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النشر الإلكتروني

APR23 1927

LIBRARY

THE DARWINIAN THEORY

LECTURE I

HISTORY OF THE THEORY OF EVOLUTION

VERY early in human history the necessity arose for collective names to indicate the various groups and kinds of animals; to distinguish those that were useful for food, clothing, or weapons, &c., from those which were useless or dangerous. An early mode of classification was according to habitat; thus Solomon divided animals into beasts, fowls, creeping things, and fishes. This classification was hardly improved upon till the time of ARISTOTLE, 384322 (?) B.C., a man for whose intellectual power the word stupendous seems barely adequate. Aristotle made many shrewd and acute observations which were not understood at the time, and were rediscovered 2000 years later: he was a man far ahead of his age.

After this follows a great gap in the history. Facts were steadily accumulating, but there was no system or governing principle. Nothing was known of the history of life on earth, and there was indeed Filt

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no idea that there had been such a history. Scattered facts imperfectly ascertained were mixed with much superstition, and associated rather with witchcraft than with science.

LINNÆUS, 1707-1778, was the founder of modern scientific natural history. He was a self-made man, and had a long-continued struggle with poverty during the early part of his career. A botanist from his birth, he was never tired of learning facts about plants. Linnæus was originally intended for the Church, but got on so badly at the schools that in 1727 his father proposed to apprentice him to a shoemaker; however, a friend interested in the young botanist persuaded the father, a poor pastor, to let him learn medicine. With this object in view Linnæus went to Lund, and in 1728 to Upsala. In 1732 he was sent by the Literary and Scientific Society of Upsala to Lapland. In 1735 he went to Holland, and was introduced to Boerhaave, the celebrated physician of Leyden, and by him was introduced to a rich banker, who became his patron and in 1736 sent him to England. He afterwards went to Paris and eventually to Stockholm, where he gained his living by practising as a physician. In 1741 he was appointed Professor of Medicine at Upsala, and at the end of the year exchanged the chair of Medicine for that of Botany and Natural History. His poverty was now over and his fame well established.

Linnæus was a man of extraordinary industry, and sent out his pupils in all directions, thereby collecting information and specimens from every part

of the world, with the minute description, arrangement, and classification of which he charged himself. The first edition of his "Systema Nature" appeared in 1735, and the twelfth edition in 1766. The great merit of Linnæus lay in the fact that he was a man of method, and his strength lay in the orderly arrangement of his knowledge. He introduced a clear, precise, and definite terminology, and that this might be universal he employed Latin, the universal scientific language even at the present day. Still more important than this, he limited and defined the use, not only of words but of names, and established the binomial system. For instance, all roses were called Rosa: the common dog-rose was described as Rosa sylvestris vulgaris, flore odorata incarnato, which means, "The common rose of the woods, with a flesh-coloured sweet-scented flower." This system was sufficient perhaps, but clumsy. As we with our friends find it convenient to use a double name, so with plants and animals Linnæus gave a double name-a generic and a specific, or, as he called it, a "trivial" name. Larger groups of families and orders were defined by a few easily recognised points, such as the number of stamens and pistils in the case of flowers, and the mode of their attachment.

This precise and accurate terminology and orderly arrangement for the first time made it possible to determine the number of different kinds of animals and plants, and to define their characters. This was a service of the utmost importance, and through Linnæus botany first became a science; so also with

zoology, though for a time less perfectly than botany. For the first time it became possible to think or speak of the animal or vegetable kingdom comprehensively, and when a name was used, to know precisely what it signified. This greater exactness at once brought men face to face with the problemWhat is a species? What do we mean by species of animals or plants?

I will illustrate this by examples of what Linnæus meant by species. For instance, the jackdaw, the raven, the rook, and the crow, are all species of the genus Corvus. These birds are clearly more like one another than either of them is like a starling or an eagle; in other words, there is a certain resemblance or affinity between them. Yet, they always differ in certain slight peculiarities of structure, form, and habits; also, they always produce their own kind, and do not interbreed-at any rate, as a rule. The jackdaw (Corvus monedula) is grey at the sides of its neck, and builds its nest in holes or cavities in rocks, churches, chimneys, and uninhabited houses. It feeds chiefly on insects, and is much the smallest of the four birds. The raven (Corvus corax) is the largest of the four, and is black all over. It makes bulky nests on crags or in trees. The rook (Corvus frugilegus) is a trifle smaller than the crow, and lives in noisy flocks. It is black, with a grey forehead and throat. Its nests are found in small trees, often near human habitations. The crow (Corvus corone) is smaller than the raven, and is black, tinged with green on the neck and throat, and purple on the back. So also the lion, tiger, leopard, and domestic cat are all species of one genus, differing in points of structure, size, and habits. Again, the pine, fir, and larch are all species of the genus Pinus.

The idea of a species is therefore one separated by distinctive characters, which are constant and reproduced in the offspring. Jackdaws do not lay eggs from which crows are hatched, nor do cats give birth to lions. Linnæus' idea of species was that they always had been distinct; that at the original stocking of the earth one pair of each kind or species was created, and that the existing species of animals and plants are the direct descendants of these original inhabitants. The initial objection to this view is that, if there were only one pair of each species to start with, they would immediately have eaten one another up, or have themselves died; herbivorous animals devouring plants, and being devoured in their turn by carnivorous animals. Linnæus does not seem to have troubled himself much with the problem, and appears to have adopted the current views of the day without inquiry. The case was, however, different with some of his contemporaries.

BUFFON, 1707-1788, was a contemporary of Linnæus, but a man of very different stamp. He came of a wealthy family, and enjoyed the best education that France could give him. At the age of twenty-one he succeeded to a handsome property, at the very time when Linnæus, with an allowance of £8 a year from his father, was a struggling student at the University of Upsala, putting folded paper into the soles of his

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