Spontaneous Generation

The rise of the Experimental method

Aristotle (384 BC – 322 BC)

Greek philosopher, student of Plato and teacher of Alexander the Great.

His writings in the natural and physical sciences formed the basis of scientific thought for nearly 2,000 years).

His writings also influenced the theological thinking in the Islamic, Jewish and Christian theologies.

Only about a third of his writings have survived.

He applied logic to his observations, but did not use experimentation of measurement.

Spontaneous Generation Is the idea that living

things can arise from non-living material.

Or, living things of one species can arise from different species.

According to Aristotle living things came from non-living things because the nonliving material contained “vital heat”.

Clams and scallops formed in sand, oysters in slime and barnacles and limpets in rocks.

Note the Scallop, the blue dots are its “eyes”!

Beliefs

Barnacle Geese came from Barnacles.

Seeds and straw turned into mice.

Rotting meat turned into flies.

Shakespeare – snakes and crocodiles forming from the mud of the Nile.

Tapeworms arise from the bodies of their hosts.

A Barnacle goose (Branta leucopsis)

Disproving Spontaneous generation

1668 Francisco Redi challenged the idea that rotting meat produced maggots.

He placed meat in sealed, gauze covered and open containers.

He observed maggots in the open and parially opened containers, but no maggots on the sealed container, though there were some on the mesh.

This experiment had great influence throughout Europe.

John Needham - 1748 The experiments

consisted of briefly boiling a broth mixture.

The mixture was then cooled in an open container to room temperature.

Later, the flasks would be sealed, and microbes would grow a few days later.

Those experiments seemed to show that there was a life force that produced spontaneous generation.

Lazzaro Spallanzi - 1768

Modified Spallanzani’s experiment.

Boiled the broth for an hour.

Partially evacuated the jars and sealed the vessels right after boiling.

No growth was observed.

Some felt that air was necessary for spontaneous generation to occur.

Louis Pasteur - 1859

He boiled a meat broth in a flask that had a long neck that curved downward, like a goose.

The bend in the neck prevented falling particles from reaching the broth, while still allowing the free flow of air.

The flask remained free of growth for an extended period. (over a year!)

When the flask was turned so that particles could fall down the bends, the broth quickly became clouded.