"Where do Living Things Come from?"

"Where do Living Things Come from?"

By Mr. TIndle

What is Spontaneous Generation?

• Spontaneous generation is the idea that living things can be produced from non-living things.

• Classic examples of support for spontaneous generation: Flies gathering around a piece of meat or even a mouse in a cabinent/cupboard.

How do we disprove Spontaneous Generation?

This was the question on the minds of many scientists for hundreds of years. It would take that same amount of time in order to perform experiments to give evidence to the contrary on spontaneous generation.

The scientists that would change the theory spontaneous generation forever. Those scientists are Francesco Redi and Louis Pasteur.

Multiple Select

Who were the two most influential scientists that designed experiments to disprove Spontaneous Generation?

• Louis Pasteur

• Francesco Redi

• Francesco Pasteur

• Louis Redi

Redi's Experimental Logic

in the 1600's Redi was out to disprove the theory of spontaneous generation. However, he needed a controlled experiment in order to disprove the theory. In a controlled experiment a scientist carries out a series of tests that are identical in every respect except for one factor. The next slide will get into Redi's experiment

Redi's Experiment

Through this controlled experiment, Redi took the first steps to disproving the theory of Spontaneous Generation. He did this by placing meat in different jars then choosing to either cover the jars, not cover the jars, or cover them with a thin gauze.

Open Ended

Why do you think a controlled experiment was needed in order to help disprove spontaneous generation? Give me your thoughts in the space provided down below.

Redi's Experiment Continued.

Redi noticed that the uncovered jar had maggots developing in the decaying meat, the covered jars had no flies in the meat at all. This experimental setup and logic lead Redi to discovering that flies must lay their eggs on the meat in order to reproduce.

He reasoned this after seeing that the open jar was full of maggots while the covered jars were not.

Pasteur's Experimental Logic

The theory of spontaneous generation was not won with the single contribution of Redi in the 1600's. Again this idea took hundreds of years to finally die out in the scientific community. However, Pasteur came up with another experimental design that would finally tear a hole wide open in spontaneous generation. It only took about 200 more years in the 1800's to finally do it.

Pasteur's Experiment

The father of pasteurization and fermentation, Pasteur devised an experiment to finally put the nail in the spontaneous generation coffin. In another controlled experiment that stretched over years, Pasteur finally killed the conversation around spontaneous generation.

Open Ended

Why do you think microorganisms and bacteria only showed up in the flask after breaking the seal in Pasteur's experiments?

Pasteur's Experiment Continued.

Pasteur noticed that the flasks of nutrient borth were undistrubed for long periods of time when the flasks containing the broth were never opened. In fact, for over a year, the flasks that were closed and contained the broth stayed clear and free of microorganisms.

However, when Pasteur broke the necks off of other flask he would start to see a cloudy texture develop in the broth signalling bacteria growth. This experiment and Pasteur's background lead him to conclude that new bacteria only arise from existing bacteria.

Conclusion on Spontaneous generation

Evidence was provided by multiple scientists over hundreds of years to disprove the theory of spontaneous generation. We can now look back at this theory as a relic of the past, a byproduct of a weaker understanding of the scientific world. Now we understand spontaneous generation to be wrong in favor of biogenesis.

Open Ended

Why do you think it took so long for biogenesis to replace spontaneous generation in the scientific world?