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Abiogenesis & spontaneous generation

Content objective:

What are we learning and why are we learning this? Content, procedures, or skills.

Vocabulary objective

Tier II: High frequency words used across content areas. Key to understanding directions & relationships, and for making inferences.

Tier III: Low frequency, domain specific terms.

Building on what we already know

Make connections to prior knowledge. This is where we build from.


How did the very first life on Earth begin? That’s the subject of abiogenesis.

Once life began, how did it change over time? That’s the subject of evolution.

Here we will focus on abiogenesis.

But first, I’d like to take a moment to address an issue students often ask me about. Many students have said that if they accept a religion, they then must reject science and evolution. Or if they accept science and the existence of evolution, then they have to reject religion.

When this occurs, some students experience distress when learning about scientific topics such as evolution, the Big Bang (creation of our universe billions of years ago), or nuclear chemistry: dating of the Earth’s layers, or fossils within them, is done with radioactive elements. This shows that our world is billions of years old.

However, most religions find science and evolution compatible. See Voices for Evolution, from the National Center for Science Education. Many religious groups teach that evolution is compatible with religious beliefs. These groups include the Catholic Church, many Protestant Christian groups, Jewish, Unitarian Universalists, and more.

Voices for Evolution, National Center for Science Education and updates, such as Rabbinical Assembly adds its voice for evolution

Also see The Clergy Letter Project – an endeavor signed by almost 14,000 Christian priests, bishops and ministers, and hundreds of Jewish rabbis, Unitarian clergy and Buddhist clergy.

Spontaneous Generation

{The following is adapted from an unattributed PowerPoint I found on many websites. If you know the author please let me know.}

The first ideas about abiogenesis were not scientific. For much of history, people believed that animals could come from non-living sources. Some people thought that:
– frogs developed from falling drops of rain
– mice developed from sweaty underwear
– flies developed from decaying meat

This idea was known as “spontaneous generation.” There was no proof. In the past, people believed what they were told by authorities such as the Church, or the ancient Greek philosopher Aristotle. While Aristotle and others did develop some meaningful scientific ideas, their ideas on the origin of life were incorrect.

Some people thought hat mice could be generated spontaneously from wheat and a sweaty shirt. How?

• The wheat provided the “nutritive power” and the shirt provided the “active principle.”

• active principle = mysterious life-force that allowed spontaneous generation to occur

1668 – Francisco Redi (Italian physician and poet)

He attempted to disprove the theory of Spontaneous Generation.

{  http://michelleburden.weebly.com/cell-history-and-cell-theory.html }

His first conclusions was that “The flesh of dead animals cannot engender worms,
unless the eggs of the living being deposited therein”
• He put dead snakes, eels, and veal in large wide-mouthed vessels.
• He sealed one set with wax, and left the other set open to air.
• Result: Decaying meat was teeming with maggots, sealed meat had no maggots
• Wax sealed vessels failed to produce maggots – because the flies were unable to reach the meat

Redi’s critics said he was wrong because:
• He had too many variables
• There is a lack of access to fresh air air.
• We know that everything needs air, so of course no flies grew
• Therefore you haven’t proven anything.

Today we know that Redi’s conclusion’s were correct, yet his critics did correctly point out that his first experiments contained flaws. Pointing out flaws is part of peer review – an important part of the scientific method. So Redi performed another experiment, taking into account those criticisms.

• He covered the jars with fine mesh, which allows in air, but not flies.
• Results: The flies laid eggs on top of mesh, but not on the meat
• So there were no maggots in the meat.


In 1745, John Needham (English Clergyman) wondered if this would work with micro-organisms.

• Everyone knew that boiling killed organisms.
• Needham prepared various broths and showed that they contained microbes.
• Then he boiled them, and showed that there were no longer any microbes.
• He ensured the stoppers were loose, so that air would not be excluded
• Then, after a few days, microbes had reappeared!
• This seemed to be proof that the microbes had spontaneously generated from the non-living broth ?!


Needham’s conclusions was wrong – because he made an incorrect assumption:

What error in experimental method is shown here?
• Needham’s hypothesis: the microbes MUST HAVE arisen spontaneously from the broth.
• Needham’s assumption: there is no other place that the microbes could have come from.
• Wrong, because the microbes could have come from the air

Spallanzani’s (Italian Naturalist) – 1745

He disagreed with Needham
He pointed out that Needham didn’t seal the jars well enough.
Therefore, the microbes could have come from the air.

Spallanzani refined Needham’s experiment

– Spallanzai boiled the flasks longer, and
– sealed the flasks after boiling by fusing the glass tops shut
– Now they were hermetically sealed (airtight)
– result – no growth in any flask

This is great science. He proved that Needham was wrong, and that life did not “spontaneously generate”. The bacteria had come from the outside air.

But then, Needham criticizes Spallanzani’s experiment. Needham said: you boiled it “too long” and spoiled the “vegetative power” by boiling. (supposedly killed the ability of the broth to give life.)

His assumption was that life can still come from broth – but the broth must not be “damaged” by boiling. {This criticism is really not valid. It’s an attempt to reject something true, by positing extra, ad hoc, assumptions, that are not necessary.}

Spallanzani’s created a second experiment, which addressed these new criticisms.

• He did timed boilings, then left them partially sealed.
• Some were partially sealed, while some were hermetically sealed.
• It was hypothesized that more boiling should lead to less life.
• He left some jars as Needham had (with leaky seals)
• to ensure the supposed “active principle” was not damaged.
• Result? Boiling did not damage broth’s ability to support life.
• Bacteria growth depended on the seal only.

1859 – Louis Pasteur (French chemist)

Entered a contest sponsored by the French Academy of Sciences to prove or disprove spontaneous generation.

* His flask allowed in air, but trapped dust (and microbes)
* He used a swan-necked flask
* boiled the infusion
* No growth occurred, even after many days.
* But what about damaging the “active principle”?

{ image from http://education-portal.com/academy/lesson/louis-pasteur-experiments-contribution-theory.html#lesson }

Pasteur showed that the active principle was NOT damaged
• at any later time, he could tip the flask
• this allowed nutrient broth to contact the dust
• this carried microbes into the broth
• result: bacteria growth!

{ image from https://www.koofers.com/flashcards/mcb-exam-1-6/review }

This squashes the old ideas of spontaneous generation.
So how then did life begin? See Abiogenesis – modern discoveries

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