Part 18

Now it is a very interesting fact that the almost certain ancestor of the cultivated wheat is at present living on the arid and rocky slopes of Mount Hermon. It is called _Triticum hermonis_, and it is varying notably to-day, as it did long ago when it gave rise to the emmer, which was cultivated in the Neolithic Age and is the ancestor of all our ordinary wheats. We must think of Neolithic man noticing the big seeds of this Hermon grass, gathering some of the heads, breaking the brittle spikelet-bearing axis in his fingers, knocking off the rough awns or bruising the spikelets in his hand till the glumes or chaff separated off and could be blown away, chewing a mouthful of the seeds--and resolving to sow and sow again.

That was the beginning of a long story, in the course of which man took advantage of the numerous variations that cropped up in this sporting stock and established one successful race after another on his fields. Virgil refers in the "Georgics" to the gathering of the largest and fullest ears of wheat in order to get good seed for another sowing, but it was not till the first quarter of the nineteenth century that the great step was taken, by men like Patrick Sheriff of Haddington, of deliberately selecting individual ears of great excellence and segregating their progeny from mingling with mediocre stock. This is the method which has been followed with remarkable success in modern times.

One of the factors that assisted the Allies in overcoming the food crisis in the darkest period of the war was the virtue of Marquis Wheat, a very prolific, early ripening, hard red spring wheat with excellent milling and baking qualities. It is now the dominant spring wheat in Canada and the United States, and it has enormously increased the real wealth of the world in the last ten years (1921). Now our point is simply that this Marquis Wheat is a fine example of evolution going on. In 1917 upwards of 250,000,000 bushels of this wheat were raised in North America, and in 1918 upwards of 300,000,000 bushels; yet the whole originated from a single grain planted in an experimental plot at Ottawa by Dr. Charles E. Saunders so recently as the spring of 1903.

[Illustration: THE WALKING-FISH OR MUD-SKIPPER (PERIOPHTHALMUS), COMMON AT THE MOUTHS OF RIVERS IN TROPICAL AFRICA, ASIA, AND NORTH-WEST AUSTRALIA

It skips about by means of its strong pectoral fins on the mud-flats; it jumps from stone to stone hunting small shore-animals; it climbs up the roots of the mangrove-trees. The close-set eyes protrude greatly and are very mobile. The tail seems to help in respiration.]

[Illustration: _Photo: "The Times."_

THE AUSTRALIAN MORE-PORK OR PODARGUS

A bird with a frog-like mouth, allied to the British Nightjar. Now in the London Zoological Gardens.

The capacious mouth is well suited for engulfing large insects such as locusts and mantises, which are mostly caught on the trees. During the day the More-pork or Frog-mouth sleeps upright on a branch, and its mottled brown plumage makes it almost invisible.]

[Illustration: PELICAN'S BILL, ADAPTED FOR CATCHING AND STORING FISHES

There is an enormous dilatable sac beneath the lower jaw.]

[Illustration: HORNBILL'S BILL, ADAPTED FOR EXCAVATING A NEST IN A TREE, AND ALSO FOR SEIZING AND BREAKING DIVERSE FORMS OF FOOD, FROM MAMMALS TO TORTOISES, FROM ROOTS TO FRUITS

The use of the helmet or casque is obscure.]

[Illustration: SPOONBILL'S BILL, ADAPTED FOR SIFTING THE MUD AND CATCHING THE SMALL ANIMALS, E.G. FISHES, CRUSTACEANS, INSECT LARVÆ, WHICH LIVE THERE]

[Illustration: FALCON'S BILL, ADAPTED FOR SEIZING, KILLING, AND TEARING SMALL MAMMALS AND BIRDS]

[Illustration: AVOCET'S BILL, ADAPTED FOR A CURIOUS SIDEWAYS SCOOPING IN THE SHORE-POOLS AND CATCHING SMALL ANIMALS]

[Illustration: PUFFIN'S BILL, ADAPTED FOR CATCHING SMALL FISHES NEAR THE SURFACE OF THE SEA, AND FOR HOLDING THEM WHEN CAUGHT AND CARRYING THEM TO THE NEST

The scaly covering is moulted in the autumn.]

We must not dwell too long on this particular instance of evolution, though it has meant much to our race. We wish, however, following Professor Buller's _Essays on Wheat_ (1919), to explain the method by which this good seed was discovered. From one we may learn all. The parent of Marquis Wheat on the male side was the mid-Europe Red Fife--a first-class cereal. The parent on the female side was less promising, a rather nondescript, not pure-bred wheat, called Red Calcutta, which was imported from India into Canada about thirty years ago. The father was part of a cargo that came from the Baltic to Glasgow, and was happily included in a sample sent on to David Fife in Ontario about 1842. From one kernel of this sample David Fife started his stock of Red Fife, which was crossed by Dr. Saunders with Hard Red Calcutta. The result of the cross was a medley of types, nearly a hundred varieties altogether, and it was in scrutinising these that Dr. Saunders hit upon Marquis. He worked steadily through the material, studying head after head of what resulted from sowing, and selecting out those that gave most promise. Each of the heads selected was propagated; most of the results were rejected; the elect were sifted again and yet again, and finally Marquis Wheat emerged, rich in constructive possibilities, probably the most valuable food-plant in the world. It is like a romance to read that "the first crop of the wheat that was destined within a dozen years to overtax the mightiest elevators in the land was stored away in the winter of 1904-5 in a paper packet no larger than an envelope."

Thus from the Wild Wheat of Mount Hermon there evolved one of the most important food-plants of the world. This surely is _Evolution going on_.

§ 2

Changes in the Animal Life of a Country

Nothing gives us a more convincing impression of evolution in being than a succession of pictures of the animal life of a country in different ages. Dr. James Ritchie, a naturalist of distinction, has written a masterly book, _The Influence of Man on Animal Life in Scotland_ (1920), in which we get this succession of pictures. "Within itself," he says, "a fauna is in a constant state of uneasy restlessness, an assemblage of creatures which in its parts ebbs and flows as one local influence or another plays upon it." There are temporary and local changes, endless disturbances and readjustments of the "balance of nature." One year there is a plague of field-voles, perhaps next year "grouse disease" is rife; in one place there is huge increase of starlings, in another place of rabbits; here cockchafers are in the ascendant, and there the moles are spoiling the pasture. "But while the parts fluctuate, the fauna as a whole follows a path of its own. As well as internal tides which swing to and fro about an average level, there is a drift which carries the fauna bodily along an 'irretraceable course.'" This is partly due to considerable changes of climate, for climate calls the tune to which living creatures dance, but it is also due to new departures among the animals themselves. We need not go back to the extinct animals and lost faunas of past ages--for Britain has plenty of relics of these--which "illustrate the reality of the faunal drift," but it may be very useful, in illustration of evolution in being, to notice what has happened in Scotland since the end of the Great Ice Age.

Some nine thousand years ago or more, certain long-headed, square-jawed, short-limbed, but agile hunters and fishermen, whom we call Neolithic Man, established themselves in Scotland. What was the state of the country then?

It was a country of swamps, low forests of birch, alder, and willow, fertile meadows, and snow-capped mountains. Its estuaries penetrated further inland than they now do, and the sea stood at the level of the Fifty-Foot Beach. On its plains and in its forests roamed many creatures which are strange to the fauna of to-day--the Elk and the Reindeer, Wild Cattle, the Wild Boar and perhaps Wild Horses, a fauna of large animals which paid toll to the European Lynx, the Brown Bear and the Wolf. In all likelihood, the marshes resounded to the boom of the Bittern and the plains to the breeding calls of the Crane and the Great Bustard.

Such is Dr. Ritchie's initial picture.

[Illustration: LIFE-HISTORY OF A FROG

1, Before hatching; 2, newly hatched larvæ hanging on to water-weed; 3, with external gills; 4, external gills are covered over and are absorbed; 5, limbless larva about a month old with internal gills; 6, tadpole with hind-legs, about two months old; 7, with the fore-limbs emerging; 8, with all four legs free; 9, a young frog, about three months old, showing the almost complete absorption of the tail and the change of the tadpole mouth into a frog mouth.]

[Illustration: _Photo: J. J. Ward. F.E.S._

HIND-LEG OF WHIRLIGIG BEETLE WHICH HAS BECOME BEAUTIFULLY MODIFIED FOR AQUATIC LOCOMOTION

The flattened tips form an expanding "fan" or paddle, which opens and closes with astonishing rapidity. The closing of the "fan," like the "feathering" of an oar, reduces friction when the leg is being moved forwards for the next stroke.]

[Illustration: THE BIG ROBBER-CRAB (_Birgus Latro_), THAT CLIMBS THE COCO-NUT PALM AND BREAKS OFF THE NUTS

It occurs on islands in the Indian Ocean and Pacific, and is often found far above sea-level. It is able to breathe dry air. One is seen emerging from its burrow, which is often lined with coco-nut fibre. The empty coco-nut shell is sometimes used by the Robber-Crab for the protection of its tail.]

Now what happened in this kingdom of Caledonia which Neolithic Man had found? He began to introduce domesticated animals, and that meant a thinning of the ranks of predacious creatures. "Safety first" was the dangerous motto in obedience to which man exterminated the lynx, the brown bear, and the wolf. Other creatures, such as the great auk, were destroyed for food, and others like the marten for their furs. Small pests were destroyed to protect the beginnings of agriculture; larger animals like the boar were hunted out of existence; others, like the pearl-bearing river-mussels, yielded to subtler demands. No doubt there was protection also--protection for sport, for utility, for æsthetic reasons, and because of humane sentiments; even wholesome superstitions have safeguarded the robin redbreast and the wren. There were introductions too--the rabbit for utility, the pheasant for sport, and the peacock for amenity. And every introduction, every protection, every killing out had its far-reaching influences.

But if we are to picture the evolution going on, we must think also of man's indirect interference with animal life. He destroyed the forests, he cultivated the wild, he made bridges, he allowed aliens, like rats and cockroaches, to get in unawares. Of course, he often did good, as when he drained swamps and got rid of the mosquitoes which once made malaria rife in Scotland.

What has been the net result? Not, as one might think for a moment, a reduction in the _number_ of different kinds of animals. Fourteen or so species of birds and beasts have been banished from Scotland since man interfered, but as far as numbers go they have been more than replaced by deliberate introductions like fallow deer, rabbit, squirrel, and pheasant, and by accidental introductions like rats and cockroaches. But the change is rather in _quality_ than in quantity; the smaller have taken the place of the larger, rather paltry pigmies of noble giants. Thus we get a vivid idea that evolution, especially when man interferes, is not necessarily progressive. That depends on the nature of the sieves with which the living materials are sifted. As Dr. Ritchie well says, the standard of the wild fauna as regards size has fallen and is falling, and it is not in size only that there is loss, there is a deterioration of quality. "For how can the increase of Rabbits and Sparrows and Earthworms and Caterpillars, and the addition of millions of Rats and Cochroaches and Crickets and Bugs, ever take the place of those fine creatures round the memories of which the glamour of Scotland's past still plays--the Reindeer and the Elk, the Wolf, the Brown Bear, the Lynx, and the Beaver, the Bustard, the Crane, the Bumbling Bittern, and many another, lost or disappearing." Thus we see again that evolution is going on.

§ 3

The Adventurers

All through the millions of years during which animals have tenanted the earth and the waters under the earth, there has been a search for new kingdoms to conquer, for new corners in which to make a home. And this still goes on. _It has been and is one of the methods of evolution to fill every niche of opportunity._ There is a spider that lives inside a pitcher-plant, catching some of the inquisitive insects which slip down the treacherous internal surface of the trap. There is another that makes its home in crevices among the rocks on the shore of the Mediterranean, or even in empty tubular shells, keeping the water out, more or less successfully, by spinning threads of silk across the entrance to its retreat. The beautiful brine-shrimp, _Artemia salina_, that used to occur in British salterns has found a home in the dense waters of the Great Salt Lake of Utah. Several kinds of earthworms have been found up trees, and there is a fish, Arges, that climbs on the stones of steep mountain torrents of the Andes. The intrepid explorers of the _Scotia_ voyage found quite a number of Arctic terns spending our winter within the summer of the Antarctic Circle--which means girdling the globe from pole to pole; and every now and then there are incursions of rare birds, like Pallas's Sand-grouse, into Britain, just as if they were prospecting in search of a promised land. Twice or thrice the distinctively North American Killdeer Plover has been found in Britain, having somehow or other got across the Atlantic. We miss part of the meaning of evolution if we do not catch this note of insurgence and adventure, which some animal or other never ceases to sound, though many establish themselves in a security not easily disturbed, and though a small minority give up the struggle against the stream and are content to acquiesce, as parasites or rottenness eaters, in a drifting life of ease.

More important than very peculiar cases is the broad fact that over and over again in different groups of animals there have been attempts to master different kinds of haunts--such as the underground world, the trees, the freshwaters, and the air. There are burrowing amphibians, burrowing reptiles, burrowing birds, and burrowing mammals; there are tree-toads, tree-snakes, tree-lizards, tree-kangaroos, tree-sloths, tree-shrews, tree-mice, tree-porcupines, and so on; enough of a list to show, without mentioning birds, how many different kinds of animals have entered upon an arboreal apprenticeship--an apprenticeship often with far-reaching consequences. What the freeing of the hand from being an organ of terrestrial support has meant in the evolution of monkeys is a question that gives a spur to our imagination.

The Case of the Robber Crab

On some of the coral islands of the Indian and Pacific Oceans there lives a land-crab, Birgus, which has learned to breathe on land. It breathes dry air by means of curious blood-containing tufts in the upper part of its gill-cavity, and it has also rudimentary gills. It is often about a foot long, and it has very heavy great claws, especially on the left-hand side. With this great claw it hammers on the "eye-hole" of a coconut, from which it has torn off the fibrous husk. It hammers until a hole is made by which it can get at the pulp. Part of the shell is sometimes used as a protection for the soft abdomen--for the robber-crab, as it is called, is an offshoot from the hermit-crab stock. Every year this quaint explorer, which may go far up the hills and climb the coco-palms, has to go back to the sea to spawn. The young ones are hatched in the same state as in our common shore-crab. That is to say, they are free-swimming larvæ which pass through an open-water period before they settle down on the shore, and eventually creep up on to dry land. Just as open-water turtles lay their eggs on sandy shores, going back to their old terrestrial haunt, so the robber-crab, which has almost conquered the dry land, has to return to the seashore to breed. There is a peculiar interest in the association of the robber-crab with the coco-palm, for that tree is not a native of these coral islands, but has been introduced, perhaps from Mexico, by the Polynesian mariners before the discovery of America by Columbus. So the learning to deal with coconuts is a recent achievement, and we are face to face with a very good example of evolution going on.

[Illustration: EARLY LIFE-HISTORY OF THE SALMON

1. The fertilised egg, shed in the gravelly bed of the river.

2. The embryo within the egg, just before hatching. The embryo has been constricted off from the yolk-laden portion of the egg.

3. The newly hatched salmon, or alevin, encumbered with its legacy of yolk (Y.S.).

4 and 5. The larval salmon, still being nourished from the yolk-sac (Y.S.), which is diminishing in size as the fish grows larger.

6. The salmon fry about six weeks old, with the yolk fully absorbed, so that the young fish has now to feed for itself. The fry become parr, which go to the sea as smolts, and return as grilse.

In all cases the small figures to the right indicate the natural size.]

[Illustration: THE SALMON LEAPING AT THE FALL IS A MOST FASCINATING SPECTACLE

Again and again we see them jumping out of the seething foam beneath the fall, casting themselves into the curtain of the down-rushing water, only to be carried back by it into the depths whence they have risen. One here and another there makes its effort good, touches the upper lip of the cataract, gives a swift stroke of its tail, and rushes on towards those upper reaches which are the immemorial spawning beds of its race.]

The Story of the Salmon

In late autumn or in winter the salmon spawn in the rivers. The female makes a shallow trough in the gravel by moving her tail from side to side, and therein lays many eggs. The male, who is in attendance, fertilises these with the milt, and then the female covers them deeply with gravel. The process is repeated over and over again for a week or more till all the eggs are shed. For three to four months the eggs develop, and eventually there emerge the larvæ or _alevins_, which lurk among the pebbles. They cannot swim much, for they are encumbered by a big legacy of yolk. In a few weeks, perhaps eight, the protruding bag of yolk has disappeared and the _fry_, about an inch long, begin to move about more actively and to fend for themselves. By the end of the year they have grown to be rather trout-like _parr_, about four inches long. In two years these are double that length. Usually in the second year, but it may be earlier or later, the parr become silvery _smolts_, which go out to sea, usually about the month of May. They feed on young herring and the like and grow large and strong. When they are about three and a half years old they come up the rivers as _grilse_ and may spawn. Or they may pass through the whole grilse stage in the sea and come up the rivers with all the characters of the full-grown fish. In many cases the salmon spawn only once, and some (they are called _kelts_ after spawning) are so much exhausted by starting a new generation that they die or fall a victim to otters and other enemies. In the case of the salmon of the North Pacific (in the genus _Oncorhynchus_, not _Salmo_) all the individuals die after spawning, none being able to return to the sea. It must be remembered that full-grown salmon do not as a rule feed in fresh water, though they may be unable to resist snapping at the angler's strange creations. A very interesting fact is that the salmon keeps as it were a diary of its movements, which vary a good deal in different rivers. This diary is written in the scales, and a careful reading of the concentric lines on the scales shows the age of the fish, and when it went out to sea, and whether it has spawned or not, and more besides.

Interpretation of the Salmon's Story

When an animal frequents two different haunts, in one of which it breeds, it is very often safe to say that the breeding-place represents the original home. The flounder is quite comfortable far up the rivers, but it has to go to the shore-waters to spawn, and there is no doubt that the flounder is a marine fish which has recently learned to colonise the fresh waters. Its relatives, like plaice and sole, are strictly marine. But it is impossible to make a dogma of the rule that the breeding-place corresponds to the original home. Thus some kinds of bass, which belong to the marine family of sea-perches, live in the sea or in estuaries, while two have become permanent residents in fresh water. Or, again, the members of the herring family are very distinctively marine, but the shad, which belong to this family, spawn in rivers and may spend their lives there.

So there are two different ways of interpreting the life-history of the salmon. Some authorities regard the salmon as a marine fish which is establishing itself in fresh water. But others read the story the other way and regard the salmon as a member of a freshwater race, that has taken to the sea for feeding purposes. In regard to trout, we know that the ranks of those in rivers and lakes are continually being reinforced by migrants from the sea, and that some trout go down to the sea while others remain in the freshwater. We know also in regard to a related fish, the char, that while the great majority of kinds are now permanent residents in cold and deep, isolated northern lakes, there are Arctic forms which live in the sea but enter the rivers to spawn. These facts favour the view that the salmon was originally a marine fish. But there are arguments on both sides, and, for our present purpose, the important fact is that the salmon is conquering _two_ haunts. Its evolution is going on.

The Romance of the Eel

Early in summer, at dates varying with the distance of the rivers from the open Atlantic, crowds of young eels or elvers come up-stream. Sometimes the procession or eel-fare includes thousands of individuals, each about the length of our first finger, and as thick as a stout knitting needle. They obey an inborn impulse to swim against the stream, seeking automatically to have both sides of their body equally stimulated by the current. So they go straight ahead. The obligation works only during the day, for when the sun goes down behind the hills the elvers snuggle under stones or beneath the bank and rest till dawn. In the course of time they reach the quiet upper reaches of the river or go up rivulets and drainpipes to the isolated ponds. Their impulse to go on must be very imperious, for they may wriggle up the wet moss by the side of a waterfall or even make a short excursion in a damp meadow.