The Outline of Science Part 28

Their wings have been turned into flippers for swimming in the sea and tobogganing on snow. The penguins come back over hundreds of miles of trackless waste to their birthplace, where they breed. When they reach the Antarctic sh.o.r.e they walk with determination to a suitable site, often at the top of a steep cliff. Some species waddle 130 steps per minute, 6 inches per step, two-thirds of a mile per hour.]

The Mind of a Minnow

To find solid ground on which to base an appreciation of the behaviour of fishes, it is necessary to experiment, and we may refer to Miss Gertrude White's interesting work on American minnows and sticklebacks.

After the fishes had become quite at home in their artificial surroundings, their lessons began. Cloth packets, one of which contained meat and the other cotton, were suspended at opposite ends of the aquarium. The mud-minnows did not show that they perceived either packet, though they swam close by them; the sticklebacks were intrigued at once. Those that went towards the packet containing meat darted furiously upon it and pulled at it with great excitement. Those that went towards the cotton packet turned sharply away when they were within about two inches off. They then perceived what those at the other end were after and joined them--a common habit amongst fishes. Although the minnows were not interested in the tiny "bags of mystery," they were even more alert than the sticklebacks in perceiving moving objects in or on the water, and there is no doubt that both these shallow-water species discover their food largely by sense of sight.

The next set of lessons had to do with colour-a.s.sociations. The fishes were fed on minced snail, chopped earthworm, fragments of liver, and the like, and the food was given to them from the end of forceps held above the surface of the water, so that the fishes could not be influenced by smell. They had to leap out of the water to take the food from the forceps. Discs of coloured cardboard were slipped over the end of the forceps, so that what the fishes saw was a morsel of food in the centre of a coloured disc. After a week or so of preliminary training, they were so well accustomed to the coloured discs that the presentation of one served as a signal for the fishes to dart to the surface and spring out of the water. When baits of paper were subst.i.tuted for the food, the fishes continued to jump at the discs. When, however, a blue disc was persistently used for the paper bait and a red disc for the real food, or _vice versa_, some of the minnows learned to discriminate infallibly between shadow and substance, both when these were presented alternately and when they were presented simultaneously. This is not far from the dawn of mind.

In the course of a few lessons, both minnows and sticklebacks learned to a.s.sociate particular colours with food, and other a.s.sociations were also formed. A kind of larva that a minnow could make nothing of after repeated trials was subsequently ignored. The approach of the experimenter or anyone else soon began to serve as a food-signal. There can be no doubt that in the ordinary life of fishes there is a process of forming useful a.s.sociations and suppressing useless responses. Given an inborn repertory of profitable movements that require no training, given the power of forming a.s.sociations such as those we have ill.u.s.trated, and given a considerable degree of sensory alertness along certain lines, fishes do not require much more. And in truth they have not got it. Moving with great freedom in three dimensions in a medium that supports them and is very uniform and constant, able in most cases to get plenty of food without fatiguing exertions and to dispense with it for considerable periods if it is scarce, multiplying usually in great abundance so that the huge infantile mortality hardly counts, rarely dying a natural death but usually coming with their strength unabated to a violent end, fishes hold their own in the struggle for existence without much in the way of mental endowment. Their brain has more to do with motion than with mentality, and they have remained at a low psychical level.

Yet just as we should greatly misjudge our own race if we confined our attention to everyday routine, so in our total, as distinguished from our average, estimate of fishes, we must remember the salmon surmounting the falls, the wary trout eluding the angler's skill, the common mud-skipper (Periophthalmus) of many tropical sh.o.r.es which climbs on the rocks and the roots of the mangrove-trees, or actively hunts small sh.o.r.e-animals. We must remember the adventurous life-history of the eel and the quaint ways in which some fishes, males especially, look after their family. The male sea-horse puts the eggs in his breast-pocket; the male Kurtus carries them on the top of his head; the c.o.c.k-paidle or lumpsucker guards them and aerates them in a corner of a sh.o.r.e-pool.

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The Mind of Amphibians

Towards the end of the age of the Old Red Sandstone or Devonian, a great step in evolution was taken--the emergence of Amphibians. The earliest representatives had fish-like characters even more marked than those which may be discerned in the tadpoles of our frogs and toads, and there is no doubt that amphibians sprang from a fish stock. But they made great strides, a.s.sociated in part with their attempts to get out of the water on to dry land. From fossil forms we cannot say much in regard to soft parts; but if we consider the living representatives of the cla.s.s, we may credit amphibians with such important acquisitions as fingers and toes, a three-chambered heart, true ventral lungs, a drum to the ear, a mobile tongue, and vocal cords. When animals began to be able to grasp an object and when they began to be able to utter sufficient sounds, two new doors were opened. Apart from insects, whose instrumental music had probably begun before the end of the Devonian age, amphibians were the first animals to have a voice. The primary meaning of this voice was doubtless, as it is to-day in our frogs, a s.e.x-call; but it was the beginning of what was destined to play a very important part in the evolution of the mind. In the course of ages the significance of the voice broadened out; it became a parental call; it became an infant's cry. Broadening still, it became a very useful means of recognition among kindred, especially in the dark and in the intricacies of the forest. Ages pa.s.sed, and the voice rose on another turn of the evolutionary spiral to be expressive of particular emotions beyond the immediate circle of s.e.x--emotions of joy and of fear, of jealousy and of contentment. Finally, we judge, the animal--perhaps the bird was first--began to give utterance to particular "words," indicative not merely of emotions, but of particular things with an emotional halo, such as "food," "enemy," "home." Long afterwards, words became _in man_ the medium of reasoned discourse. Sentences were made and judgments expressed. But was not the beginning in the croaking of Amphibia?

Senses of Amphibians

Frogs have good eyes, and the toad's eyes are "jewels." There is evidence of precise vision in the neat way in which a frog catches a fly, flicking out its tongue, which is fixed in front and loose behind.

There is also experimental proof that a frog discriminates between red and blue, or between red and white, and an interesting point is that while our skin is sensitive to heat rays but not to light, the skin of the frog answers back to light rays as well. Professor Yerkes experimented with a frog which had to go through a simple labyrinth if it wished to reach a tank of water. At the first alternative between two paths, a red card was placed on the wrong side and a white one on the other. When the frog had learned to take the correct path, marked by the white card, Prof. Yerkes changed the cards. The confusion of the frog showed how thoroughly it had learned its lesson.

We know very little in regard to sense of smell or taste in amphibians; but the sense of hearing is well developed, more developed than might be inferred from the indifference that frogs show to almost all sounds except the croaking of their kindred and splashes in the water.

The toad looks almost sagacious when it is climbing up a bank, and some of the tree-frogs are very alert; but there is very little that we dare say about the amphibian mind. We have mentioned that frogs may learn the secret of a simple maze, and toads sometimes make for a particular sp.a.w.ning-pond from a considerable distance. But an examination of their brains, occupying a relatively small part of the broad, flat skull, warns us not to expect much intelligence. On the other hand, when we take frogs along a line that is very vital to them, namely, the discrimination of palatable and unpalatable insects, we find, by experiment, that they are quick to learn and that they remember their lessons for many days. Frogs sometimes deposit their eggs in very unsuitable pools of water; but perhaps that is not quite so stupid as it looks. The egg-laying is a matter that has been, as it were, handed over to instinctive registration.

[Ill.u.s.tration: _Photo: W. S. Berridge._

HARPY-EAGLE

"Clean and dainty and proud as a Spanish Don."

It is an arboreal and cliff-loving bird, feeding chiefly on mammals, very fierce and strong. The under parts are mostly white, with a greyish zone on the chest. The upper parts are blackish-grey. The harpy occurs from Mexico to Paraguay and Bolivia.]

[Ill.u.s.tration: _Photo: W. S. Berridge, F.Z.S._

THE DINGO OR WILD DOG OF AUSTRALIA, PERHAPS AN INDIGENOUS WILD SPECIES, PERHAPS A DOMESTICATED DOG THAT HAS GONE WILD OR FERAL

It does much harm in destroying sheep. It is famous for its persistent "death-feigning," for an individual has been known to allow part of its skin to be removed, in the belief that it was dead, before betraying its vitality.]

[Ill.u.s.tration: WOODp.e.c.k.e.r, HAMMERING AT A COTTON-REEL, ATTACHED TO A TREE

Notice how the stiff tail-feathers braced against the stem help the bird to cling on with its toes. The original hole, in which this woodp.e.c.k.e.r inserted nuts for the purposes of cracking the sh.e.l.l and extracting the kernel, is seen towards the top of the tree. But the taker of the photograph tied on a hollowed-out cotton-reel as a receptacle for a nut, and it was promptly discovered and used by the bird.]

Experiments in Parental Care

It must be put to the credit of amphibians that they have made many experiments in methods of parental care, as if they were feeling their way to new devices. A common frog lays her clumps of eggs in the cradle of the water, sometimes far over a thousand together; the toad winds two long strings round and between water-weeds; and in both cases that is all. There is no parental care, and the prolific multiplication covers the enormous infantile mortality. This is the sp.a.w.ning solution of the problem of securing the continuance of the race. But there is another solution, that of parental care a.s.sociated with an economical reduction of the number of eggs. Thus the male of the Nurse-Frog (Alytes), not uncommon on the Continent, fixes a string of twenty to fifty eggs to the upper part of his hind-legs, and retires to his hole, only coming out at night to get some food and to keep up the moisture about the eggs. In three weeks, when the tadpoles are ready to come out, he plunges into the pond and is freed from his living burden and his family cares. In the case of the thoroughly aquatic Surinam Toad (Pipa), the male helps to press the eggs, perhaps a hundred in number, on to the back of the female, where each sinks into a pocket of skin with a little lid. By and by fully formed young toads jump out of the pockets.

In the South American tree-frogs called Nototrema there is a pouch on the back of the female in which the eggs develop, and it is interesting to find that in some species what come out are ordinary tadpoles, while in other species the young emerge as miniatures of their parents.

Strangest of all, perhaps, is the case of Darwin's Frog (Rhinoderma of Chili), where the young, about ten to fifteen in number, develop in the male's croaking-sacs, which become in consequence enormously distended.

Eventually the strange spectacle is seen of miniature frogs jumping out of their father's mouth. Needless to say we are not citing these methods of parental care as examples of intelligence; but perhaps they correct the impression of amphibians as a rather humdrum race. Whatever be the mental aspect of the facts, there has certainly been some kind of experimenting, and the increase of parental care, so marked in many amphibians, with a.s.sociated reduction of the number of offspring is a finger-post on the path of progress.

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The Reptilian Mind

We speak of the wisdom of the serpent; but it is not very easy to justify the phrase. Among all the mult.i.tude of reptiles--snakes, lizards, turtles, and crocodiles, a motley crowd--we cannot see much more than occasional traces of intelligence. The inner life remains a tiny rill.

No doubt many reptiles are very effective; but it is an instinctive rather than an intelligent efficiency. The well-known "soft-sh.e.l.l"

tortoise of the United States swims with powerful strokes and runs so quickly that it can hardly be overtaken. It hunts vigorously for crayfish and insect larvae in the rivers. It buries itself in the mud when cold weather comes. It may lie on a floating log ready to slip into the water at a moment's notice; it may bask on a sunny bank or in the warm shallows. Great wariness is shown in choosing times and places for egg-laying. The mother tramps the earth down upon the buried eggs. All is effective. Similar statements might be made in regard to scores of other reptiles; but what we see is almost wholly of the nature of instinctive routine, and we get little glimpse of more than efficiency and endeavour.

In a few cases there is proof of reptiles finding their way back to their homes from a considerable distance, and recognition of persons is indubitable. Gilbert White remarks of his tortoise: "Whenever the good old lady came in sight who had waited on it for more than thirty years, it always hobbled with awkward alacrity towards its benefactress, while to strangers it was altogether inattentive." Of definite learning there are a few records. Thus Professor Yerkes studied a sluggish turtle of retiring disposition, taking advantage of its strong desire to efface itself. On the path of the darkened nest of damp gra.s.s he interposed a simple maze in the form of a part.i.tioned box. After wandering about constantly for thirty-five minutes the turtle found its way through the maze by chance. Two hours afterwards it reached the nest in fifteen minutes; and after another interval of two hours it only required five minutes. After the third trial, the routes became more direct, there was less aimless wandering. The time of the twentieth trial was forty-five seconds; that of the thirtieth, forty seconds. In the thirtieth case, the path followed was quite direct, and so it was on the fiftieth trip, which only required thirty-five seconds. Of course, the whole thing did not amount to very much; but there was a definite learning, _a learning from experience_, which has played an important part in the evolution of animal behaviour.

Comparing reptiles with amphibians, we may recognise an increased masterliness of behaviour and a hint of greater plasticity. The records of observers who have made pets of reptiles suggest that the life of feeling or emotion is growing stronger, and so do stories, if they can be accepted, which suggest the beginning of conjugal affection.

The error must be guarded against of interpreting in terms of intelligence what is merely the outcome of long-continued structure adaptation. When the limbless lizard called the Slow-worm is suddenly seized by the tail, it escapes by surrendering the appendage, which breaks across a preformed weak plane. But this is a reflex action, not a reflective one. It is comparable to our sudden withdrawal of our finger from a very hot cinder. The Egg-eating African snake Dasypeltis gets the egg of a bird into its gullet unbroken, and cuts the sh.e.l.l against downward-projecting sharp points of the vertebrae. None of the precious contents is lost and the broken "empties" are returned. It is admirable, indeed unsurpa.s.sable; but it is not intelligent.

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Mind in Birds

Sight and hearing are highly developed in birds, and the senses, besides pulling the triggers of inborn efficiencies, supply the raw materials for intelligence. There is some truth, though not the whole truth, in the old philosophical dictum, that there is nothing in the intellect which was not previously in the senses. Many people have admired the certainty and alacrity with which gulls pick up a fragment of biscuit from the white wake of a steamer, and the incident is characteristic. In their power of rapidly altering the focus of the eye, birds are unsurpa.s.sed.

To the sense of sight in birds, the sense of hearing comes a good second. A twig breaks under our feet, and out sounds the danger-call of the bird we were trying to watch. Many young birds, like partridges, respond when two or three hours old to the anxious warning note of the parents, and squat motionless on the ground, though other sounds, such as the excited clucking of a foster-mother hen, leave them indifferent.

They do not know what they are doing when they squat; they are obeying the living hand of the past which is within them. Their behaviour is instinctive. But the present point is the discriminating quality of the sense of hearing; and that is corroborated by the singing of birds.

It is emotional art, expressing feelings in the medium of sound. On the part of the females, who are supposed to listen, it betokens a cultivated ear.

[Ill.u.s.tration: THE BEAVER

The beaver will gnaw through trees a foot in diameter; to save itself more trouble than is necessary, it will stop when it has gnawed the trunk till there is only a narrow core left, having the wit to know that the autumn gales will do the rest.]

[Ill.u.s.tration: _Photo: F. R. Hinkins & Son._

THE THRUSH AT ITS ANVIL

The song-thrush takes the snail's sh.e.l.l in its bill, and knocks it against a stone until it breaks, making the palatable flesh available.

Many broken sh.e.l.ls are often found around the anvil.]

As to the other senses, touch is not highly developed except about the bill, where it reaches a climax in birds like the wood-c.o.c.k, which probe for unseen earthworms in the soft soil. Taste seems to be poorly developed, for most birds bolt their food, but there is sometimes an emphatic rejection of unpalatable things, like toads and caterpillars.

Of smell in birds little is known, but it has been proved to be present in certain cases, e.g. in some nocturnal birds of prey. It seems certain that it is by sight, not by smell, that the eagles gather to the carca.s.s; but perhaps there is more smell in birds than they are usually credited with. One would like to experiment with the oil from the preen gland of birds to see whether the scent of this does not help in the recognition of kin by kin at night or amid the darkness of the forest.