Tag Archives: Spontaneous Generation

April 7, 1864 (a Thursday)

On this date, Louis Pasteur uttered his famous statement, “The doctrine of spontaneous generation will never recover from the mortal blow inflicted by this experiment,” during an address he delivered at the Sorbonne in Paris, France. The experiment he was referring to involved swan-necked flasks.

Pasteur filled a flask with medium, heated it to kill all life, and then drew out the neck of the flask into a long S. This prevented microorganisms in the air from entering the flask, yet allowed air to flow freely. If the swan neck was broken, microbes could enter the flask and grow.

Pasteur had placed beef broth in flasks that had open-ended, long necks. After bending the necks of the flasks into S-shaped curves that dipped downward, then swept sharply upward, he boiled the contents. The contents of these uncapped flasks remained uncontaminated even months later.

Pasteur explained that the S-shaped curve allowed air to pass into the flask; however, the curved neck trapped airborne microorganisms at the bottom of the curve, preventing them from traveling into the broth.  If the swan neck was broken, microbes readily entered the flask and grew. Thus, Pasteur demonstrated that (1) microorganisms are present in the air and can contaminate solutions; and (2) the air itself does not create microbes.

Interestingly, despite Pasteur’s successful demonstrations against spontaneous generation, attempts to repeat his experiments occasionally failed because, after some time, microbial growth occurred in some broths of swan-necked flasks. This created doubt in the minds of many. But, this problem was solved by John Tyndall, an English physicist, in the year 1877. He explained that bacteria exist in two forms: Heat-labile forms which could be killed by exposure to high temperatures, and heat-resistant forms (known as spores) which could not be killed by continuous boiling of the broth.  After the broth has cooled, the latter resulted in microbial growth in such broths.

Tyndall further stated that if such broths are subjected to intermittent boiling (that is, discontinuous boiling) on successive occasions, a process now popular as tyndallization, the heat-resistant forms of bacteria will be killed and the broths become completely free of them, and do not show any microbial growth. It so happens because the first boiling kills vegetative cells of bacteria but spores remain as such. The spores now germinate in cooled broth and produce new bacteria cells which are killed during further boiling and so on. In this way, Tyndall validated Pasteur’s results and helped end the debate on spontaneous generation.

Many creationists maintain that, as a result of the above experiment, “Louis Pasteur disproved Darwin’s theory.” In fact, Pasteur did no such thing. What he and the others who denied spontaneous generation demonstrated is that life does not currently spontaneously arise in complex form from non-life in nature; he did not demonstrate the impossibility of life arising in simple form from non-life by way of a long and propitious series of chemical steps/selections. Pasteur’s experiments were limited to a smaller system, and for a shorter time, than the open surface of the planet over millions or billions of years. In particular, they did not show that life cannot arise once, and then evolve. Neither Pasteur, nor any other post-Darwin researcher in this field, denied the age of the earth or the fact of evolution.

February 19, 1626 (a Thursday)

Francesco Redi

On this date, the Italian physician and poet Francesco Redi was born.

Spontaneous generation (abiogenesis), a long-held theory that life springs up from non-living or decaying organic matter, was based on observations of rotting food seemingly producing living organisms. Francesco Redi, a respected philosopher at the court of the Medici Grand Duke in Tuscany, was the first scientist to question the idea of spontaneous generation. By setting up a simple experiment in which decaying meat was placed in three jars, one uncovered, one sealed, and one covered by mesh, allowing air to circulate, he demonstrated that only the open jar which flies could access produced maggots. Thus, decaying meat does not spontaneously produce maggots. Partially due to the simplicity of Redi’s experiment (anyone could reproduce it), people began to doubt spontaneous generation.

It is important to note that what Redi and others demonstrated is that life does not currently spontaneously arise in complex form from nonlife in nature; they did not demonstrate the impossibility of life arising in simple form from nonlife by way of a long and propitious series of chemical steps/selections under conditions that do not exist on Earth today. In particular, they did not show that life cannot arise once, and then evolve. Neither Pasteur, who put to rest the notion of spontaneous generation for microorganisms, nor any other post-Darwin researcher in this field denied the age of planet Earth or the fact of evolution.

December 27, 1822 (a Friday)

Louis Pasteur

On this date, the chemist and microbiologist Louis Pasteur was born in Dole in the Jura region of France.

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 nonliving 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. Likewise, the spontaneous generation hypothesis was proposed by scientists to explain the origin of the “animalcules” observed by Antoni van Leeuwenhoek in his magnifying lenses and had received wide acceptance all over Europe. Although such a concept may seem laughable today, it was consistent with the other widely held cultural and religious beliefs of the time.

It wasn’t until Louis Pasteur that this fallacy was finally disproved. In 1859, the French Academy of Science offered the Alhumbert Prize of 2500 francs to whoever could shed “new light on the question of so-called spontaneous generation”. Young Pasteur’s award winning experiment was a clever variation of earlier experiments performed by John Needham (1713-1781) and Lazzaro Spallanzani (1729-1799). Pasteur filled a long necked flask with meat broth. He then heated the glass neck and bent it into an “S” shape. Air could reach the broth, but gravity acted to trap airborne microorganisms in the curve of the neck. He then boiled the broth. After a time, no microorganisms had formed in the broth. When the flask was tipped so that the broth reached the microorganisms trapped in the neck, the broth quickly became cloudy with microscopic life.

Pasteur filled a flask with medium, heated it to kill all life, and then drew out the neck of the flask into a long S. This prevented microorganisms in the air from entering the flask, yet allowed air to flow freely. If the swan neck was broken, microbes could enter the flask and grow.

Thus, Pasteur disproved spontaneous generation. Furthermore, Pasteur proved that some microorganisms are airborne. “There is no known circumstance in which it can be confirmed that microscopic beings came into the world without germs, without parents similar to themselves,” he concluded in 1864. His experiment also supported germ theory. Germ theory states that specific microscopic organisms are the cause of specific diseases. While Pasteur was not the first to propose germ theory (Girolamo Fracastoro, Agostino Bassi, Friedrich Henle and others had suggested it earlier), he developed it and conducted other experiments that clearly indicated its correctness, thereby managing to convince most of Europe it was true.

Despite what creationists and proponents of “intelligent design” may insist, Pasteur’s research on spontaneous generation did not demonstrate the impossibility of life arising in simple form from nonliving matter under conditions vastly different from those today and by means of a long and propitious series of chemical steps/selections. In particular, he did not show that life cannot arise once, and then evolve. Neither Pasteur, nor any other post-Darwin researcher in this field, denied the age of Earth or the fact of evolution. What Louis Pasteur and the others who denied spontaneous generation did demonstrate is that life does not currently spontaneously (i.e., within a matter of weeks) arise in complex form from nonlife in nature.

Memorable Quote:

One does not ask of one who suffers: What is your country and what is your religion? One merely says: You suffer, this is enough for me: you belong to me and I shall help you.

— quoted in Louis Pasteur, Free Lance of Science (1950) by René Jules Dubos, p. 85