Pioneers of Evolution from Thales to Huxley. Edward Clodd

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СКАЧАТЬ and his “betters” clung, as the majority still cling, to the myths of their forefathers. They repaired to the oracles, and watched for the will of the gods in signs and omens.

      In his philosophy Anaxagoras held that there was a portion of everything in everything, and that things are variously mixed in infinite numbers of seeds, each after its kind. From these, through the action of an external cause, called Nous, which also is material, although the “thinnest of all things and the purest,” and “has power over all things,” there arose plants and animals. It is probable, as Professor Burnet remarks, “that Anaxagoras substituted Nous, still conceived as a body, for the Love and Strife of Empedocles simply because he wished to retain the old Ionic doctrine of a substance that ‘knows’ all things, and to identify this with the new theory of a substance that ‘moves’ all things.”

      Thus far speculation has run largely on the origin of life forms, but now we find revival of speculation about the nature of things generally, and the formulation of a theory which links Greek cosmology with early nineteenth-century science with Dalton’s Atomic Theory. Democritus of Abdera, who was born about 460 BC, has the credit of having elaborated an atomic theory, but probably he only further developed what Leucippus had taught before him. Of this last-named philosopher nothing whatever is known; indeed, his existence has been doubted, but it counts for something that Aristotle gives him the credit of the discovery, and that Theophrastus, in the first book of his Opinions, wrote of Leucippus as follows: “He assumed innumerable and ever-moving elements, namely, the atoms. And he made their forms infinite in number, since there was no reason why they should be of one kind rather than another, and because he saw that there was unceasing becoming and change in things. He held, further, that what is is no more real than what is not, and that both are alike causes of the things that come into being; for he laid down that the substance of the atoms was compact and full, and he called them what is, while they moved in the void which he called what is not, but affirmed to be just as real as what is.” Thus did “he answer the question that Thales had been the first to ask.”

      Postponing further reference to this theory until the great name of Lucretius, its Roman exponent, is reached, we find a genuine scientific method making its first start in the person of Aristotle. This remarkable man, the founder of the experimental school, and the Father of Natural History, was born 384 BC at Stagira in Macedonia. In his eighteenth year he left his native place for Athens, where he became a pupil of Plato. Disappointed, as it is thought, at not succeeding his master in the Academy, he removed to Mytilene in the island of Lesbos, where he received an invitation from Philip of Macedon to become tutor to his son, the famous Alexander the Great. When Alexander went on his expedition to Asia, Aristotle returned to Athens, teaching in the “school” which his genius raised to the first rank. There he wrote the greater part of his works, the completion of some of which was stopped by his death at Chalcis in 322. The range of his studies was boundless, but in this brief notice we must limit our survey—and the more so because Aristotle’s speculations outside natural history abound in errors—to his pioneer work in organic evolution. Here, in the one possible method of reaching the truth, theory follows observation. Stagira lay on the Strymonic gulf, and a boyhood spent by the seashore gave Aristotle ample opportunity for noting the variations, and withal gradations, between marine plants and animals, among which last-named it should be noted as proof of his insight that he was keen enough to include sponges. Here was laid the foundation of a classification of life-forms on which all corresponding attempts were based. Then, he saw, as none other before him had seen, and as none after him saw for centuries, the force of heredity, that still unsolved problem of biology. Speaking broadly of his teaching, the details of which would fill pages, its main features are (1) His insistence on observation. In his History of Animals he says “we must not accept a general principle from logic only, but must prove its application to each fact. For it is in facts that we must seek general principles, and these must always accord with facts. Experience furnishes the particular facts from which induction is the pathway to general laws.” (2) His rejection of chance and assertion of law, not, following a common error, of law personified as cause, but as the term by which we express the fact that certain phenomena always occur in a certain order. In his Physics Aristotle says that “Jupiter rains not that corn may be increased, but from necessity. Similarly, if some one’s corn is destroyed by rain, it does not rain for this purpose, but as an accidental circumstance. It does not appear to be from fortune or chance that it frequently rains in winter, but from necessity.” (3) On the question of the origin of life-forms he was nearest of all to its modern solution, setting forth the necessity “that germs should have been first produced, and not immediately animals; and that soft mass which first subsisted was the germ. In plants, also, there is purpose, but it is less distinct; and this shows that plants were produced in the same manner as animals, not by chance, as by the union of olives with grape vines. Similarly, it may be argued, that there should be an accidental generation of the germs of things, but he who asserts this subverts Nature herself, for Nature produces those things which, being continually moved by a certain principle contained in themselves, arrive at a certain end.” In the eagerness of theologians to discover proof of a belief in one God among the old philosophers, the references made by Aristotle to a “perfecting principle,” an “efficient cause,” a “prime mover,” and so forth, have been too readily construed as denoting a monotheistic creed which, reminding us of the “one god” of Xenophanes, is also akin to the Personal God of Christianity. “The Stagirite,” as Mr. Benn remarks (Greek Philosophers, vol. i, p. 312), “agrees with Catholic theism, and he agrees with the First Article of the English Church, though not with the Pentateuch, in saying that God is without parts or passions, but there his agreement ceases. Excluding such a thing as divine interference with all Nature, his theology, of course, excludes the possibility of revelation, inspiration, miracles, and grace.” He is a being who does not interest himself in human affairs.

      But, differ as the commentators may as to Aristotle’s meaning, his assumed place in the orthodox line led, as will be seen hereafter, to the acceptance of his philosophy by Augustine, Bishop of Hippo, in the fourth century, and by other Fathers of the Church, so that the mediæval theories of the Bible, blended with Aristotle, represent the sum of knowledge held as sufficient until the discoveries of Copernicus in the sixteenth century upset the Ptolemaic theory with its fixed earth and system of cycles and epicycles in which the heavenly bodies moved. He thereby upset very much besides. Like Anaximander and others, Aristotle believed in spontaneous generation, although only in the case of certain animals, as of eels from the mud of ponds, and of insects from putrid matter. However, in this, both Augustine and Thomas Aquinas, and many men of science down to the latter part of the seventeenth century, followed him. For example, Van Helmont, an experimental chemist of that period, gave a recipe for making fleas; and another scholar showed himself on a level with the unlettered rustics of to-day, who believe that eels are produced from horse hairs thrown into a pond.

      Of deeper interest, as marking Aristotle’s prevision, is his anticipation of what is known as Epigenesis, or the theory of the development of the germ into the adult form among the higher individuals through the union of the fertilizing powers of the male and female organs. This theory, which was proved by the researches of Harvey, the discoverer of the circulation of the blood, and is accepted by all biologists to-day, was opposed by Malpighi, an Italian physician, born in 1628, the year in which Harvey published his great discovery, and by other prominent men of science down to the last century. Malpighi and his school contended that the perfect animal is already “preformed” in the germ; for example, the hen’s egg, before fecundation, containing an excessively minute, but complete, chick. It therefore followed that in any germ the germs of all subsequent offspring must be contained, and in the application of this “box-within-box” theory its defenders even computed the number of human germs concentrated in the ovary of mother Eve, estimating these at two hundred thousand millions!

      When the “preformation” theory was revived by Bonnet and others in the eighteenth century, Erasmus Darwin, grandfather of Charles Darwin, passed the following shrewd criticism on it: “Many ingenious philosophers have found so great difficulty in conceiving the manner of reproduction in animals that they have supposed all the numerous СКАЧАТЬ