Spontaneous Generation vs. Biogenesis Research Biology

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Spontaneous Generation vs. BiogenesisResearch
Biology
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Aristotle (384 - 322 BC)

• Proposed the theory of spontaneous generation
• Also called abiogenesis
• Idea that living things can arise from nonliving
  matter
• Idea lasted almost 2000 years

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Early Science

• For centuries, people based their beliefs on
  their interpretations of what they saw going on
  in the world around them without testing their
  ideas
• They didnt use the scientific method to arrive
  at answers to their questions
• Their conclusions were based on untested
  observations

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Example of Observations

• Observation Every year in the spring, the Nile
  River flooded areas of Egypt along the river,
  leaving behind nutrient-rich mud that enabled the
  people to grow that years crop of food. However,
  along with the muddy soil, large numbers of frogs
  appeared that werent around in drier times

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Example cont

• Conclusion It was perfectly obvious to people
  back then that muddy soil gave rise to the frogs

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• Disproving
• Spontaneous
• Generation

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Francesco Redi (1668)

• In 1668, Francesco Redi, an Italian physician,
  did an experiment with flies and wide-mouth jars
  containing meat

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Redis Experiment

• Redi used open closed flasks which contained
  meat.
• His hypothesis was that rotten meat does not
  turn into flies.
• He observed these flasks to see in which one(s)
  maggots would develop.

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Redis (1626-1697) Experiments

• Evidence against spontaneous generation 1.
  Unsealed maggots on meat 2. Sealed no
  maggots on meat 3. Gauze few maggots on gauze,
  none on meat

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Redis Findings

• He found that if a flask was closed with a lid so
  adult flies could not get in, no maggots
  developed on the rotting meat within.
• In a flask without a lid, maggots soon were seen
  in the meat because adult flies had laid eggs and
  more adult flies soon appeared.

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• Did Redi Use the Scientific Method?

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John Needham
By 1745 an English scientist used microscopic
observations to support the theory of
abiogenesis. To test the theory he boiled meat
broth for several minutes in a loosely sealed
flask. ( allow to cool down the
flask) Immediately after boiling he saw under
the microscope that the broth had no living
things. After a few days he examined the flask
and found microrganism.
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John Needham Abiogenesis
Microorganisms
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Lazzaro Spallanzanis (1765)

• Boiled soups for almost an hour and sealed
  containers by melting the slender necks closed.
• The soups remained clear.
• Later, he broke the seals the soups became
  cloudy with microbes.

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Spallanzanis Results
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Conclusion

• Critics said sealed vials did not allow enough
  air for organisms to survive and that prolonged
  heating destroyed vital force
• Vital force needed to life to form.
• Therefore, spontaneous generation remained the
  theory of the time

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Needham 1745
Spallanzani 1765
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Louis Pasteur (1822-1895)
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Pasteur's Experiment

• Hypothesis Microbes come from cells of organisms
  on dust particles in the air not the air itself.
• Pasteur put broth into several special S-shaped
  flasks
• Each flask was boiled and placed at various
  locations

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Pasteur's Experiment - Step 1

• S-shaped Flask
• Filled with broth
• The special shaped was
• intended to trap any dust particles containing
• bacteria

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Pasteur's Experiment - Step 2

• Flasks boiled
• Microbes Killed

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Pasteur's Experiment - Step 3

• Flask left at various locations
• Did not turn cloudy
• Microbes not found
• Notice the dust that collected in the neck of the
  flask

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Pasteur's Experimental Results
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The Theory of Biogenesis1864

• Pasteurs S-shaped flask kept microbes out but
  let air in.
• Proved microbes only come from other microbes
  (life from life) biogenesis
• Life come from life

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• Review

Mr. Velázquez Biology
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Evidence Pro and Con

• 1668 Francisco Redi filled six jars with
  decaying meat.
• Conditions Results
• 3 jars covered with fine net - No maggots
• 3 open jars - Maggots appeared
• From where did the maggots come?
• What was the purpose of the sealed jars?
• Spontaneous generation or biogenesis?

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Evidence Pro and Con

• 1765 Lazzaro Spallanzani boiled nutrient
  solutions in flasks.

Conditions Results
Nutrient broth placed in flask, heated, then sealed No microbial growth
Spontaneous generation or biogenesis? Spontaneous generation or biogenesis?
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Evidence Pro and Con

• 1861 Louis Pasteur demonstrated that
  microorganisms are present in the air.

Conditions Results
Nutrient broth placed in flask, heated, neck broken Microbial growth
Nutrient broth placed in flask, heated, then neck not broken. No microbial growth
Spontaneous generation or biogenesis? Spontaneous generation or biogenesis?