CHAPTER XI

THE NATURAL SCIENCES

Manifestations of animal life are everywhere visible. They may be seen on mountain peaks, in desert plains, and by the seashores. Even the bleak arctic ice fields have their faunas. This extraordinary distribution of life has attracted attention since the dawn of history. Primitive man, by his often beautiful cave drawings, indicated that he studied intimately the wild life surrounding him. The basic facts of natural history were studied by the early peoples of the Near East. The Greeks prepared many books on natural history and anticipated modern evolutionary theories. The natural sciences, however, made slow progress until toward the end of the eighteenth century when Linnæus and Buffon began their great works. When the nineteenth century opened, the broader fields of nature were segregated, classified, and described. Linnæus took broad views regarding the principles of classification based upon general structure, and his work was enlarged and improved by Cuvier.

Buffon contributed suggestions regarding the probable mutability of species with respect to changes in environment, and improved on the old Greek evolutionary ideas by formulating a definite theory of the causes of mutability. He was an important agent in promoting the modern theories of evolution in zoölogy and botany, which have done more than anything else to augment our knowledge of terrestrial life.

The numerous scientific exploring expeditions in the eighteenth and nineteenth centuries collected an enormous amount of data regarding animals and animal life. Early in the nineteenth century this data was worked up and classified. It soon became apparent that the range of any given species of animal is strictly limited. A new science, that of the geographical distribution of life, was developed. This has been very fruitful in defining the true home areas of all species of animals, insects, birds, and fish, and locating their principal paths of migration.

The world has been divided into about a dozen terrestrial life regions, subregions and transitional regions. These have been mapped and described. The work of Dr. A. R. Wallace, in 1876, showed the comparative importance and extent of these life zones and their variable richness in zoölogical forms, the relationships of the species in different zones, and their degrees of isolation. The descriptions of these great geographical zones fill many interesting volumes and cover all the important forms of existing life.

The naturalists who studied particular zones, or classes of animals, frequently did extraordinary work. The bird studies in North America, recorded in a series of wonderful paintings by Audubon, and the studies of Fürbringer and other naturalists, are comparable with Wallace's great book on the Geographical Distribution of Animals, published in 1876.

The morphological researches of Parker, Huxley, Quatrefages, Owen, and others revolutionized many of the subdivisions of natural history and led to important discoveries in biology.

The effects of climate upon the development, migration, and decline of species and upon the extension and upbuilding of civilization have been minutely studied. Kropotkin showed that climatic changes in Asia drove the hordes of native tribes into Europe at early periods. They were forced to migrate on account of droughts leading to a food shortage. Many historical events have been shaped by climatic factors. Just as men who inhabit dry districts are usually nomads on account of their need of seeking new food supplies, so animals and insects are forced to migrate for a similar reason. The life changes wrought by disease epidemics under climatic influences have also been studied and have shed much light upon the origin and development of many organs and upon the habits of animals. Some of the chief inferences arising from investigations on the effects of climatic variations on life are that certain types of climate favor the development of certain animal species; certain climates have prevailed in historical times in centers where civilization flourished greatly. Therefore it may be presumed that definite climatic conditions are required for the specific development of each type of species and for each kind of civilization. Just as history shows that one of the many conditions of human progress has changed repeatedly from century to century on account of variations in climatic factors, so these stimuli have, from the earliest times, swayed and modified all classes of organic life. Climate serves to develop, retard, or extinguish animal characteristics, habits, and development. The study of the rôle of climate in modifying living conditions has disclosed data which throws much light on the philosophical problems surrounding organic life, its laws and progress.

The voyage of the _Beagle_ in 1831, for a scientific cruise to South America, with Charles Darwin aboard as naturalist; that of the Ross Antarctic expedition in 1839, with Sir W. J. Hooker as botanist; that of the _Rattlesnake_ for Australia and the South Seas in 1846, with T. H. Huxley as surgeon, resulted in the assembling of scientific data in natural history fields which, when classified and developed, revolutionized the natural sciences.

The work of the _Challenger_, in 1872, and many other memorable British scientific expeditions augmented and confirmed the data collected in the earlier explorations.

Harvey's explanation of the movement of the blood by the pumping pulsations of the heart quickened interest in biology. Mayer and Helmholtz, when chemists, had succeeded in artificially making urea and sugar and investigated living organisms from the viewpoint of mechanisms operated on the principle of the conservation of energy. They traced the manifold functions of the body to chemical and thermal energies developed by the destruction of food.

These valuable discoveries were augmented by Schleiden and Schwann, showing that all organisms are built up of living cells. The offices performed within cells by colloids and solutions, and in the nerves by electric movements, were traced.

Investigations into the most minute forms of animal life also furnished startling results. Schwann found, in 1838, that fermenting yeast consists of living vegetable cells, and that organic putrefaction is caused by the activities of such cells. Louis Pasteur (1822-1895) demonstrated that the presence of bacteria in any animal is always due to the entrance of bacteria and microbes from the outside, or by means favoring the abnormal increase of existing germs. He also showed by experiments that diseases like chicken cholera, phylloxera, or the silkworm disease are caused by particular microbes. These discoveries led to the tracing of many common diseases to their special living germs.

While these impressive additions to scientific knowledge were being made, other naturalists were studying the instinctive emotional and intelligent behavior and psychology of animals, both singly and in herds. Animals and insects were found to display signs of intelligence, sometimes of a high order; to live socially, in many cases; and to play and court with emotional attributes. Throughout the animal kingdom, until man is reached, animals are guided in their activities by self and racial preservation.

Play was found to be a fruitful factor in animal education, even in minute insects. The behavior of any animal does not stand alone, but is related to that of others. Animals which hunt, or are hunted, combatants, rivals, mates, and enemies, react upon one another.

Entomology, the science of insects, has been extensively systematized. Practically every phenomenon relating to the insect metamorphosis has been disclosed. The works of Binet, Lubbock, Fabre, and many others have illuminated the psychology of insect life. The charming writings of J. H. Fabre on the life of a fly, on the mason bees, the hunting wasps, the life of a caterpillar, of a grasshopper, of the sacred beetles and other insects, are as thrilling and instructive as any masterpiece of romantic writing. What could be more interesting than Fabre's account of his observations on the glowworm, when he discovered that its luminescence is due to oxidation by air forces through a special lightning tube, and that it occurs in males as well as females and in the eggs and grubs likewise? He shows that the glowworm's life, from start to finish, is one carnival of light. The females are living lighthouses which brilliantly illumine the wild thyme and other flowering plants they haunt on dark nights, making miniature fairylands in country districts.

Studies in the growth and form of living bodies have opened up many interesting problems in physical biology. The cell and tissue, shell and bone, leaf and flower are various portions of matter, the particles of which are moved, molded, conformed, or shaped in obedience to the laws of physics. Forms like those of the lovely wing scales of butterflies, of lace flies, or the spiral shells of the foraminifera are natural diagrams of the results of physical forces. Biologists not only study the nature of the motions of living organisms as animal kinetics, but also the conformation of the organism itself, whose permanence or equilibrium is explained by the interaction or balance of forces leading to static conditions.

The dynamics of cell formation and cell division and their karyokinetic figure drawings are the result of numerous complex physical force struggles brought about by chemical and physiological reactions. Studies of these have shown that the spermatozoön, nucleus, chromosomes, or the germ plasms, which develop organic life, can never act alone. They must be started by other forces which make them seats of energy.

The experiments of George Rainey on the elementary formation of the skeletons of small animals, of Carpenter upon the formation of shells, and those of Professor Harting on the same subjects, have shown how lime solutions acting in conjunction with gelatinous substances, or membranes, build up the numerous geometric shapes of the frames of so many kinds of primitive organisms, and the scales of fish or the extraordinarily beautiful markings and sculpture of shells.

The application of the Cartesian coordinates to the outline of organisms, skulls, bones, and organs of animals has opened up a new field of mathematics--biological research which has yielded many results confirming theories based on other data and supplying facts of great interest that may at any time result in the establishment of important generalizations.

The fact of beauty in animate nature is so pronounced, and man's contemplative delight in beautiful things is so natural that investigations have been made into the æsthetic emotions of other animals. A vast array of facts has been collected which leaves no doubt of the universal appreciation of beauty. The lovely colors of shells, butterflies and birds, the extraordinary beauty of the designs of the frames of the Foraminifera, radiolarians and sponges, the graceful logarithmic spirals of horns and flower and leaf buds, and the charming flowing lines in the shape of the race horse and gazelle, these elements of organic beauty which emphasize and enhance the forms of animals, all contribute to the general embellishment of nature. The combinations of beauty of form, color, and movements in parrots, humming birds, the fish inhabiting coral reefs, butterflies, and orchids, are always perfect. We likewise find that in all parts of the globe, and in each life zone, organic beauty conforms to that of the landscape and the heavens. The biological significance of this universality of beauty in the organic world will be dealt with in the following chapter.

The fishes of the seas, rivers, streams, and lakes have been studied, classified, and described as completely as the insects of the air, the field, the soil, and those parasitic upon other organisms.

The surveys of the Atlantic have brought to light many types of fish which inhabit only the deepest parts of the ocean. These fish are modified in most extraordinary ways to fit their surroundings. Owing to the darkness of their living zones, they are provided with luminescent appendages which are practically similar to the firefly's and glowworm's electric generators. The lights are formed, as in the insects, by the oxidation of material exuded by the fish.

There are more than 180 families of fishes recorded. Each family contains an average of twenty genera and each genus about five species. The known species of fish are, therefore, between 19,000 and 20,000. The Danish naturalist Hensen found 278,795,000,000 fecundated fish eggs per square mile in the summer waters of the Skagerrack. The waters of the seas from the Arctic to the Antarctic limits are full of fish eggs as well as those of shellfish and sea organisms generally. This shows that organic life is as abundant in the sea as anywhere on land.

Just as temperature and salinity are the chief agents of oceanic circulation and current movements, so they are the leading factors in promoting the organic life of the sea.

The vast heterogeneous mixtures of living creatures, comprising vegetable and animal organisms, larvæ, and eggs of fish and animals, which are swept hither and thither by the sea tides are called plankton. This term means the living dust or emulsion of the sea.

It has been shown that vegetable plankton is composed of bacteria and adult microscopic algæ, largely of the Diatomaceæ, Peridinaceæ, Cyanophyceæ, and other primary groups.

The animal plankton comprises a mass of microscopic creatures belonging to the Protozoa, Radiolaria, and Globeriginæ. There are also immense numbers of tiny, invisible crustaceans like the Copepoda, and eggs and spores of all kinds of fish and algæ. These organisms are so dense in certain sea areas that their particular colorations are reflected in the water. The Red Sea, for example, is colored by a reddish algæ; the Baltic and ocean areas near Greenland are colored green by swarms of algæ, and certain tropical seas are often brilliantly colored in the same manner.

Plankton furnishes fish with nutriment. The study of the movements of plankton, at seasonal intervals, has led to the discovery of the causes, extent, and results of the migration of the principal commercial fishes. These researches are so valuable that most large nations support marine biological stations and ships to regularly make observations. The Norwegian naturalist Särs, Sir John Murray, the Prince of Monaco, and others have furnished accounts of the life histories, feeding grounds, metamorphoses and migrations of many fishes, and have shown how the inhabitants of the plankton masses live upon themselves or produce nitrifying or denitrifying bacteria, chemicals, and mineral substances like lime, phosphates, and horny membranous material.

The development of biology and embryology, and the peculiar habits and color schemes of certain fish, insects, birds, and animals led to inquiries about design in nature, the causes of the development of species, and the instincts and habits of animals. Erasmus, Darwin, Buffon, Cuvier, and others began these studies, but it was Charles Darwin (1809-1882), who by the publication of his "Origin of Species" in 1859, first furnished many of the keys to the riddles of organic life. The next chapter will show what has developed from his labors.