from south to north, or from a damp region to a dry, we invariably see some species getting rarer and rarer by degrees, and finally disappearing. Change of climate being conspicuous, we are inclined to ascribe the entire effect to its direct action, but this is a false interpretation of the phenomenon, for we fail to remember that each species, even where it most prevails, is constantly suffering enormous destruction at some period of its existence, from enemies or competitors for the same station and food; and if these enemies or competitors be the least favored by any slight change of climate, they will necessarily increase in numbers, while the other species, each area being already stocked with inhabitants, will correspondingly decrease. And when we travel southward and see a species decreasing in numbers, we may feel reasonably sure that the cause lies quite as much in other species being favored as in this being hurt. So it is when we travel northward, though in a less degree. When we go northward, or when we ascend a mountain, we far oftener meet with stunted forms, due to the directly injurious action of climate, than we do when we go southward or descend a mountain. When, however, we reach the Arctic regions, or explore snow-capped summits, or absolute deserts, we perceive the struggle for life to be almost exclusively with the elements.

That climate operates mainly, but indirectly, in favoring other species, may be clearly seen in the prodigious numbers of garden plants that can thoroughly well endure our climate, but which can never become naturalized, inasmuch as they cannot compete with native vegetation nor resist destruction by native animals.