Origin of Life

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Francesco Redi

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Did Redi Use the Scientific Method?

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The Scientific Method

Observation

Hypothesis

Experiment

Accept, Reject, or Modify hypothesis

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Step 1 - Observation

There were flies around meat carcasses at the Butcher shop.

Where do the flies come from?

Does rotting meat turn into or produce rotting flies?

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Step 2 - Hypothesis

Rotten meat does not turn into flies. Only flies can make more flies.

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Step 3 - Testing

Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same.

Control group — These jars of meat were set out without lids so the meat would be exposed to whatever it might be in the butcher shop.

Experimental group(s) — One group of jars were sealed with lids, and another group of jars had gauze placed over them.

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Step 4 - Data

Presence or absence of flies and maggots observed in each jar was recorded.

Control group – flies entered, laid eggs, & maggots emerged

Gauze covered – flies on gauze, but not in jar

Sealed jars – No maggots or flies on the meat

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Step 5 - Conclusion

Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms.

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Disproving Spontaneous Generation of Microbes

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Anton van Leeuwenhoek (1674)

Leeuwenhoek began making and looking through simple microscopes

He often made a new microscope for each specimen

He examined water and visualized tiny animals, fungi, algae, and single celled protozoa; “animalcules”

By end of 19th century, these organisms were called microbes