Editing Spontaneous generation (section)

=== Aristotle ===
{{further|Aristotle's biology}}

In [[Aristotle's biology|his biological works]], the natural philosopher [[Aristotle]] theorized extensively the reproduction of various animals, whether by [[sexual reproduction|sexual]], [[parthenogenesis|parthenogenetic]], or spontaneous generation. In accordance with his fundamental theory of [[hylomorphism]], which held that every physical entity was a compound of matter and form, Aristotle's basic theory of sexual reproduction contended that the [[semen|male's seed]] imposed form, the set of characteristics passed down to offspring on the "matter" ([[menstrual blood]]) supplied by the female. Thus female matter is the ''[[Four causes#Matter|material cause]]'' of generation—it supplies the matter that will constitute the offspring—while the male semen is the ''[[Four causes#Agent|efficient cause]]'', the factor that instigates and delineates the thing's existence.<ref name=Leroi2014>{{cite book |last=Leroi |first=Armand Marie |author-link=Armand Marie Leroi |title=The Lagoon: How Aristotle Invented Science |title-link=Aristotle's Lagoon |publisher=Bloomsbury |date=2014 |isbn=978-1-4088-3622-4 |pages=215–221}}</ref><ref>{{cite book |editor-last=Brack |editor-first=André |title=The Molecular Origins of Life |year=1998 |publisher=Cambridge University Press |isbn=978-0-521-56475-5 |page=[https://archive.org/details/molecularorigins0000brac/page/1 1] |chapter=Introduction |chapter-url=http://assets.cambridge.org/97805215/64755/excerpt/9780521564755_excerpt.pdf |url=https://archive.org/details/molecularorigins0000brac/page/1 }}</ref> Yet, Aristotle proposed in the ''[[History of Animals]]'', many creatures form not through sexual processes but by spontaneous generation:

{{quote|Now there is one property that animals are found to have in common with plants. For some plants are generated from the seed of plants, whilst other plants are self-generated through the formation of some elemental principle similar to a seed; and of these latter plants some derive their nutriment from the ground, whilst others grow inside other plants ... So with animals, some spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock; and of these instances of spontaneous generation some come from putrefying earth or vegetable matter, as is the case with a number of insects, while others are spontaneously generated in the inside of animals out of the secretions of their several organs.<ref name="HistAnimV">{{cite book |author=Aristotle |author-link=Aristotle |others=translated by D'Arcy Wentworth Thompson |title=History of Animals |url=https://ebooks.adelaide.edu.au/a/aristotle/history/complete.html |orig-year=c. 343 BCE |year=1910 |publisher=Clarendon Press |location=Oxford |chapter=Book V |chapter-url=http://ebooks.adelaide.edu.au/a/aristotle/history/book5.html |isbn=978-90-6186-973-3 |access-date=7 January 2009 |archive-date=8 May 2018 |archive-url=https://web.archive.org/web/20180508025913/https://ebooks.adelaide.edu.au/a/aristotle/history/ |url-status=dead }}</ref>|Aristotle|''[[History of Animals]]'', Book V, Part 1}}

According to this theory, living things may come forth from nonliving things in a manner roughly analogous to the "enformation of the female matter by the agency of the male seed" seen in sexual reproduction.<ref name=Lehoux2017p22>{{cite book |last1=Lehoux |first1=Daryn |title=Creatures Born of Mud and Slime: The Wonder and Complexity of Spontaneous Generation |date=2017 |publisher=Johns Hopkins University Press |location=Baltimore |page=22 |isbn=9781421423814 |url=https://books.google.com/books?id=E749DwAAQBAJ}}</ref> Nonliving materials, like the seminal fluid present in sexual generation, contain ''[[pneuma]]'' (πνεῦμα, "breath"), or "[[vital heat]]". According to Aristotle, ''pneuma'' had more "heat" than regular air did, and this heat endowed the substance with certain vital properties:

{{quote|The power of every soul seems to have shared in a different and more divine body than the so called [four] elements ... For every [animal], what makes the seed generative inheres in the seed and is called its "heat". But this is not fire or some such power, but instead the ''pneuma'' that is enclosed in the seed and in foamy matter, this being analogous to the element of the stars. This is why fire does not generate any animal{{nbsp}}... but the heat of the sun and the heat of animals does, not only the heat that fills the seed, but also any other residue of [the animal's] nature that may exist similarly possesses this vital principle.|Aristotle|''[[Generation of Animals]]'', 736b29ff.<ref>{{cite book |last1=Lehoux |first1=Daryn |title=Creatures Born of Mud and Slime: The Wonder and Complexity of Spontaneous Generation |date=2017 |publisher=Johns Hopkins University Press |location=Baltimore |page=23}}</ref>}}

Aristotle drew an analogy between the "foamy matter" (τὸ ἀφρῶδες, ''to aphrodes'') found in nature and the "seed" of an animal, which he viewed as being a kind of foam itself (composed, as it was, from a mixture of water and ''pneuma''). For Aristotle, the generative materials of male and female animals (semen and menstrual fluid) were essentially refinements, made by male and female bodies according to their respective proportions of heat, of ingested food, which was, in turn, a byproduct of the elements earth and water. Thus any creature, whether generated sexually from parents or spontaneously through the interaction of vital heat and elemental matter, was dependent on the proportions of ''pneuma'' and the various elements which Aristotle believed comprised all things.<ref>{{cite book |last1=Lehoux |first1=Daryn |title=Creatures Born of Mud and Slime |date=2017 |publisher=Johns Hopkins University Press |pages=26–28}}</ref> While Aristotle recognized that many living things emerged from [[Putrefaction|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.<ref>{{cite book |author=Aristotle |author-link=Aristotle |others=translated by Arthur Platt |title=On the Generation of Animals |url=https://ebooks.adelaide.edu.au/a/aristotle/generation/complete.html |access-date=2009-01-09 |orig-year=c. 350 BCE |year=1912 |publisher=Clarendon Press |location=Oxford |chapter=Book III |chapter-url=http://ebooks.adelaide.edu.au/a/aristotle/generation/book3.html |isbn=90-04-09603-5 |archive-date=2015-09-10 |archive-url=https://web.archive.org/web/20150910034528/https://ebooks.adelaide.edu.au/a/aristotle/generation/complete.html |url-status=dead }}</ref>

{{quote|Animals and plants come into being in earth and in liquid because there is water in earth, and air in water, and in all air is vital heat so that in a sense all things are full of soul. Therefore living things form quickly whenever this air and vital heat are enclosed in anything. When they are so enclosed, the corporeal liquids being heated, there arises as it were a frothy bubble.|Aristotle|''[[Generation of Animals]]'', Book III, Part 11}}

With varying degrees of observational confidence, Aristotle theorized the spontaneous generation of a range of creatures from different sorts of inanimate matter. The [[testacea]]ns (a genus which for Aristotle included [[bivalvia|bivalves]] and snails), for instance, were characterized by spontaneous generation from mud, but differed based upon the precise material they grew in—for example, [[clam]]s and [[scallop]]s in sand, [[oyster]]s in slime, and the [[barnacle]] and the [[limpet]] in the hollows of rocks.<ref name=HistAnimV/>