/home/bea/Documents/CLL/Spontaneous Generation.odt
The slow death of Spontaneous Generation
1668-1859
Russell Levine and Chris Evers
From the time of the ancient Romans, through the Middle Ages, and until the late nineteenth century, it was
generally accepted that some life forms arose spontaneously from non-living matter. Such "spontaneous
generation" appeared to occur primarily in decaying matter. For example, a seventeenth century recipe for the
spontaneous production of mice required placing sweaty underwear and husks of wheat in an open-mouthed
jar, then waiting for about 21 days, during which time it was alleged that the sweat from the underwear would
penetrate the husks of wheat, changing them into mice. Although such a concept may seem laughable today, it
is consistent with the other widely held cultural and religious beliefs of the time.
The first serious attack on the idea of spontaneous
generation was made in 1668 by Francesco Redi, an
Italian physician and poet. At that time, it was widely held
that maggots arose spontaneously in rotting meat. Redi
believed that maggots developed from eggs laid by flies.
To test his hypothesis, he set out meat in a variety of
flasks, some open to the air, some sealed completely, and
others covered with gauze. As he had expected, maggots
appeared only in the open flasks in which the flies could
reach the meat and lay their eggs.
This was one of the first examples of an experiment in
the modern sense, in which controls are used. In spite of
his well-executed experiment, the belief in spontaneous generation remained strong, and even Redi continued
to believe it occurred under some circumstances. The invention of the microscope only served to enhance this
belief. Microscopy revealed a whole new world of organisms that appeared to arise spontaneously. It was
quickly learned that to create "animalcules," as the organisms were called, you needed only to place hay in
water and wait a few days before examining your new creations under the microscope.
The debate over spontaneous generation continued for centuries. In 1745, John Needham, an English
clergyman, proposed what he considered the definitive experiment. Everyone knew that boiling killed
micro-organisms, so he proposed to test whether or not micro-organisms appeared spontaneously after boiling.
He boiled chicken broth, put it into a flask, sealed it, and waited - sure enough, micro-organisms grew.
Needham claimed victory for spontaneous generation.
An Italian priest, Lazzaro Spallanzani, was not convinced, and he suggested that perhaps the micro-organisms
had entered the broth from the air after the broth was boiled, but before it was sealed. To test his theory, he
modified Needham's experiment - he placed the chicken broth in a flask, sealed the flask, drew off the air to
create a partial vacuum, then boiled the broth. No micro-organisms grew. Proponents of spontaneous
generation argued that Spallanzani had only proven that spontaneous generation could not occur without air.
Bea Groves 06/05/2013 Page 1 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
The theory of spontaneous generation was finally laid to rest in 1859 by the young French chemist, Louis
Pasteur. The French Academy of Sciences sponsored a contest for the best experiment either proving or
disproving spontaneous generation. Pasteur's winning experiment was a variation of the methods of Needham
and Spallanzani. He boiled meat broth in a flask, heated the neck of the flask in a flame until it became pliable,
and bent it into the shape of an S. Air could enter the flask, but airborne micro-organisms could not - they
would settle by gravity in the neck. As Pasteur had expected, no micro-organisms grew. When Pasteur tilted the
flask so that the broth reached the lowest point in the neck, where any airborne particles would have settled,
the broth rapidly became cloudy with life. Pasteur had both refuted the theory of spontaneous generation and
convincingly demonstrated that micro-organisms are everywhere - even in the air.
More detail...
Spontaneous generation (also known as 'Aristotelian abiogenesis') is an obsolete body of thought on the ordinary
formation of living organisms without descent from similar organisms. Typically, the idea was that certain forms
such as fleas could arise from inanimate matter such as dust, or that maggots could arise from dead flesh. A
variant idea was that of equivocal generation, in which species such as tapeworms arose from unrelated living
organisms, now understood to be their hosts. Doctrines supporting such processes of generation held that
these processes are commonplace and regular. Such ideas are in contradiction to that of univocal generation:
effectively exclusive reproduction from genetically related parent(s), generally of the same species.
The doctrine of spontaneous generation was coherently 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. Today it is generally accepted to have been decisively dispelled during the 19th
century by the experiments of Louis Pasteur. He expanded upon the investigations of predecessors (such as
Francesco Redi who, in the 17th century, had performed experiments based on the same principles). However,
the experimental difficulties are greater than people might think, and objections from persons holding the
traditional views persisted. Many of these residual objections were routed by the work of John Tyndall,
succeeding the work of Pasteur. Ultimately, the ideas of spontaneous generation were displaced by advances in
germ theory and cell theory.
Disproof of the traditional ideas of spontaneous generation is no longer controversial among professional
biologists. Objections and doubts have been dispelled by studies and documentation of the life cycles of various
life forms. However, the principles of the very different matter of the original abiogenesis on this planet — of
living from non-living material — still are under investigation.
Description
Spontaneous generation refers both to the supposed processes in which different types of life might repeatedly
emerge from specific sources other than seeds, eggs or parents, and also to the theoretical principles which
were presented in support of any such phenomena. Such hypothetical processes sometimes are referred to as
abiogenesis, in which life routinely emerges from non-living matter on a time scale of anything from minutes to
weeks, or perhaps a season or so. An example would be the supposed seasonal generation of mice and other
animals from the mud of the Nile. Such ideas have no operative principles in common with the modern
Bea Groves 06/05/2013 Page 2 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
hypothesis of abiogenesis, in which life emerged in the early ages of the planet, over a time span of at least
millions of years, and subsequently diversified without evidence that there ever has been any subsequent
repetition of the event. Another version of spontaneous generation is variously termed univocal generation,
heterogenesis or xenogenesis, in which one form of life has been supposed to arise from a different form, such
as tapeworms from the bodies of their hosts.
In the decades following the 1859 publication of On the Origin of Species, the term "spontaneous generation"
fell into increasing disfavour. Experimentalists used a variety of terms for the study of the origin of life from
non-living materials. Heterogenesis was applied to once-living materials such as boiled broths, and Henry
Charlton Bastian proposed the term archebiosis for life originating from inorganic materials. The two were
lumped together as "spontaneous generation", but disliking the term as sounding too random, Bastian proposed
biogenesis. In an 1870 address titled, "Spontaneous Generation", Thomas Henry Huxley defined biogenesis as
life originating from other life and coined the negative of the term, abiogenesis, which was the term that
became dominant.
Pre-Aristotelian philosophers
As part of his overall attempt to give natural explanations of things that had previously been ascribed to the
agency of the gods, Anaximander believed that everything arose out of the elemental nature of the universe,
which he called the "apeiron" or "unbounded". According to Hippolytus of Rome 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 speculated that 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 seeds of plants existed in
the air from the beginning, and of animals in the aether.
Bea Groves 06/05/2013 Page 3 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
Aristotle
Aristotle lay the foundations of Western natural philosophy. In his book, The History of Animals, he stated in no
uncertain terms:
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, as is mentioned, by the way, in my treatise on Botany. 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. —Aristotle, History of Animals, Book V, Part 1
According to this theory, living things came forth from non-living things because the non-living 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
by-product of the action of the "sweet" element of water.
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, On the Generation of Animals, Book III, Part 11
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 form 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 benefit from morning light, but not towards the south or the west as those winds generate bookworms.
Aristotle claimed that eels were lacking in sex and lacking milt, spawn and the passages for either. Rather, he
asserted eels emerged from earthworms. Later philosophers dissented. Pliny the Elder did not argue against the
anatomic limits of eels, but stated that eels reproduce by budding, scraping themselves against rocks, liberating
particles that become eels. Athenaeus described eels as entwining and discharging a fluid which would settle on
Bea Groves 06/05/2013 Page 4 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
mud and generate life. On the other hand, Athenaeus also dissented towards spontaneous generation, claiming
that a variety of anchovy did not generate from roe, as Aristotle stated, but rather, from sea foam.
Augustine of Hippo discussed spontaneous generation in The City of God and The Literal Meaning of Genesis,
citing Biblical passages such as "Let the waters bring forth abundantly the moving creature that hath life" (Genesis
1:20) as decrees that would enable ongoing creation.
From the fall of the Roman Empire in 5th century to the East-West Schism in 1054, the influence of Greek
science declined, although spontaneous generation generally went unchallenged. New descriptions were made.
Of the numerous beliefs, some had doctrinal implications outside of the Book of Genesis. For example, the idea
that a variety of bird known as the Barnacle Goose emerged from a crustacean known as the Goose Barnacle,
had implications on the practice of fasting during Lent. In 1188, Gerald of Wales, after having travelled in Ireland,
argued that the "unnatural" generation of barnacle geese was evidence for the Immaculate Conception. Where
the practice of fasting during Lent allowed fish, but prohibited fowl, the idea that the goose was in fact a fish
suggested that its consumption be permitted during Lent. The practice was eventually prohibited by decree of
Pope Innocent III in 1215.
Aristotle, in Arabic translation, was reintroduced to Western Europe. During the 13th century, Aristotle reached
his greatest acceptance. With the availability of Latin translations Saint Albertus Magnus and his student, Saint
Thomas Aquinas, raised Aristotelianism to its greatest prominence. Albert wrote a paraphrase of Aristotle, De
causis et processu universitatis, in which he removed some and incorporated other commentaries by Arabic
scholars. The influential writings of Aquinas, on both the physical and metaphysical, are predominantly
Aristotelian, but show numerous other influences.
Spontaneous generation is discussed as a fact in literature well into the Renaissance. Where, in passing,
Shakespeare discusses snakes and crocodiles forming from the mud of the Nile (Ant 2.7 F1), Izaak Walton again
raises the question of the origin of eels "as rats and mice, and many other living creatures, are bred in Egypt, by
the sun's heat when it shines upon the overflowing of the river...". While the ancient question of the origin of eels
remained unanswered and the additional idea that eels reproduced from corruption of age was mentioned, the
spontaneous generation of rats and mice engendered no debate.
The Dutch biologist and microscopist Jan Swammerdam (1637 - 1680) rejected the concept that one animal
could arise from another or from putrification by chance because it was impious and like others found the
concept of spontaneous generation irreligious, and he associated it with atheism and Godless opinion.
Modern origins of life research
Oparin's book The Origin of Life in 1924, in which he proposed a chemical theory of the origin of life, was not
published in English until 1936. Prior to that, it had been relatively uninfluential except in his native Soviet Union.
Oparin (1894-1980) was personally well regarded in the Soviet Union, and was elected early to the Academy of
Sciences. He was also unfortunately involved in the Lysenkoist débâcle in Soviet genetics, and declared overtly
that his views were compatible with the "dialectical materialism" of Soviet Leninism. However, despite this, it
appears that the more important influence was the impact of colloid chemistry, then making great strides.
Bea Groves 06/05/2013 Page 5 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
Oparin's hypothesis was this: gels arose out of colloidal solutions which reacted in a way to cause more gels to
be formed of the same chemical constitution. As the material in the surrounding watery medium
diminished,"the more strongly and bitterly the struggle for existence was waged", so that gels either became
"cannabilistic" or evolved to become autotrophs (organisms that metabolise non-living material, such as algae).
He reasoned that if the early atmosphere lacked free oxygen, which is a product of plant respiration, simple
organic compounds formed by vulcanism or lightning, containing the chemical elements that make up life Carbon, Hydrogen, Oxygen, and Nitrogen - would not be destroyed, but would accumulate, forming a broth of
organic molecules.
Before Oparin's work became known, the English biochemist J. B. S. Haldane, who had since 1923 been working
on enzymes, wrote his paper in 1929, published in The Rationalist Annual, on the origin of life, in which he
stated that, as a result of biochemistry, "since his [Pasteur's] death the gap between life and matter has been
greatly narrowed", and, influenced by d'Hérelle, thought that the bacteriophage was a "step beyond the enzyme
on the road to life, but it is perhaps an exaggeration to call it fully alive". The precursors of life were like viruses,
due to anaerobic fermentation for millions of years.
Despite many arguments, largely theoretical but with some experimental work, spontaneous generation
remained a viable option for the origins of life - for abiogenesis - but it was a very confused field. What caused
it to change and become focused was the publication on 23 April 1953 of Crick and Watson's Nature paper on
the structure of DNA. Three weeks later, a graduate student at the University of Chicago named Stanley Miller
published a paper in Science, on 15 May, entitled "A production of amino acids under possible primitive earth
conditions".
Miller was a doctoral student of Nobel laureate Harold C. Urey (a chemist who discovered deuterium), after he
heard a lecture by Urey in which he noted in passing that earth's primordial hydrogen-rich (reducing)
atmosphere would have been favourable for the formation of simple organic molecules. He decided, with Urey's
permission, to test this, assuming an atmosphere of molecular hydrogen (H2), methane (CH4), ammonia (NH3)
and water vapour (H2O). Neither Urey nor Miller knew at this point that this was in line with Oparin's
hypothesis, but as he prepared for the experiments, Miller read Oparin and mulled it over, along with Urey's
hypotheses on the formation of the solar system.
He passed the atmosphere through a glass retort, continuously cycling it for several days, while exposing it to
heat, electrical arcing, and cooling. After two days, the "ocean" (a flask of water through which the gases were
passed) became pale yellow, and on analysis this turned out to be glycine, the simplest amino acid. They
repeated the experiment for a week, and in the final yellow-brown solution, Miller detected seven amino acids,
including three (glycine, anine and aspartic acid) found in modern living systems. In a period of three and a half
months, Miller had confirmed Urey's and Oparin's hypotheses on the formation of the precursor molecules of
life. The claim was never that life had been made, but only that the necessary molecules for life could form
spontaneously. Since Wöhler synthesised urea in 1828, this was becoming an inevitable conclusion - the
molecular nature of life was more and more widely accepted and applied. Now there was no need to think that
organic molecules had to come from organic systems. Later experiments use a more realistic atmosphere,
replacing methane with carbon monoxide or dioxide (CO or CO2), or ammonia with molecular nitrogen (N2), with
similar results.
Bea Groves 06/05/2013 Page 6 of 7
/home/bea/Documents/CLL/Spontaneous Generation.odt
An alternative to the Oparin-Miller model was proposed by Günter Wächtershäuser, who suggested that carbon
oxides released from deep sea vents could stabilise on iron-sulphates, reacting with molecular hydrogen to form
organic monomers (simple molecular units) from which life could form. Others have included the roles of clay
substrates as catalytic templates for molecules to form on before there were genes, the formation of organic
molecules in space (now well-established) seeding the early earth, and a formal model by Manfred von Eigen of
how chemical reactions might generate copies of themselves - the hypercycle.
Sidney Fox successfully synthesised coascervate "cells" (a coascervate is a mixture of colloids that can, like
lipids in modern cells, form a layer that will enclose molecules, but which can allow monomers to pass across
it). These will, under some conditions, divide as they "grow" to form new cells.
Conclusions
1.
In the initial period of biology it was assumed that life was a special substance, and that it could
generate living beings directly. As research into the life-cycles of animals, plants and diseases
progressed, it became obvious that modern living forms were always observed to form from existing
living forms, and that cells always came from existing cells.
2. At the same time, it became increasingly obvious that the gap between living things at the chemical
level and non-living molecules was decreasing, until it became clear in the mid-20th century that all
processes of living things were chemical, and there was no "vital principle" needed for life.
3. Opposition to abiogenesis has sometimes been due to philosophical or religious principles, but also the
state of scientific knowledge at the time. However, it is not feasible now, with our increasing knowledge
of the chemistry of life and of prebiotic earth.
4. None of the people who did crucial experiments on spontaneous generation disproved abiogenesis. At
best, they strongly confirmed the hypothesis that modern organisms (mice, maggots, or germs) did not
arise in ordinary cases out of non-living material. Most of the experiments against spontaneous
generation were posed against heterogenesis, the doctrine that life could form from the decayed
products of living organisms.
5. Pasteur did not disprove the origin of life by natural means, and the saying "all cells from cells" was not
intended to cover the initial period of life on earth. Darwin did not propose a theory of the origin of life
in the beginning.
6. Evolutionary theory was not proposed to account for the origins of living beings, only the process of
change once life exists. However, many have thought that the theory of evolution logically requires a
beginning of life, which is true. Of those, many have thought that a natural account of the origin of life
is necessary, and some have proposed models which have borne up or not as research proceeds.
Bea Groves 06/05/2013 Page 7 of 7