Spontaneous Generation - a look at an old chestnut
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.
Histories of spontaneous generation have made much of a chronological sequence of major figures: F. Redi--> Spallanzani--> Pasteur--> A.I. Oparin--> Stanley Miller & Sidney Fox--> most recently - the astrobiologists. In assigning hero/villain status to their work we may be deceived by concealing how vastly different was the meaning of "experiment" and of "scientific work" in these different times and places. Religions motivations, the views of patrons and audiences, and politics played roles that go far beyond a simple Baconian appeal to the facts. In short, the typical account misses much of the context of an issue which has had so much at stake for Christians.
The first serious attack on the idea of spontaneous generation was made in 1668 by Francesco
Redi, a natural philosopher to the Tuscan court
that had been the patron of Galileo. 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.
Jim Strick comments:
Redis experiments lead off the accounts of both Louis Pasteur and T.H. Huxley, Darwins famous apologist, in their histories of spontaneous generation. Redis experimental approach is touted as pioneering in the development of the method of controlled experimentation. One historian, for instance, claims that "Redi broke with tradition, turned from Aristotle and reliance upon books, and, following an Arab proverb: Experiment augments knowledge, but credulity leads to error, tested the validity of the theory of spontaneous generation by means of simple experiments." This reputation of Redi, and the way in which the simplicity of his experiment lends itself to inclusion in a textbook, have contributed importantly to the writing of the history of spontaneous generation debates as a narrative overwhelmingly dominated by "dueling experiments."
From James Strick, "Darwinism and the Origin of Life: the Role of H. C. Bastian in British Spontaneous Generation Debates, 1868-1873," Journal of the History of Biology 32 (1999): 1-42.
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.
In 1745, John Needham, an English clergyman, proposed what he considered the definitive experiment. Everyone knew that boiling killed microorganisms, so he proposed to test whether or not microorganisms appeared spontaneously after boiling. He boiled chicken broth, put it into a flask, sealed it, and waited - sure enough, microorganisms grew. Needham claimed victory for spontaneous generation.
Critics have portrayed The Comte de Buffon and his collaborator Needham as "armchair philosophers" who cooked up a doctrine of "organic molecules", a vital "plastic force", and "spontaneous generation"; and they had such an inferior microscope that they were able to interpret whatever fuzzy images they saw as supporting the fuzzy ideas they wanted the data to confirm.
An Italian priest, Lazzaro Spallanzani (1770), was not convinced, and he suggested that perhaps the microorganisms 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 vacuum, then boiled the broth. No microorganisms grew. Proponents of spontaneous generation argued that Spallanzani had only proven that spontaneous generation could not occur without air.
Again, I quote Strick
The philosophical background to the Needham/Spallanzani debate has been examined in recent years, highlighting for example that many, such as Bonnet, at that time were deeply committed to ovist preformation (the idea that each egg has contained within it, encased like Russian dolls, all future generations which were to come after). Needham and Buffon, by contrast, argued in favor of epigenesis. One of the main reasons for taking issue with Buffon and Needham was precisely that they claimed that spontaneous generation invalidated the preformation theories so dearly held by many and threatened to thereby undermine the entire Cartesian mechanical Deist worldview. That is to say, their opponents seem to have had at least as much preconceived religious/ philosophical reason for disbelieving in spontaneous generation a priori as Buffon and Needham had for believing in it. Spallanzani eventually came down on the side of preformation and rejected Needhams theory. We would probably admit today that, since his microscope could not have shown him little homunculi inside eggs or sperm cells, Spallanzani, too, must have been willing to go some way in believing in things he could not verify and was thus also operating in an atmosphere of "philosophizing."
At stake also was the fear by many, including Voltaire, that Needhams claims would support atheism and materialism. It was thought by many that this theory implied that life could originate by a chance, random combination of substances. This was so contrary to existing religious beliefs, and to a natural philosophy still very much in the service of demonstrating the existence of a benificent Creator, that it generated heated opposition. As this chance combination of chemicals has become such a crucial element of modern views of the origin of life (such as the work of Stanley Miller), it is interesting that Buffon and Needham are not celebrated as thinkers far ahead of the religious biases of their time. Voltaire seems to have been one of those who most actively spread the opinion that Needham and Buffon were poor scientists, though this was based on seriously misreading Needham.
But these received analyses leave several nagging difficulties when examined closely." Indeed, a close review of the evidence on the actual experiments suggests that this strong case for a predetermination of theory on observation cannot be supported, and that the Buffon experiments can be [viewed as] careful, quality work....Buffon was a critical and self-reflective scientific methodologist whose sophistication in this area has rarely been appreciated. His...methodology involved the dual process of formulation of hypotheses, followed by the testing of these through recurrent observations on concrete phenomena.
Recent study has shown that, Spallanzani, not Buffon and Needham, had the poor microscope and it is not even evident that [objects as small as] bacteria could have been seen with his instrument. The drawings supplied by Spallanzani...strongly suggest that Spallanzanis infusory animalcules are probably protozoans, considerably larger in size than the particles of concern to Buffon and Needham [probably bacteria]...
[However,] the ensuing controversy...reached the level of open acrimony, mutual charges of dishonesty, and claims of observational deception as the century progressed. Needham and Spallanzani, fellow clerics beginning from a point in the 1750s of mutual respect, ended all communication in 1780 in a spirit of distinct bitterness....With others, generally if not exclusively, unable to repeat Buffon and Needhams results, it is little wonder that by the 1780s the weight of scientific opinion had clearly shifted in favor of the critics. The experiments of Needham and Buffon, and the organic molecule theory...became a classic example of a priori science and faulty hypothesis-making. However, the later history of this controversy, as [it emerged in] the debate over Brownian motion, suggests that the Buffon-Needham experiments are to be faulted only by being too advanced for their historical era, raising observational difficulties which others could not, for identifiable technical reasons, resolve. The controversy...presents a classic case in scientific dispute, resembling in at least some respects the famous Pasteur-Pouchet controversy of a century later. There too, through the failure of both parties to discern the importance of the details of the experimental conditions-- the resistance of spores of certain microorganisms to boiling-- the result was an acrimonious debate which was decided in favor of Pasteur well in advance of compelling evidence for his theoretical claims.
James Strick (1999)
Check out the Strick article for the remainder of a retelling of an old story!