Overview: Scientific Belief in Spontaneous Generation
Great thinkers in ancient times thought that life arose spontaneously in areas where there wasn’t anything living that they could observe. For example, Aristotle believed that some fish were made from the muddy sediment at the bottoms of rivers and oceans. Before the invention of microscopes, eggs that were too small to be seen by the naked eye looked like part of the grains of sand found in silt. The scientists of the time developed elaborate theories of how maggots were formed from decaying meat, or mice came from dirt and grain.
An Early Series of Experiments
Spontaneous generation, known also as abiogenesis, was the theory believed by most philosophers and scientists of the day, as there was no way to test any alternative ideas. Some of the earliest experiments to challenge abiogenesis were performed during the Italian Renaissance in the 1600s. Redi hypothesized that flies laid eggs on the meat as it decayed and that the meat was nothing more than a source of food for the maggots that hatched. In the first set of experiments he performed, he put pieces of meat in jars, left some of them open , and closed some others. The jars that were open attracted flies, and maggots formed in the meat as it decayed. In the closed jars, meat decayed, but maggots did not form in the decaying meat. Redi concluded that maggots weren’t spontaneously generated in the decaying meat, but came from the eggs laid by flies in the decaying meat.
Scientific Method Contradicts Spontaneous Generation
The experiments that Redi conducted were among the earliest to have an experimental group and a control group. In the experimental group, jars were sealed so that meat decayed in them, and in the control group, jars were unsealed so that the flies could lay eggs on the decaying meat. In a second set of experiments, jars in the experimental group were covered with wire mesh so that air could get through, but flies could not. Careful control of experimental conditions showed most scientists that maggots did not develop through spontaneous generation.
Microscopes and Microorganisms
By the 1700s, many scientists were using early microscopes to study organisms that they hadn’t been able to detect before. They were able to devise experiments that further contradicted earlier ideas of spontaneous generation. For example, scientists were able to show small organisms were already living in what appeared to be lifeless water or broth. They varied the amount of time liquid in laboratory flasks were boiled in order to destroy life.
From Spontaneous Generation to Biogenesis
Scientists such as Louis Pasteur in the late 1800s were able to show that living organisms develop from other living organisms, the concept of biogenesis. Small organisms, such as bacteria found on dust particles, contaminate materials by reproducing more organisms rather than spontaneously generating where no life was found before.
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