Who believes in spontaneous generation, not many people any more? Is this because you have been told that the idea of spontaneous generation is untrue? Or perhaps it just doesn’t make sense to you. Keep your reasons in mind as you read or listen to the following.

From the time of Aristotle until the late 17^th century, it was commonly believed that life could spring forth from non-life. The appearance of life was believed to take place without the aid of parent, egg, or seed, and could occur in an almost endless variety of substances and places. This doctrine was called spontaneous generation, and was substantiated by evidence of frogs appearing from mud, flies from rotting fruit and flesh, and other commonly witnessed occurrences by the pre-science world.

Modern biology and life science texts point to Francesco Redi as being an important figure in overturning the doctrine of spontaneous generation. In the late 17^th century Redi was court physician to Ferdinand Medici, Grand Duke of Tuscany. Redi made many observations of plant and animal life, especially observing many infected fruit and oak trees. Redi began to notice that flies visited rotten fruit trees that became wormy. He set about to test the hypothesis that flies were the parents to worms causing the infection. He covered several fruits using fine gauze, leaving others uncovered and observed the fruits for several days. Interestingly, fruits covered with gauze would rot, but not become infected with worms.

Redi, unfortunately, could not show that covering them with gauze could prevent all fruit from becoming infected. The gall infection of the oak continued to occur after covering parts of the tree with gauze. Redi did not reject his hypothesis, however, but instead believed that, contrary to popular opinion, it might be possible for the plants to be producing flies. He stated that worms may come from either the outside, seeking food, gnawing a path into the fruit or from the potency which creates the flower and fruits of living plants, which may also produce the worms.

In addition to these observations of worms and experiments, Redi performed other experiments with rotting meat, in which, after observing flies hatching from pupae, he covered samples of meat with gauze to prevent flies from visiting the meat. By preventing any worms from appearing on the meat, he concluded that worms were the offspring of flies, and not the products of spontaneous generation, something butchers had known for a while. Redi’s experiments questioned the validity of the doctrine of spontaneous generation, which for a while was in doubt.

At about the same time Redi was performing his experiments a Dutch scientist named Leeuwenhoek discovered infusoria. By pouring water over substances such as hay, straw, or pepper, and waiting few hours or days, the water became filled with small living and moving life. This new evidence reaffirmed the doctrine of spontaneous generation, as apparently the life was simple enough that scientists believed it might have formed spontaneously. Scientists believed that given the right conditions, decomposing organic matter could spontaneously reform into simple life.

Spontaneous generation enjoyed popular support for another 200 years, bolstered by philosophical movements predicated on the teachings of Immanuel Kant and others. Kant believed that reason was superior to observation, where the truth could be reasoned to, while observation only provided minimal understanding of nature.

As the teachings of Kant fell from favor and the time of Darwin approached, the idea of spontaneous generation began to fall from popular favor. The religious institutions of the mid 1800’s were bothered by one of the consequences of spontaneous generation. Perhaps Redi put it best when he said "I shall express my belief that the Earth, after having brought forth the first plants and animals at the beginning by order of the Supreme and Omnipotent Creator, has never produced any kinds of plants or animals, either perfect or imperfect; and everything which we know in past or present times that she has produced, came solely from the true seeds of the plants and animals themselves, which thus, through means of their own, preserve their species." Interpretations of spontaneous generation indicated that life could appear without the hand of God, which prompted many scientists to study the doctrine.

Enter French scientist Louis Pasteur, the man credited by modern texts as ending the debate and refuting the doctrine of spontaneous generation. By 1862 when he wrote his first memoirs concerning spontaneous generation, Pasteur was already a popular and prominent scientist due to his discoveries of bacterial fermentation and the process we now know as pasteurization. In these memoirs of 1862 Pasteur recounted much of the history of spontaneous generation, beginning with Redi’s experiments with flies.

It was known that organic or decaying nutrients were needed for the generation of life and also known that heat killed living organisms. In Pasteur’s first experiments simply involved obtaining infusions of yeast, sealing them, and heating them to kill any organisms present. He then waited days and months for the infusions to show signs of life, which they didn’t.

An opponent of Pasteur and proponent of the doctrine of spontaneous generation, named Felix Pouchet performed the same experiments and obtained the same results. Pouchet, however, did not conclude that the doctrine of spontaneous generation was disproved, but rather believed that oxygen was required for the generation of life. The debate between the Pasteur and Pouchet, as well as between proponents and opponents of the doctrine of spontaneous generation raged. Interestingly, subtle attacks on character and intelligence comparable to those of our modern nomination races appeared in several scientists’ memoirs.

Pasteur proceeded to sterilize several infusions in the same manner as before, and then transported half of these flasks to the edge of a glacier at 6000 feet elevation. Here, believing the air to be sterile, he opened the flasks exposing the contents to oxygen. He opened the other flasks at the Museum of Natural history and other locations, including amongst a copse of trees. None of the jars opened at the glacier developed life, while 16 of the flasks opened outdoors showed growth. This indicated to Pasteur that oxygen could not induce spontaneous generation.

Pouchet also performed a series of similar experiments, but when he opened his flasks all of the vessels were subsequently found to contain life. The French Academy was appointed to adjudicate the dispute between Pouchet and Pasteur, but amongst trivial objections Pouchet withdrew from the competition. Pasteur’s status helped cast doubt on Pouchet’s experimental methods, and it was not until years later that it was discovered Pouchet and Pasteur were both incorrect in assuming different infusions would yield the same results. Pouchet, unlike Pasteur, had used infusions of hay rather than yeast.

Pasteur continued to study spontaneous generation, creating an interesting apparatus which allowed air to circulate through the flask after being heated and sterilized. Later experiments involved the introduction into the flask of a cotton filter containing filtered material from unheated air. Pasteur and another scientist named John Tyndall isolated the apparent cause, source, or catalyst of life in the flasks as dust. Unfortunately, other than descriptions of the dust, both scientists only speculated the dust was the seed of the fungi and other life later found in the flask.

Pasteur was elected member of the Acadamy of Sciences in 1862, member of the Academy of Medicine in 1873, and member of the Academie Francaise in 1882. Pouchet and those who still believed in the doctrine of spontaneous generation continued to argue that heat somehow inactivated the oxygen or organic molecules catalyzing the spontaneous generation of life. Opponents of spontaneous generation never directly answered this argument, and Pasteur’s argument gained more acceptance as his renown increased. Today, we accept the doctrine of spontaneous generation as false, but what has convinced you?

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