Why have certain species ceased to exist? As the individual sickens and dies, so certain species become rare and extinct. Darwin found in Northern Patagonia evidence of the _Equus curvidens_, an extinct species of native American horse. What had caused this species to die out?
Imported horses were introduced at Buenos Ayres in 1537, and so flourished in the wild state that in 1580 they were found as far south as the Strait of Magellan. Darwin was well fitted by the comprehensiveness of his observations to deal with the various factors of extinction and survival. He studied the species in their natural setting, the habitat, and range, and habits, and food of the different varieties. Traveling for three years and a half north and south on the continent of South America, he noticed one species replacing another, perhaps closely allied, species. Of the carrion-feeding hawks the condor has an immense range, but shows a predilection for perpendicular cliffs.
If an animal die on the plain the polyborus has prerogative of feeding first, and is followed by the turkey buzzard and the gallinazo. European horses and cattle running wild in the Falkland Islands are somewhat modified; the horse as a species degenerating, the cattle increasing in size and tending to form varieties of different color. The soil being soft the hoofs of the horse grow long and produce lameness. Again, on the mainland, the niata, a breed of cattle supposed to have originated among the Indians south of the Plata, are, on account of the projection of the lower jaw, unable to browse as effectually as other breeds. This renders them liable to destruction in times of drought. A similar variation in structure had characterized a species of extinct ruminant in India.
How disastrous a great drought might prove to the cattle of the Pampas is shown by the records of 1825 and of 1830. So little rain fell that there was a complete failure of vegetation. The loss of cattle in one province alone was estimated at one million. Of one particular herd of twenty thousand not a single one survived. Darwin had many other instances of nature"s devastations. After the Beagle sailed from the Plata, December 6, 1833, vast numbers of b.u.t.terflies were seen as far as the eye could range in bands of countless myriads. "Before sunset a strong breeze sprung up from the north, and this must have caused tens of thousands of the b.u.t.terflies and other insects to perish." Two or three months before this he had ocular proof of the effect of a hailstorm, which in a very limited area killed twenty deer, fifteen ostriches, numbers of ducks, hawks, and partridges. In the war of extermination that was ever before the great naturalist"s eye in South America, what is it that favors a species" survival or determines its extinction?
Not only is the struggle between the animals and inanimate nature, the plants and inanimate nature, plant and animal, rival animals, and rival plants; it goes on between man and his environment, and, very fiercely, between man and man. Darwin was moved by intense indignation at the slavery on the east coast and the cruel oppression of the laborer on the west coast. He was in close contact with the sanguinary political struggles of South America, and with a war of attempted extermination against the Indian. He refers to the shocking but "unquestionable fact, that [in the latter struggle] all the women who appear above twenty years old are ma.s.sacred in cold blood! When I exclaimed that this appeared rather inhuman, he [the informant] answered, "Why, what can be done? they breed so!""
In all his travels nothing that Darwin beheld made a deeper impression on his sensitive mind than primitive man. "Of individual objects, perhaps nothing is more certain to create astonishment than the first sight in his native haunt of a barbarian--of man in his lowest and most savage state. One"s mind hurries back over past centuries, and then asks, could our progenitors have been men like these?... I do not believe it is possible to describe or paint the difference between savage and civilized man." It was at Tierra del Fuego that he was particularly shocked. He admired the Tahitians; he pitied the natives of Tasmania, corralled like wild animals and forced to migrate; he thought the black aborigines of Australia had been underestimated and remarked with regret that their numbers were decreasing through their a.s.sociation with civilized man, the introduction of spirits, the increased difficulty of procuring food, and contact with European diseases. In this last cause tending to bring about extinction there was a mysterious element. In Chile his scientific ac.u.men had been baffled in the attempt to explain the invasion of the strange and dreadful disease hydrophobia.
In Australia the problem of the transmission to the natives of various diseases, even by Europeans in apparent health, confronted his intelligence. "The varieties of man seem to act on each other in the same way as different specimens of animals--the stronger always extirpating the weaker."
It was at Wollaston Island, near Cape Horn, however, that Darwin saw savage men held in extremity by the hard conditions of life, and at bay.
They had neither food, nor shelter, nor clothing. They stood absolutely naked as the sleet fell on them and melted. At night, "naked and scarcely protected from the wind and rain of this tempestuous climate,"
they slept on the wet ground coiled up like animals. They subsisted on sh.e.l.l fish, putrid whale"s blubber, or a few tasteless berries and fungi. At war, the different tribes are cannibals. Darwin writes, "It is certainly true, that when pressed in winter by hunger, they kill and devour their old women before they kill their dogs." A native boy, when asked by a traveler why they do this, had answered, "Doggies catch otters, old women no." In such hard conditions what are the characteristics that would determine the survival of individual or tribe? One might be tempted to lay almost exclusive emphasis on physical strength, but Darwin was too wise ultimately to answer thus the question that for six or seven years was forming in his accurate and discriminating mind.
On its way west in the Pacific the Beagle spent a month at the Galapagos Archipelago, which lies under the equator five or six hundred miles from the mainland. "Most of the organic productions are aboriginal creations, found nowhere else; there is even a difference between the inhabitants of the different islands; yet all show a marked relationship with those of America." Why should the plants and animals of the islands resemble those of the mainland, or the inhabitants of one island differ from those of a neighboring island? Darwin had always held that species were created immutable, and that it was impossible for one species to give rise to another.
In the Galapagos Archipelago he found only one species of terrestrial mammal, a new species of mouse, and that only on the most easterly island of the group. On the South American continent there were at least forty species of mice, those east of the Andes being distinct from those on the west coast. Of land-birds he obtained twenty-six kinds, twenty-five of which were to be found nowhere else. Among these, a hawk seemed in structure intermediate between the buzzard and polyborus, as though it had been modified and induced to take over the functions of the South American carrion-hawk. There were three species of mocking-thrush, two of them confined to one island each. There were thirteen species of finches, all peculiar to the archipelago. In the different species of geospiza there is a perfect gradation in the size of the beaks, only to be appreciated by seeing the specimens or their ill.u.s.trations.
Few of the birds were of brilliant coloration. The same was true of the plants and insects. Darwin looked in vain for one brilliant flower. This was in marked contrast to the fauna and flora of the South American tropics. The coloration of the species suggested comparison with that of the plants and animals of Patagonia. Amid brilliant tropical plants brilliant plumage may afford means of concealment, as well as being a factor in the securing of mates.
Darwin found the reptiles the most striking feature of the zoology of the islands. They seem to take the place of the herbivorous mammalia.
The huge tortoise (_Testudo nigra_) native in the archipelago is so heavy as to be lifted only by six or eight men. (The young naturalist frequently got on the back of a tortoise, but as it moved forward under his encouragement, he found it very difficult to keep his balance.) Different varieties, if not species, characterize the different islands.
Of the other reptilia should be noted two species of lizard of a genus (_Amblyrhynchus_) confined to the Galapagos Islands. One, aquatic, a yard long, fifteen pounds in weight, with "limbs and strong claws admirably adapted for crawling over the rugged and fissured ma.s.ses of lava," feeds on seaweed. When frightened it instinctively shuns the water, as though it feared especially its aquatic enemies. The terrestrial species is confined to the central part of the group; it is smaller than the aquatic species, and feeds on cactus, leaves of trees, and berries.
Fifteen new species of sea-fish were obtained, distributed in twelve genera. The archipelago, though not rich in insects, afforded several new genera, each island with its distinct kinds. The flora of the Galapagos Islands proved equally distinctive. More than half of the flowering plants are native, and the species of the different islands show wonderful differences. For example, of seventy-one species found on James Island thirty-eight are confined to the archipelago and thirty to this one island.
In October the Beagle sailed west to Tahiti, New Zealand, Australia, Keeling or Cocos Islands, Mauritius, St. Helena, Ascension; arrived at Bahia, Brazil, August 1, 1836; and finally proceeded from Brazil to England. Among his many observations, Darwin noted the peculiar animals of Australia, the kangaroo-rat, and "several of the famous _Ornithorhynchus paradoxus_," or duckbill. On the Keeling or Cocos Islands the chief vegetable production is the cocoanut. Here Darwin observed crabs of monstrous size, with a structure which enabled them to open the cocoanuts. They thus secured their food, and acc.u.mulated "surprising quant.i.ties of the picked fibres of the cocoanut husk, on which they rest as a bed."
In preparing his _Journal_ for publication in the autumn of 1836 the young naturalist saw how many facts pointed to the common descent of species. He thought that by collecting all facts that bore on the variation of plants and animals, wild or domesticated, light might be thrown on the whole subject. "I worked on true Baconian principles, and, without any theory, collected facts on a wholesale scale." He saw that pigeon-fanciers and stock-breeders develop certain types by preserving those variations that have the desired characteristics. This is a process of artificial selection. How is selection made by Nature?
In 1838 he read Malthus" _Essay on the Principle of Population_, which showed how great and rapid, without checks like war and disease, the increase in number of the human race would be. He had seen something in his travels of rivalry for the means of subsistence. He now perceived "that under these circ.u.mstances favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The results of this would be the formation of a new species." As special breeds are developed by artificial selection, so new species evolve by a process of natural selection. Those genera survive which give rise to species adapted to new conditions of existence.
In 1858, before Darwin had published his theory, he received from another great traveler, Alfred Russel Wallace, then at Ternate in the Moluccas, a ma.n.u.script essay, setting forth an almost identical view of the development of new species through the survival of the fittest in the struggle for existence.
REFERENCES
Charles Darwin, _A Naturalist"s Journal_.
Francis Darwin, _The Life and Letters of Charles Darwin_.
W. A. Locy, _Biology and its Makers_ (third revised edition), chap.
XIX.
G. J. Romanes, _Darwin and After Darwin_, vol. I.
A. R. Wallace, _Darwinism_.
See also John W. Judd, _The Coming of Evolution_ (The Cambridge Manuals of Science and Literature).
CHAPTER XVI
SCIENCE AND WAR--PASTEUR, LISTER
In the history of science war is no mere interruption, but a great stimulating influence, promoting directly or indirectly the liberties of the people, calling into play the energy of artisan and manufacturer, and increasing the demand for useful and practical studies. In the activities of naval and military equipment and organization this influence is obvious enough; it is no less real in the reaction from war which impels all to turn with new zest to the arts and industries of peace and to cherish whatever may tend to culture and civil progress.
Not infrequently war gives rise, not only to new educational ideals, but to new inst.i.tutions and to new types of inst.i.tution favorable to the advancement of science. As we have already seen, the Royal Society and Milton"s Academies owed their origin to the Great Rebellion. Similarly the Ecole Polytechnique, mother of many scientific discoveries, rose in answer to the needs of the French Revolution. No less noteworthy was the reconstruction of education under the practical genius of Napoleon I, the division of France into academies, the founding of the lycees, the reestablishment of the great Ecole Normale, and the organization of the Imperial University with new science courses and new provincial Faculties at Rennes, Lille, and elsewhere. With all these different forms in which the influence of war makes itself felt in the progress of science the life and career of Louis Pasteur (1822-1895), the founder of bacteriology, stood intimately a.s.sociated.
He was born at Dole, but the family a few years later settled at Arbois.
For three generations the Pasteurs had been tanners in the Jura, and they naturally adhered to that portion of the population which hailed the Revolution as a deliverance. The great-grandfather was the first freeman of Pasteur"s forbears, having purchased with money his emanc.i.p.ation from serfdom. The father in 1811, at the age of twenty, was one of Napoleon"s conscripts, and in 1814 received from the Emperor, for valor and fidelity, the Cross of the Legion of Honor. The directness and endurance of the influence of this trained veteran on his gifted son a hundred fine incidents attest. In 1848--year of revolt in the monarchies of Europe--the young scientist enrolled himself in the National Guard, and, seeing one day in the Place du Pantheon a structure inscribed with the words _autel de la patrie_, he placed upon it all the humble means--one hundred and fifty francs--then at his disposal.
It was in that same year that Pasteur put on record his discovery of the nature of racemic acid, his first great service to science, from which all his other services were to proceed. As a boy he had attended the _college_ at Arbois where his teacher had inspired him with an ambition to enter the great Ecole Normale. Before reaching that goal he took his bachelor"s degree in science as well as in arts at the Besancon college.
At Paris he came in contact with the leaders of the scientific world--Claude Bernard, Balard, Dumas, Biot.
J. B. Biot had entered the ranks of science by way of the Ecole Polytechnique and the artillery service. In 1819 he had announced that the plane of polarized light--for example, a ray pa.s.sed through Iceland spar--is deflected to right or left by various chemical substances.
Among these is common tartaric acid--the acid of grape-juice, obtained from wine lees. Racemic acid, however, which is identical with tartaric acid in its chemical const.i.tuents, is optically inactive, rotating the plane of polarized light neither to the right nor the left. This substance Pasteur subjected to special investigation. He scrutinized the crystals of sodium ammonium racemate obtained from aqueous solution.
These he observed to be of two kinds differing in form as a right glove from a left, or as an object from its mirror-image. Separating the crystals according to the difference of form, he made a solution from each group. One solution, tested in the polarized-light apparatus, turned the plane to the right; the other solution turned it to the left.
He had made a capital discovery of far-reaching importance, namely, that racemic acid is composite, consisting of dextro-tartaric and laevo-tartaric acids. Biot hesitated to credit a mere tyro with such an achievement. The experiment was repeated in his presence. Convinced by ocular demonstration, he was almost overcome with emotion. "My dear boy," he exclaimed, "I have loved the sciences so much my life through that that makes my heart jump."
Pasteur began his regular professional experience as a teacher of physics in the Dijon lycee, but he was soon transferred to the University of Strasburg (1849). There he married the daughter of the rector of the academie, and three years later became Professor of Chemistry. In 1854 he was appointed Dean of the Faculty of Sciences at Lille, a town then officially described as the richest center of industrial activity in the north of France. In his opening address he showed the value and attractiveness of practical studies. He believed as an educator in the close alliance of laboratory and factory. Application should always be the aim, but resting on the severe and solid basis of scientific principles; for it is theory alone which can bring forth and develop the spirit of invention.
His own study of racemic acid, begun in the laboratories of Paris, and followed up in the factories of Leipzig, Prag, and Vienna, had led to his theory of molecular dissymmetry, the starting point of modern stereo-chemistry. It now gave rise on Pasteur"s part to new studies and to new applications to the industries. He tried an experiment which seems almost whimsical, placing ammonium racemate in the ordinary conditions of fermentation, and observed that only one part--the dextro-rotatory--ferments or putrefies. Why? "Because the ferments of that fermentation feed more easily on the right hand than on the left hand molecules." He succeeded in keeping alive one of the commonest moulds on the surface of ashes and racemic acid, and saw the laevo-tartaric acid appear. It was thus that he pa.s.sed from the study of crystals to the study of ferments.
In the middle of the nineteenth century little was known of the nature of fermentation, though some sought to explain by this ill-understood process the origin of various diseases and of putrefaction. Why does fruit-juice produce alcohol, wine turn to vinegar, milk become sour, and b.u.t.ter rancid? Pasteur"s interest in these problems of fermentation was stimulated by one of the industries of Lille. He was accustomed to visit with his students the factories of that place as well as those of neighboring French and Belgian cities. The father of one of his students was engaged in the manufacture of alcohol from beetroot sugar, and Pasteur came to be consulted when difficulties arose in the manufacturing process. He discovered a relationship between the development of the yeast and the success or failure of the fermentation, the yeast globules as seen under the microscope showing an alteration of form when the fermentation was not proceeding satisfactorily. In 1857 Pasteur on the basis of this study was able to demonstrate that alcoholic fermentation, that is, the conversion of sugar into alcohol, carbonic acid, and other compounds, depends on the action of yeast, the cells of which are widely disseminated in the atmosphere.
In this year of his second great triumph Pasteur was appointed director of science studies in the Ecole Normale, from which he had graduated in 1847. Two years later the loss of his daughter by a communicable disease--typhoid fever--had a great effect on his sensitive and profound mind. Many of his opponents, it is true, found Pasteur implacable in controversy. Undoubtedly he had the courage of his convictions, and his belief that, for the sake of human welfare, right views--_his_ views won by tireless experiment--must prevail, gained him the name of a fighter.
But in all the intimate relations of life his essential tenderness was manifest. Like Darwin he had a horror of inflicting pain, and always insisted, when operations on animals were necessary in the laboratory, on the use of anaesthetics (our command of which had been greatly advanced by Simpson in 1847). Emile Roux said that Pasteur"s agitation at witnessing the slightest exhibition of pain would have been ludicrous if, in so great a man, it had not been touching.
A few months after his daughter"s death Pasteur wrote to one of his friends: "I am pursuing as best I can these studies on fermentation, which are of great interest, connected as they are with the impenetrable mystery of life and death. I am hoping to make a decisive advance very soon, by solving without the least lack of clearness the famous question of spontaneous generation." Two years previously a scientist had claimed that animals and plants could be generated in a medium of artificial air or oxygen, from which all atmospheric air and all germs of organized bodies had been precluded. Pasteur now filtered atmospheric air through a plug of cotton or asbestos (a procedure which had been followed by others in 1854), and proved that in air thus treated no fermentation takes place. Nothing in the atmosphere causes life except the micro-organisms it contains. He even demonstrated that a putrescible fluid like blood will remain unchanged in an open vessel so constructed as to exclude atmospheric dust.
Pasteur"s critics maintained that if putrefaction and fermentation be caused solely by microscopic organisms, then these must be found everywhere and in such quant.i.ties as to enc.u.mber the air. He replied that they were less numerous in some parts of the atmosphere than in others. To prove his contention he set out for Arbois with a large number of gla.s.s bulbs each half filled with a putrescible liquid. The necks of the bulbs had been drawn out and hermetically sealed after the contents had been boiled. In case the necks were broken (to be again sealed immediately), the air would rush in, and (if it held the requisite micro-organisms) furnish the conditions for putrefaction. It was found that in every trial the contents of a certain number of the bulbs always escaped alteration. Twenty were opened in the country near Arbois free from human habitations. Eight out of the twenty showed signs of putrefaction. Twenty were exposed to the air on the heights of the Jura at an alt.i.tude of eight hundred and fifty meters above sea-level; the contents of five of these subsequently putrefied. Twenty others were opened near Mont Blanc at an alt.i.tude of two thousand meters and while a wind was blowing from the Mer de Glace; in this case the contents of only one of the bulbs became putrefied.
While his opponents still professed to believe in the creation of organized beings lacking parents, Pasteur was under the influence of the theory of "the slow and progressive transformation of one species into another," and was becoming aware of phases of the struggle for existence hitherto shrouded in mystery. He wished he said to push these studies far enough to prepare the way for a serious investigation of the origin of disease.
He returned to the study of lactic fermentation, showed that butyric fermentation may be caused by organisms which live in the absence of oxygen, while vinegar is produced from wine through the agency of bacteria freely supplied with the oxygen of the air. Pasteur was seeing ever more clearly the part played by the infinitesimally small in the economy of nature. Without these microscopic beings life would become impossible, because death would be incomplete. On the basis of Pasteur"s study of fermentation, his demonstration that decomposition is owing to living organisms and that minute forms of life spring from parents like themselves, his disciple Joseph Lister began in 1864 to develop antiseptic surgery.
Pasteur"s attention was next directed to the wine industry, which then had an annual value to France of 500,000,000 francs. Might not the acidity, bitterness, defective flavor, which were threatening the foreign sale of French wines, be owing to ferments? He discovered that this was, indeed, the case, and that the diseases of wine could be cured by the simple expedient of heating the liquor for a few moments to a temperature of 50 to 60 C. Tests on a considerable scale were made by order of the naval authorities. The ship Jean Bart before starting on a voyage took on board five hundred liters of wine, half of which had been heated under Pasteur"s directions. At the end of ten months the _pasteurized_ wine was mellow and of good color, while the wine which had not been heated had an astringent, almost bitter, taste. A more extensive test--seven hundred hectoliters, of which six hundred and fifty had been pasteurized--was carried out on the frigate la Sibylle with satisfactory results. Previously wines had been preserved by the addition of alcohol, which made them both dearer and more detrimental to health.
In 1865 Pasteur was called upon to exercise his scientific ac.u.men on behalf of the silk industry. A disease--_pebrine_--had appeared among silkworms in 1845. In 1849 the effect on the French industry was disastrous. In the single _arrondiss.e.m.e.nt_ of Alais an annual income of 120,000,000 francs was lost for the subsequent fifteen years. The mulberry plantations of the Cevennes were abandoned and the whole region was desolate. Pasteur, at the instigation of the Minister of Agriculture, undertook an investigation. After four or five years, in spite of repeated domestic afflictions and the breakdown of his own health, he arrived at a successful conclusion. _Pebrine_, due to "corpuscles" readily detected under the microscope, could be recognized at the moment of the moth"s formation. A second disease, _flacherie_, was due to a micro-organism found in the digestive cavity of the moth.
Measures were taken to select the seed of the healthy moths and to destroy the others. These investigations revealed the infinitesimally small as disorganizers of living tissue, and brought Pasteur nearer his purpose "of arriving," as he had expressed it to Napoleon III in 1863, "at the knowledge of the causes of putrid and contagious diseases."
Returning in July, 1870, from a visit to Liebig at Munich, Pasteur heard at Strasburg of the imminence of war. All his dreams of conquest over disease and death seemed to vanish. He hurried to Paris. His son, eighteen years of age, set out with the army. Every student of the Ecole Normale enlisted. Pasteur"s laboratory was used to house soldiers.
He himself wished to be enrolled in the National Guard, and had to be told that a half-paralyzed man could not render military service. He was obsessed with horror of wanton bloodshed and with indignation at the insolence of armed injustice. Trained to serve his country only in one way he tried, but in vain, to resume his researches. He retired to the old home town of Arbois, and sought to distract his mind from the contemplation of human baseness. Arbois was entered by the enemy in January with the usual atrocities of war. Pasteur accompanied by wife and daughter had gone in search of his son, sick at Pontarlier. The boy was restored to health and returned to his regiment the following month.
During this crisis Pasteur and his friends felt, as many English scientists feel in 1917, in reference to ignorance in high places. "We are paying the penalty," he said, "of fifty years" forgetfulness of science, and of its conditions of development." Again he speaks, as Englishmen to-day very well might, of the neglect, disdain even, of the country for great intellectual men, especially in the realm of exact science. In the same strain his friend Bertin said that after the war everything would have to be rebuilt from the top to the bottom, the top especially. Pasteur recalled the period of 1792 when Lavoisier, Berthollet, Monge, Fourcroy, Guyton de Morveau, Chaptal, Clouet, and other scientists had furnished France with gunpowder, steel, cannon, fortifications, balloons, leather, and other means to repel unjust invasion.