Part 10
_Darwin on Adaptations._—The adaptation of living things to their surroundings has always been a favourite branch of natural history, underrated only by those whose studies are little calculated to inflame the curiosity. Many eminent naturalists have made the interpretation of natural contrivances their chief aim. Darwin equalled the best of his predecessors in accuracy, range, and ingenuity, while he surpassed them all in candour. No one has done so much to vindicate the study of adaptations from all suspicion of triviality, for no one before him had seen so clearly how all new species arise by adaptation of pre-existing ones. It is by adaptation that new forms of life arise; it is inheritance which preserves old ones.
Socrates, Swammerdam, and Paley had drawn from the adaptations of nature proofs of the omnipotence and beneficence of the Creator. Darwin, while admitting that every organism is exquisitely adapted to its own mode of life, believed that the adaptations have been perfected by slow degrees, and that they cannot be proved to have been consciously devised. This interpretation deprives the theologian of valued arguments, but at the same time rids him of difficulties. Even before Darwin's day some few natural theologians had the courage to bring forward instances of the harshness of nature. Kirby and Spence[48] thought that no injustice was done to certain predatory insects by comparing them to devils. Others blessed the mercy of heaven, which, after creating noxious animals, created others to keep them in check. Darwin, when reflecting upon the odious instincts which urge the young cuckoo to eject its foster-brothers, some species of ants to enslave others, and a multitude of ichneumons to lay their eggs in the bodies of live caterpillars, found it a relief to be able to shift the responsibility to an unconscious natural process.[49]
In his autobiography Darwin remarks that he had thought it almost useless to endeavour to prove by indirect evidence that species had been modified until he was able to show how the adaptations could be explained. Some of them alarmed him by their difficulty; to suppose that the eye, with all its inimitable adjustments, had been formed by an unconscious natural process seemed to him absurd until he had traced a good many intermediate steps between the mere colour-spot and the eye of the eagle. He writes to Asa Gray (September 5, 1857) that the facts which had done most to keep him scientifically orthodox were facts of adaptation, the pollen-masses of Asclepias, the mistletoe with its pollen carried by insects and its seeds by birds, the woodpecker exquisitely fitted by feet, tail, beak, and tongue to climb trees and capture insects.
The student of adaptations has no longer a moral thesis to maintain; he tries to understand how a contrivance acts, what advantage it confers upon its possessor, and by what steps it was perfected. The minute variations of species are as capricious as the form of the stones which accumulate at the foot of a precipice; natural selection turns fortuitous variations to account for the advantage of the species as a builder might turn to account the shapes of the stones. Man himself can employ variations for frivolous or even base purposes, as when he produces toy-spaniels or bull-dogs.[50] The adjustments of organic structures often move our wonder by their perfection. One reason why they so far exceed the adjustments made by wind, frost, or moving water is that the process has been so protracted; in a worm or an insect we see the last stage of an adaptation which has been continuously at work for untold geological periods. Another reason is that the thing adapted is alive, sensitive, and capable of responding to the subtlest imaginable influences.
_Darwinism and Non-biological Studies._—The theory of organic evolution has already produced a visible effect upon non-biological studies. Bagehot has applied Darwinian principles to the interpretation of history and politics. Philologists recognise a process very like that of natural selection in the modification of words. The usages of language are inherited from generation to generation; one idiom competes with another, that persisting which best suits the temper or the convenience of the nation. Philology has like zoology its chains of descent, its breeds or dialects, its species or languages, its fossils (dead languages), its dominant and declining forms, its vestiges (such as letters, still retained, though no longer sounded). Psychology is already in part experimental and evolutionary, and seems as if it would attach itself more and more closely to physiology, detaching itself in the same measure from metaphysics. The change may be attributed to two growing convictions: (1) That the experimental method is more trustworthy than the speculative; and (2) that the mind of man is not a thing apart, but an enhanced form of powers manifest in the lower animals. Sociology finds its most practicable and its most urgent sphere of work in the problems of selection and race, which are naturally examined in the light of Darwinian principles. The new study of Comparative Religion aims at the impartial examination of all forms of religious experience, and is evolutionary in proportion as it is scientific. One of its conclusions, by no means universally accepted as yet, is the recognition of conscience as "the organised result of the social experiences of many generations" (Galton). Comparative Religion can already show in outline how by slow degrees magical rites passed into polytheistic worship, how polytheism became simplified and elevated, and how ethical motives at length became influential if not predominant.
Pasteur's Experimental Study of Microbes.
The same difficulty arises with Pasteur as with Darwin; his life-work has already been described often and well. Readers unversed in science have only to turn to the _Vie de Pasteur_, written by his son-in-law, Vallery-Radot, to find a luminous account, giving just so much detail as makes the discoveries intelligible and interesting. If shorter sketches are demanded, they exist. We must therefore above all things be brief, and content ourselves with reminding the reader of facts which, in spite of their recent date, are as well known as anything in the history of science.
Chemists will claim Pasteur as one of their number, and we do not dispute the claim. Trained in experimental methods by the chemical laboratory, he devoted his best powers to the study of living things, and, without ceasing to be a chemist, became one of the greatest of biologists.
Pasteur's chief work was of course the experimental investigation of living particles which float in the air—what we may call _live dust_. Before his day such particles had been seen, named, and classified; some few had been studied in their action and effects. Most of them are plants of low grade, simplified to the last point for the sake of minuteness, on which their ready dispersal depends.
_Yeast._—Van Helmont, early in the seventeenth century, when the microscope had not yet become an instrument of research, attempted to investigate the fermentation of beer, and made acquaintance with the properties of the gas which is evolved, his _gas silvestre_, which was afterwards called fixed air, or carbonic acid. Leeuwenhoek about 1680 examined yeast by his microscopes, and discovered that it is made up of globules which often cohere, and that these globules give off bubbles of gas. Then comes a long interval, during which nothing was done to elucidate the process of fermentation. It was not till 1837 that Caignard-Latour and Schwann, independently of each other, showed that yeast-globules multiply by budding, and are therefore to be set down as living things, probably plants of a simple kind. Twenty years more passed without sensible progress; during this time chemists were striving to prove that the alcohol was produced by contact-action, and that the globules were of no practical importance. By the year 1860 Pasteur was engaged upon the problem. It is well known that he arrived at a firm conviction that living yeast-cells are essential to the production of alcohol. It has since been discovered that the enzyme (unorganised ferment of older writers) secreted by living yeast-cells can change sugar into alcohol after the cells themselves have been destroyed, and that other plants besides yeast-cells secrete the same enzyme when deprived of oxygen.
_Bacteria._—Another and even more important chapter in the history of air-wafted organisms was opened by the indefatigable Leeuwenhoek. In 1683 he wrote a letter to the Royal Society which makes mention for the first time of bacteria, which he found upon his own teeth, and described as minute rods; some of them moved with surprising agility. For nearly two hundred years little more was done. A few bacteria were named and classified, and there the matter rested until Schwann proved experimentally that putrefaction is just as much the work of living microscopic organisms as alcoholic fermentation. In 1857 and the following years Pasteur not only confirmed the work of Schwann, which had been received by the majority of chemists with distrust, but went on to show that the lactic, butyric, and ammoniacal fermentations also depend upon the activity of bacteria. The happy thought struck him that they might be studied alive—a possibility which he soon realised in practice, and upon which the new science of bacteriology largely rests. From about the year 1873 he began to occupy himself seriously with contagion, which he suspected to be connected with specific aerial germs. Davaine and others had years before observed in the blood of sheep and cattle which had died of "charbon" (anthrax) minute "bâtonnets" (bacilli). Pasteur's published results induced Davaine to ask whether his "bâtonnets" might not be the cause of "charbon." Again, it was Pasteur's results which induced Lister to make experiments in the field of antiseptic surgery. Pasteur wasted no time upon the curiosities of bacterial life. His first studies on fermentation suggested that specific diseases may be propagated by microscopic germs, and that such cases of spontaneous generation as had hitherto escaped refutation might be explained by the access of live dust. The identification and biological history of the organisms interested him only as a step towards sure methods of controlling, and, if necessary, destroying, them; of mitigating their virulence by inoculation; of rendering animals immune against them; or of stamping out the disease by isolation. All this is happily too well known for repetition here. The story, with its many dramatic incidents, can be read in the pages of Vallery-Radot.
Hardly less important than the bacteria which destroy life or endanger the products of human industry are the beneficent forms, some of which have in all ages co-operated with man, while others can only be employed by those who possess knowledge and skill. None are so important to our welfare as the bacteria which renew the fertility of the soil. But for the soil-bacteria farm-yard manure would be useless to the crop, for it is they which render it fit for assimilation. Now the bacteria of the soil have their natural enemies, the most mischievous being certain Protozoa, such as Amœba and its kindred. As soon as this fact was grasped, likely remedies were thought of; indeed, one remedy was suggested without any guidance from theory by a vine-grower of Alsace, who treated his soil with carbon disulphide to destroy phylloxera, and found that in so doing he had notably enhanced its fertility. Heating to the temperature of boiling water destroys the soil-protozoa and at the same time the bulk of the soil-bacteria. The bacteria, however, soon multiply more than ever by reason of the absence of their enemies, and a soil cleared of protozoa yields for a few years appreciably richer crops. Of other useful bacteria the briefest notice must suffice. Wine, beer, cheese, and tobacco owe to certain of them distinct flavours, for which the customer is willing to pay high. Leather in certain stages of manufacture, indigo, and woad require the access of other forms. If we also bear in mind the part which yeast plays in the every-day manufacture of bread, wine, and beer, and the part which the vinegar-mould plays in the manufacture of acetic acid, we shall get some notion of the industrial importance of the various micro-organisms. Not a little of the control which we exercise over them we owe directly or indirectly to Pasteur.
The career of Pasteur exhibits a striking unity. His first research, which dealt with a subject so remote from the ordinary studies of the biologist as the crystalline forms of tartrates, made him acquainted with activities, hitherto unsuspected, of minute forms of life. The hope of aiding the industries of Lille, Orleans, and France kept him long engaged upon ferments. If he turned aside to examine the superstition of spontaneous generation, it was to protect his methods from misconstruction. An apparent break in his programme of work was forced upon him by the silkworm pestilence. It proved to be no real break, for pébrine and flacherie were both bacterial diseases. At a comparatively early date (1863) he wrote that his chief ambition was to throw light on the spread of contagious diseases; he could not then foresee that he was destined, not only to elucidate, but in a measure to control them. Around his tomb are inscribed words, each of which commemorates a signal service to his fellow-men: "1848, Molecular dissymetry. 1857, Fermentations. 1862, Spontaneous generation. 1863, Studies of wine. 1865, Silkworm diseases. 1871, Studies on beer. 1877, Contagious diseases of animals. 1880, Vaccination against contagious diseases. 1885, Prevention of hydrophobia." These manifold researches form a continuous chain, each being linked to what precedes and follows. The devotion by which all were inspired, beginning with devotion to science and the fatherland, ended by embracing all mankind.
* * * * *
Biology, which in the sixteenth century sent out only a few feeble shoots, has now become a mighty tree with innumerable fruit-laden branches. The vigour of its latest outgrowths encourages confident hopes of future expansion.
[44] Titius of Wittenberg, who published in 1766 what is commonly called Bode's law of planetary distances, objected to the Linnean system on the ground that it multiplied the principle of division. (_De divisione animalium generali_, 1760.)
[45] _Origin of Species_, chap. xiii.
[46] _Geol. Survey Memoirs_, 1846.
[47] By a curious and no doubt accidental coincidence, Darwin employs the same remarkable metaphor which had occurred to Iordanes in the sixth century A.D. Iordanes calls the north the _officina gentium_.
[48] Introduction to _Entomology_, Introductory Letter.
[49] _Life and Letters_, Vol. I., chap. ii.
[50] Darwin, _Variation of Plants and Animals under Domestication_, Concluding Remarks.
CHRONOLOGICAL TABLE
1200-1850
(The date of a discovery is the date of first publication, where this is known.)
1202. Arabic numeration introduced into Europe by Leonardo of Pisa (Liber Abaci); it spread slowly, and did not become universal till the middle of the seventeenth century.
1214-1294. Roger Bacon.
1265-1321. Dante.
1271-1295. Travels of Marco Polo.
1304~1374. Petrarch.
1324?-1384. Wycliffe.
1340?-1400. Chaucer.
1410. Wood-engraving introduced about this time.
1423. Earliest known block-book.
1450? Mazarin Bible, printed by moveable types.
1453. Taking of Constantinople by the Turks.
1466?-1536. Erasmus.
1471-1528. Albert Durer.
1472-1543. Copernicus.
1475-1564. Michael Angelo.
1477-1576. Titian.
1483-1520. Raphael.
1483-1546. Martin Luther.
1492. First voyage of Columbus.
1497-1498. Voyage of Vasco da Gama to India by the Cape.
1516. More's _Utopia_.
1517. Luther's theses.
1519-1521. Mexico conquered by Cortez.
1519-1522. Circumnavigation of the globe by a ship of Magellan's squadron.
1530-1536. Brunfels' _Herbarum vivæ eicones_. Confession of Augsburg.
1532. Peru conquered by Pizarro.
1534. Society of Jesus founded by Loyola.
1539. Bock's _New Kreutterbuch_ (without figures); 2nd ed. (with figures) 1546.
1542. Fuchs' _Historia Stirpium_.
1543. Copernicus' _De Revolutionibus Orbium Celestium_. Vesalius' _Fabrica Humani Corporis_.
1545. Botanic garden at Padua founded.
1545-1564. Council of Trent.
1547. Botanic garden at Pisa founded.
1551. Belon's _Histoire Naturelle des estranges poissons marins_.
1551-1587. Gesner's _Historia Animalium_.
1553. Belon's _De aquatilibus_, etc., and his _Observations de plusieurs singularitez_, etc. (Travels in the Levant.)
1554. Rondelet's _De piscibus marinis_.
1555. Belon's _Histoire de la nature des Oyseaux_. Rondelet's _Universæ aquatilium Historiæ pars altera_.
1564-1616. Shakespeare.
1564-1642. Galileo.
1566. Revolt of the Netherlands.
1571. Battle of Lepanto (advance of the Turks checked).
1571-1630. Kepler.
1572. Massacre of St. Bartholomew.
1576. L'Obel's _Plantarum seu Stirpium Historia and Adversaria_.
1577-1580. Drake's circumnavigation.
1583. Cesalpini's _De Plantis_.
1588. The Invincible Armada.
1596-1650. Descartes.
1600. Olivier de Serres' _Théâtre d'Agriculture_.
1601. Clusius' _Rariorum plantarum Historia_.
1605. Clusius' _Exoticorum libri decem_.
1610. Galileo'smicroscope invented about this time.
1614. Napier's Logarithms.
1618-1648. Thirty Years' War.
1620. Voyage of _Mayflower_. Bacon's _Novum Organum_.
1621. Aselli re-discovers the lacteals.
1623. C. Bauhin's _Pinax Theatri Botanici_.
1626. Jardin des Plantes founded.
1628. Harvey's _De motu cordis et sanguinis_ published, the lectures had been delivered in 1614.
1635. French Academy founded.
1638. First authenticated cure of fever by chincona bark (in Peru).
1642. New Zealand and Van Dieman's Land discovered by Tasman.
1642-1727. Newton.
1643. Barometer invented by Torricelli.
1650? Air-pump invented by Otto von Guericke. Thoracic duct discovered by Pecquet.
1653. Lymphatic vessels discovered by Rudbeck.
1660. Royal Society founded; incorporated 1662. Boyle's _Spring of Air and its Effects_. Ray's _Catalogus Plantarum circa Cantabrigiam nascentium_.
1661. Boyle's _Sceptical Chemist_. Passage of blood through capillaries observed by Malpighi.
1665. Hooke's _Micrographia_.
1666. Académie des Sciences founded. Composition of white light discovered by Newton.
1668. Redi on the Generation of Insects.
1669. Swammerdam's _Historia Insectorum Generalis_. Malpighi's _De Bombyce_.
1671-1677. Grew's _Anatomy of Plants_; collected in one volume, 1682.
1672-1679. Malpighi's _Anatome Plantarum_; collected in his Opera Omnia, 1686.
1673. Malpighi's _De formatione pulli in ovo_. Leeuwenhoek's first paper published by the Royal Society.
1675. Greenwich Observatory founded. Velocity of light determined by Roemer.
1676. Willughby's _Ornithologia_.
1677. Spermatozoa discovered by Hamm.
1680. Yeast-cells discovered by Leeuwenhoek.
1682. Ray's _Methodus Plantarum_.
1683. Bacteria discovered by Leeuwenhoek.
1687. Newton's _Principia_.
1691-1694. Camerarius on the sexes of flowering plants.
1702. Hydra discovered by Leeuwenhoek.
1711-1776. Hume.
1723-1790. Adam Smith.
1725. Vico's _Scienza Nuova_.
1734-1742. Réaumur's _Histoire des Insectes_.
1736-1810. Watt.
1737. Linnæus's _Systema Naturæ_; last edition by Linnæus, 1766. Linnæus's _Genera Plantarum_.
1737-1738. Swammerdam's _Biblia Naturæ_ published; written long before.
1738. Linnæus's _Classes Plantarum_.
1740-1761. Roesel von Rosenhof's _Insecten-Belustigungen_ begun.
1744. Trembley's _Polype d'eau douce_ (Hydra).
1745. Bonnet's _Traité d'Insectologie_ (aphids, Nais).
1748. Montesquieu's _Esprit des Lois_.
1749-1804. Buffon's _Histoire Naturelle_, the last volumes posthumous.
1752. Identity of lightning and electricity demonstrated by Franklin.
1753. British Museum founded.
1755. Black's experiments on carbonic acid and alkalis.
1759. C. F. Wolff's _Theoria Generationis_.
1760. Lyonet's _Traité Anatomique_, etc. (larva of goat-moth).
1770. New South Wales discovered by Captain Cook.
1775. Priestley's experiments on the restoration by green leaves of air vitiated by combustion or respiration, and on "dephlogisticated air" (oxygen). Adam Smith's _Wealth of Nations_.
1777. Spallanzani's experiments on the spontaneous generation of minute organisms.
1781. Uranus discovered by Herschel. Leroy's _Lettres sur les Animaux_ (first collected edition).
1784. Cavendish's _Experiments on Air_ (composition of water).
1785. Hutton's _Theory of the Earth_.
1787-1789. Lavoisier's _Méthode de nomenclature chimique_ (1787) and _Traité élémentaire de chimie_ (1789).
1789. First French Revolution. A. L. de Jussieu's _Genera Plantarum_. White's _Natural History of Selborne_.
1790. Goethe's _Metamorphosen der Pflanzen_.
1791. Galvani's experiments on animal electricity.
1792. Sprengel's _Entdeckte Geheimniss der Natur_. F. Huber's _Nouvelles Observations sur les Abeilles_.
1796. Cuvier on recent and fossil elephants.
1798. Jenner's _Inquiry_ (vaccination against small-pox). Lithography invented by Senefelder.
1799. William Smith's _Order of the Strata and their Embedded Organic Remains_.
1799-1825. Laplace's _Mécanique Celeste_.
1800. Volta's electric pile.
1807. Dalton's Atomic theory. Davy's decomposition of potash and soda.
1811. Motor and sensory roots of spinal nerves discovered by Bell.
1812. Cuvier's _Ossemens Fossiles_.
1816. Cuvier's _Règne Animal_.
1819. Electro-magnetism discovered by Œrsted. Chamisso's _De Salpa_.
1823-1831. Pollen-tubes traced to the ovule (Amici, Brongniart, Robert Brown).
1827. Discovery of mammalian ovum by Baer.
1828-1837. Baer's _Entwickelungs-geschichte_.
1830-1832. Lyell's _Principles of Geology_.
1835. Cell-division in plants observed by Mohl.
1837. Caignard-Latour's demonstration that alcoholic fermentation is due to living organisms.
1839. Schwann and Schleiden's cell-theory.
1840-1849. Joule's determination of the mechanical equivalent of heat.
1841. Faraday's discovery of electric induction.
1846. Discovery of Neptune by Leverrier and Adams. Agassiz and Buckland's announcement of extensive glaciation in Scotland.
1848. Discovery of the antheridia of ferns by Suminsky.
1849-151. Hofmeister's comparative studies of the higher cryptogams and the flowering plants.
1809-1851. Charles Darwin.
1822-1895. Louis Pasteur.
THE SUB-DIVISIONS OF BIOLOGY
Morphology: Anatomy. Minute Anatomy. Comparative Anatomy.
Embryology.
Physiology (including adaptations to the conditions of life).
Psychology of Animals.
Classification.
Geographical Distribution.
Palæontology.
All these divisions, except Psychology, apply both to plants and animals. Many other modes of division have been proposed.
BIBLIOGRAPHY
[It will be readily understood that the literature of Biology is enormous, as a single fact will show. Half a century ago Dr. Hagen compiled a list of books and papers relating to Entomology alone. Though far from complete, it filled a thousand pages, and if brought down to the present date would probably fill a thousand more. The student who tries to follow in some detail the history of any branch of Biology must read books in half-a-dozen languages, and work continually in large public libraries. We shall attempt no more in this place than to mention a few books which can be procured and read by those whose leisure and knowledge of the subject are limited.]
History of Biology or its Sub-Divisions.
Carus, V. _Geschichte der Zoologie_. 1864 foll.
The French translation by Hagenmuller and Schneider (1880) will be preferred by some.