The origin of life on the earth

chapter 1

CHAPTER 1 THEORIES OF THE SPONTANEOUS GENERATION OF LIFE Ancient and mediaeval beliefs. For many centuries people considered that the Earth was flat and immovable and that the Sun circled round it, rising in the east and hiding itself behind the sea or the mountains in the west. This false belief rested on direct uncritical observation of surrounding natiue. Observations of this kind often suggested that living things, for example insects, worms, and sometimes even fish, birds and mice could not only be born from things like themselves but could also arise fully formed by spontaneous generation, out of mud, dung, earth or other inanimate substances. We may find a belief in the possibility of the spontaneous generation of living things amongst all peoples and at all times; beginning in remote antiquity and finishing in our own days. Even now, in the period of the blossoming of exact science in the culturally advanced nations, it is common for their ordinary inhabitants to be convinced that maggots arise from dung and rotting meat and that various domestic pests arise of their own accord out of rubbish, mud and dirt. These superficial observations miss the fact that dung and filth are to be found in those places where pests lay their eggs from which the new generation of living things develops. Tremendous significance ^vas attached to these everyday, uncritical observations of creation characteristic of ancient peoples, at a time when nature was still not studied in detail, nor submitted to analysis and dissection but was accepted in its entirety as the immediate perception of the intuition. In his book Urzeugung und Lebenskraft, E. O. v. Lippmann^ gives a wide range of material to show how extensively such 1 1 2 THEORIES OF SPONTANEOUS GENERATION beliefs were held. For example, in China in remote times people believed that aphids would grow by spontaneous generation on bamboos if the young shoots were planted out in warm moist weather. In the Indian holy books there are also references to the sudden appearance of various parasites, flies and beetles from sweat and dung. In the cuneiform writings of Babylon one may read that the mud of canals forms Avorms and other animals from its substance.^ In ancient Egypt the view prevailed that the layer of silt left behind after the flooding of the Nile could give rise to living creatures when it was warmed a little by the sun. Frogs, toads, snakes and mice could originate in this way. In this case one might easily convince oneself by direct observation that the front part seemed already finished and alive while the hind part still consisted of undifferentiated damp earth. We also find a repetition of these tales among the ancient Greeks (e.g. Diogenes Apolloniates) and in the writings of the famous Roman sage, Pliny. Such stories were widely current both in the East and the West, in the Middle Ages and far more recently. Shakespeare's audiences were not surprised when Lepidus, in Antony and Cleopatra, asserted that in Egypt crocodiles are produced from the mud of the Nile under the influence of the warm southern sun.^ In general, it appears to be highly characteristic of the history of spontaneous generation that among diverse peoples living at different times and at different cultural stages, w^e almost ahvays find stories of the spontaneous development of organisms of one kind or another. Here maggots arise from dung and rotting meat, here lice form themselves from human sw^eat, here fireflies are born from the sparks of a funeral pyre, and finally, frogs and mice originate from dew and damp earth. Wherever man has met with the un- expected and exuberant appearance of living things he has regarded it as an instance of the spontaneous generation of life. Among the ancient peoples the belief in spontaneous generation did not arise as a consequence of any particular philosophy. For them spontaneous generation was simply an obvious, empirically established fact the theoretical basis of which was of secondary importance. ANCIENT AND MEDIAEVAL BELIEFS $ The ancient teachings of India, Babylon and Egypt bound up the origin of Hfe with various reUgious legends and traditions. From this point of view spontaneous generation was merely a particular manifestation of the creative will of gods or demons. But at the very source of our European culture in ancient Greece, on the replacement of theogony, a mystical interpretation of nature, cosmogony arises as the beginning of scientific investigation. Although all the Greek philosophers from the Miletians to Epicurus and the Stoics acknowledged spontaneous generation as an incontrovertible fact, their philosophical treatment of this fact ^vent far beyond the framework of the previous mystical presentations.^ They contained the beginnings of all the concepts which were developed later in connection with the question of the origin of life. Even the earliest Greek philosopher, Thales, who lived from about 624 to 547 e.g., approached the problem of the essential nature and origin of life from an elementarymaterialist position. Thales and the other philosophers of the Miletian school (Anaximander and Anaximenes) recognised, as a fundamental principle, the objective existence of matter as something which is ahvays living and always changing from the beginning of time. Life is inherent in matter as such. Thus, although the Miletians believed in the spontaneous generation of living things from mud, slime and such materials, they treated this phenomenon as the self- creation of individual organisms, and not as one requiring the intervention of any special mystical force. This point of view was developed later by Empedocles^ (c. 485-425 b.c), who held that plants and animals are formed from substances ^vhich, although not organised, are already living, either by birth fiom things like themselves or from things unlike themselves, i.e., by spontaneous generation. A particularly clear enunciation of the idea of the self-creation of living things is to be found in the works of Democritus^ (460-370 e.g.). In this doctrine ancient Greek materialism reached the height of its development although it had also already acquired a somewhat mechanistic character. According to the view of Democritus matter forms the basis of the universe and consists of a multitude of very small particles (atoms) which 4 THEORIES OF SPONTANEOUS GENERATION are in constant motion and are separated from one another by empty spaces. This mechanical motion of the atoms is inherent in matter, and on it depends the process of organisation of all individual objects. In particular, life appears, not from an act of divine creation, but as the result of the mechanical forces of nature itself. According to Democritus the primary development of living creatures, or their spontaneous development from water and mud, occurs whenminute particles of moist earth come together with atoms of fire in a fortuitous but completely determinate way in the course of their mechanical movement. Another illustrious ancient Greek thinker, Epicurus^ (342-271 B.C.) took up the same philosophical position a hundred years later. We mayfind an exposition of his views in the well-known poem of Lucretius Carus, De rerum natural According to this source, Epicurus taught that, thanks to the moist heat of the sun and the rain, there arise from earth or manure, worms and a multitude of other creatures. But this happens without the participation of any spiritual influence whatever. Spirits, in the form of non-material forces, do not exist, according to Epicurus. The spirit is material and consists of small, very delicate and smooth atoms. The mechanical juxtaposition of atoms in empty space also leads to the formation of multifarious things, in particular, living beings. According to him, the cause of the motion of the atoms resides in matter itself and does not depend on any ' initial impulse ' or other meddling of gods in the affairs of the world. Thus, even hundreds of years before the beginning of our era, the phenomenon of spontaneous generation was explained materialistically by many schools of philosophers as being the self-creation of living things without the participation of any spiritual forces. The matter may be summedup historically by saying that the later development of the idea of spontaneous generation was bound up, not with the materialistic ' line ' of Democritus but with the opposing idealistic ' line ' of Plato. Plato himself (427-347 b.c.) hardly concerned himself directly with the problem of spontaneous generation. In the Phaedohe only touches superficially on the question of the possibility of the formation of living things under the influence of ANCIENT AND MEDIAEVAL BELIEFS

warmth and decay. However, in complete harmony with his general philosophical position, he maintained that life is not inherent in plant and animal matter but this can only be brought to life by the infusion into it of the immortal spirit or Psyched This idea of Plato's played a tremendous part in the later development of the problem in which we are interested. It was reflected to some extent in the teaching of Aristotle which later formed the basis of the mediaeval scientific culture and dominated people's minds for nearly 2000 years. Aristotle (384-322 b.c.) gave to mankind by far the broadest synthesis of the achievements of ancient science, embracing all the factual material ^vhich had been accumulated up till that time. He unfolded his views on the origin of life in a number of biological works concerning the origin of animals: Historia animalium, De partihus animaliiun, and De generatione animalium}'^ According to Aristotle animals are born from others like themselves but equally, they arise and always have arisen by spontaneous generation from nonliving matter. He wrote as follows : Such are the facts, everything comes into being, not only from the mating of animals but from the decay of earth and dung. . . . And among plants the matter proceeds in the same way, some develop from seed, others, as it were, by spontaneous generation by natural forces ; they arise from decaying earth or from certain parts of plants. Ordinary worms, the grubs of bees and wasps and also ticks, greenflies and various other sorts of insects arise, according to Aristotle, from dews in the presence of decaying mud and dimg, from dry trees, hair, sweat and meat. All sorts of intestinal worms are formed from decomposing parts of the body and excreta. Midges, flies, moths, mayflies, dung beetles, cantharides, fleas, bugs and lice (partly as such and partly as grubs) arise from the slime of wells, rivers and seas, from the soil of the fields, from mould and dung, from rot- ting wood and fruit, the dirt of animals, from all sorts of filth, from the sediment of vinegar and also from old wool." Not only insects and worms but other living things can, according to Aristotle, arise by spontaneous generation. Thus 6 THEORIES OF SPONTANEOUS GENERATION