Spontaneous Generation
From the seventeenth century, through the Middle Ages, and until the late nineteenth century, it was generally accepted that some organisms originated directly from nonliving matter. Such "spontaneous generation" appeared to start in decaying food, urine, and manure because worms or maggots could be seen hatching there after a few days. It was also believed that animals that lived in mud, such as frogs and salamanders, were generated by the mud in which they lived. Additionally, there were the widely held misconceptions that rats were spontaneously generated in piles of garbage or created from magical recipes. One seventeenth-century recipe even called for the creation of mice from sweaty underwear and wheat husks placed together in a jar for twenty-one days. Although such a concept may seem ludicrous today, it was congruous with other cultural and religious beliefs of the time.
Francesco Redi, an Italian physician, naturalist, and poet, first challenged the idea of spontaneous generation in 1668. At that time, it was widely held that maggots arose spontaneously in rotting meat. Redi did not believe this.He hypothesized that maggots developed from eggs laid by flies. To test his hypothesis, he set out meat in a variety of jars, some open to the air, some sealed completely, and some covered with gauze. As Redi had expected, maggots appeared only in the jars in which the flies could reach the meat and lay their eggs.
Unfortunately, many people who were told or read about these experiments did not believe the results, so if they still wanted to believe in spontaneous generation, they did. Even Redi continued to believe that it occurred under some circumstances and cited the example of grubs developing in oak trees. The invention of the microscope during this time only seemed to further fuel this belief, as microscopy revealed a whole new world of microorganisms that appeared to arise spontaneously.
The debate over spontaneous generation continued for centuries. In the mid-eighteenth century, two other well-documented experiments—one by John Needham, an English naturalist, and the other by Lazzaro Spallanzani, an Italian physiologist—were attempted but were considered by proponents of spontaneous generation to be unpersuasive.
The idea of spontaneous generation was finally laid to rest in 1859 by the French chemist, Louis Pasteur. The French Academy of Sciences sponsored a competition for the greatest experiment that could either prove or disprove spontaneous generation. Pasteur devised a winning experiment where he boiled 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." With this configuration, air could enter the flask, but airborne microorganisms could not, they would settle by gravity in the neck of the flask. As Pasteur had expected, no microorganisms grew. However, when he tilted the flask so that airborne particles could enter, the broth rapidly became cloudy with life. Pasteur had both refuted the theory of spontaneous generation and demonstrated that microorganisms are everywhere, including the air.
Biological Evolution.
Bibliography
Krebs, Robert. Scientific Development and Misconceptions Throughout the Ages. Westport, CT: Greenwood Press, 1999.
Random House Dictionary of Scientists. New York: Random House, 1997.
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