The Evolution Theory, Vol. 1 of 2

by August Weismann

Aristotle was, however, not a systematic zoologist in our sense of the term, as indeed was hardly possible, considering the very small number of animal forms that were known in his time. In our day we have before us descriptions of nearly 300,000 named species wherefrom to construct our classification, while Aristotle knew hardly more than 200. Of the whole world of microscopic animals he could, of course, have no idea, any more than of the remains of prehistoric animals, of which we now know about 40,000 named and adequately described species. One would have thought that it would have occurred to a quick-witted people like the Greeks to pause and ponder when they found mussel-shells and marine snail-shells on the hills far above the sea; but they explained these by the great flood in the time of Deucalion and Pyrrha, and they did not observe that the fossil molluscs were of different species from the similar animals living in the sea in their own day.

Thus there was nothing to suggest to Aristotle and others of his time the idea that a transformation of species had been going on through the ages, and even the centuries after him evoked no such idea, nor did there arise new speculations, after the manner of Empedocles, in regard to the origin of the organic world. On the whole, the knowledge of the living world retrograded rather than advanced until the beginning of the Roman Empire. What Aristotle had known was forgotten, and Pliny's work on animals is a catalogue embellished with numerous fables, arranged according to a purely external principle of division. Pliny divided animals into those belonging to earth, water, and air, which is not very much more scientific than if he had arranged them according to the letters of the alphabet.

During the time of the Roman Empire, as is well known, the knowledge of natural history sank lower and lower; there was no more investigation of nature, and even the physicians lost all scientific basis, and practised only in accordance with their traditional esoteric secrets. As the whole culture of the West gradually disappeared, the knowledge of nature possessed by earlier centuries was also completely lost, and in the first half of the Middle Ages Europeans revealed a depth of ignorance of the natural objects lying about them, which it is difficult for us now to form any conception of.

Christianity was in part responsible for this, because it regarded natural science as a product of heathendom, and therefore felt bound to look coldly on it, if not even to oppose it. Later, however, even the Christian Church felt itself forced to give the people some mental nourishment in the form of natural history, and under its influence, perhaps actually composed by teachers of the Church, there appeared a little book, the so-called Physiologus, which was meant to instruct the people in regard to the animal world. This remarkable work, which has been preserved, must have had a very wide distribution in the earlier Middle Ages, for it was translated into no fewer than twelve languages, Greek, Armenian, Syriac, Arabic, Ethiopic, and so on. The contents are very remarkable, and come from the most diverse sources, that is, from the most different writers of antiquity, from Herodotus, from the Bible, and so forth, but never from original observation. The compilation does not really give descriptions of animals or of their habits, but, of each of the forty-one animals which the Physiologus recognizes, something remarkable is briefly related in true lapidary style, sometimes a mere curiosity without further import, or sometimes a symbolical interpretation. Thus the book says of the panther: 'he is gaily coloured; after satiating himself he sleeps three days, and awakes roaring, giving forth such an agreeable odour that all animals come to him.' Of the pelican the well-known legend is related, that it tears open its own breast to feed its young with its blood, thus standing as a symbol of mother-love. Fabulous creatures, too, appear in these pages. Of the Phœnix, that bird whose plumage glitters with gold and precious stones, which was known even to Herodotus, and which has survived through Eastern fairy-tales on to the time of our own romanticists (Tieck), we read: 'it lives a thousand years, because it has not eaten of the tree of knowledge'; then 'it sets fire to itself and arises anew from its own ashes,' a symbol of nature's infinite power of renewing its youth.

But while among the peoples of Europe all the science of the ancients was lost, except a few barely recognizable fragments, the old lore was preserved, both as regards organic nature and other orders of facts, among the Arabs, through whom so many treasures of antiquity have eventually been handed down to us, coming in the track of the Arabian conquests across North Africa and Spain to the nations of Europe.

It was in this way, too, that the writings of Aristotle again found recognition, after having been translated into Latin at Palermo at the order of that enthusiast for Science and Art, the Hohenstaufen Emperor, Frederick the Second. Our Emperor presented one copy of Aristotle's writings to the University of Bologna, and thus the wisdom of the ancient Greeks again became the common property of European culture. From the thirteenth century to the eighteenth, the study of natural science was limited to repeating and extending the work of Aristotle. Nothing new, depending upon personal observation, was added, and it does not even seem to have occurred to any one to subject the statements of the Stagirite to any test, even when they concerned the most familiar objects. No one noticed the error which ascribed to the fly eight legs instead of six; there was in fact as yet no investigation, and all knowledge of natural history was purely scholastic, and gave absolute credence to the authority of the ancients.

A revulsion, however, occurred in the century of the Reformation, with the breaking down of the blind belief in authority which had till then prevailed in all provinces of human knowledge and thought. After a long and severe struggle, dry scholasticism was finally overcome, and natural science, with the rest, turned from a mere reliance on books to original thinking and personal observation. Thenceforward interpretations of natural processes were sought for no longer in the writings of the ancients, but in Nature herself. Of the magnitude of this emancipation, and of the severity of the struggle against deep-rooted authority, one could form a faint idea from experience even in my own youth. Our young minds were so deeply imbued with the involuntary feeling that the ancients were superior to us moderns in each and every respect, that not only the hardly re-attainable plastic art of the Greeks and the immortal songs of Homer, but all the mental products of antiquity seemed to us models which could never be equalled; the tragedies of Sophocles were for us the greatest tragedies that the world had ever seen, the odes of Horace the most beautiful poems of all time!

In the domain of natural science the new era began with the overthrow of the Ptolemaic cosmogony, which, for more than a thousand years, had served as a basis for astronomy. When the German canon, Nicolas Copernicus (born at Thorn, 1473, died 1543), reversed the old theory, and showed that the sun did not revolve round the earth, but the earth round the sun, the ice was broken and the way paved for further progress. Galilei uttered his famous 'e pur si muove,' Kepler established his three laws of the movements of the planets, and Newton, a century later, interpreted their courses in terms of the law of gravitation.

But we have not here to do with a history of physics or astronomy, and I only wish to recall these well-known facts, in order that we may see how increased knowledge in this domain was always accompanied by advances in that of biology.