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Spontaneous generation
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Spontaneous generation or Equivocal generation is an obsolete theory regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from Univocal generation, or reproduction from parent(s). The theory was synthesized by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia.
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Encyclopedia
Spontaneous generation or Equivocal generation is an obsolete theory regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from Univocal generation, or reproduction from parent(s). The theory was synthesized by Aristotle, who compiled and expanded the work of prior natural philosophers and the various ancient explanations of the appearance of organisms; it held sway for two millennia. It is generally accepted to have been ultimately disproven in the 19th Century by the experiments of Louis Pasteur, expanding upon the experiments of other scientists before him. Ultimately, it was succeeded by germ theory and cell theory.
The disproof of ongoing spontaneous generation is no longer controversial, now that the life cycles of maggots and other pests have been well documented. However, the question of abiogenesis, how living things originally arose from non-living material, remains relevant today.
Description
Spontaneous generation refers to both the supposed process by which life would systematically emerge from sources other than seeds, eggs or parents and to the theories which explained the apparent phenomenon. The first form is abiogenesis, in which life emerges from non-living matter. This should not be confused for the modern hypothesis of abiogenesis, in which life emerged once and diversified. The second version is heterogenesis (sometimes called xenogenesis), in which one form of life emerges from a different form.
Pre-Aristotelian Philosophers
Anaximander believed that everything arose out of the elemental nature of the universe, which he called the "apeiron" or "unbounded". As part of his overall attempt to give natural explanations of things that had previously been ascribed to the agency of the gods. According to Hippolytus in the third century CE, Anaximander claimed that living creatures were first formed in the "wet" when acted on by the Sun, and that they were different then than they are now. For example, he claimed humans, in a different form, must have earlier been born mature like other animals, or they would not have survived. Anaximander also claimed that spontaneous generation continued to this day, with aquatic forms being produced directly from lifeless matter.
Anaximenes, a pupil of Anaximander, thought that air was the element that imparted life, motion and thought, and supposed there was a primordial terrestrial slime, a mixture of earth and water, which when combined with the sun's heat, formed plants, animals and human beings directly.
Xenophanes, traced the origin of man back to the transitional period between the fluid stage of the earth and the formation of land. He too held to a spontaneous generation of fully formed plants and animals under the influence of the sun.
Empedocles accepted the spontaneous generation of life, but held that there had to be trials of combinations of parts of animals that spontaneously arose. Successful combinations formed the species we now see, unsuccessful forms failed to reproduce.
Anaxagoras also adopted a terrestrial slime account, although he thought that the germs (seeds) of plants existed in the air from the beginning, and of animals in the ether.
Aristotle
Aristotle lay the foundations of Western natural philosophy. In his book, The History of Animals, he stated in no uncertain terms:
According to this theory, living things came forth from nonliving things because the nonliving material contained pneuma, or "vital heat". The creature generated was dependent on the proportions of this pneuma and the five elements he believed comprised all matter. While Aristotle recognized that many living things emerged from putrefying matter, he pointed out that the putrefaction was not the source of life, but the byproduct of the action of the "sweet" element of water.
Numerous forms were attributed to various sources. The testaceans (shelled molluscs) are characterized by forming by spontaneous generation in mud, but differ based upon the material they grow in — for example, clams and scallops in sand, oysters in slime, and the barnacle and the limpet in the hollows of rocks. Some reddish worms forms from long-standing snow which has turned reddish. Another grub was said to grow out of fire.
Concerning sexual reproduction, Aristotle argued that the male parent provided the "form," or soul, that guided development through semen, and the female parent contributed unorganized matter, allowing the embryo to grow.
Classical writers after Aristotle
Vitruvius, a Roman architect and writer of the 1st century BCE, advised that libraries be placed facing eastwards to benefits from morning light, but not towards the south or the west as those winds generate bookworms.
Aristotle claimed that eels were lacking in gender and lacking milt, spawn and the passages for either.
Adoption in Christianity
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