Spontaneous Generation vs.

Biogenesis

Honors Biology

Aristotle (384 - 322 BC)

• Proposed the theory of Proposed the theory of spontaneous generationspontaneous generation

• Also called Also called abiogenesisabiogenesis• Idea that Idea that living things can living things can

arise from nonlivingarise from nonliving matter matter• Idea lasted almost Idea lasted almost 2000 2000

yearsyears

Early Science

• For centuriesFor centuries, , people basedpeople based their their beliefsbeliefs onon their their interpretations of interpretations of what they what they sawsaw going on in the world going on in the world around them without testing around them without testing their ideastheir ideas

• They They didn’t use the scientific didn’t use the scientific methodmethod to arrive at answers to to arrive at answers to their questionstheir questions

• Their conclusions were based on Their conclusions were based on untested observationsuntested observations

Example of Observations

• Observation:Observation: Every year in the Every year in the spring, the spring, the Nile River floodedNile River flooded areas of Egypt along the river, areas of Egypt along the river, leaving behind nutrient-rich mud leaving behind nutrient-rich mud that enabled the people to grow that enabled the people to grow that year’s crop of food. However, that year’s crop of food. However, along with the muddy soil, along with the muddy soil, large large numbers of frogsnumbers of frogs appeared that appeared that weren’t around in drier timesweren’t around in drier times

Example cont…Conclusion:Conclusion: It was It was perfectly obvious to perfectly obvious to people back then that people back then that muddy soil gave rise to muddy soil gave rise to the frogsthe frogs

John NeedhamBy 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.

John NeedhamAbiogenesis

Microorganisms

Disproving Disproving

Spontaneous Spontaneous

GenerationGeneration

Francesco Redi (1668)Francesco Redi (1668)

• In 1668, In 1668, Francesco Francesco RediRedi, , an Italian an Italian physician, did physician, did an experiment an experiment with with fliesflies and and wide-mouth jars wide-mouth jars containing containing meatmeat

Redi’s ExperimentRedi’s Experiment

• Redi used Redi used open & closed open & closed flasksflasks which which contained meatcontained meat..

• His His hypothesishypothesis was that was that rotten meat does not turn rotten meat does not turn into flies.into flies.

• He He observedobserved these flasksthese flasks to to see in which one(s) maggots see in which one(s) maggots would develop.would develop.

Redi’s (1626-1697) Experiments

Evidence against spontaneous Evidence against spontaneous generation:generation:

1. 1. Unsealed Unsealed – maggots on meat– maggots on meat2. 2. SealedSealed – no maggots on meat – no maggots on meat3. 3. GauzeGauze – few maggots on gauze, none on – few maggots on gauze, none on

meatmeat

Redi’s FindingsRedi’s Findings• He found that if a flask was He found that if a flask was

closedclosed with a lid so with a lid so adult flies adult flies could not get in, no maggotscould not get in, no maggots developed on the rotting meat developed on the rotting meat within.within.

• In a flask In a flask without a lidwithout a lid, , maggots soon were seenmaggots soon were seen in the in the meat because adult flies had meat because adult flies had laid eggs and more laid eggs and more adult flies adult flies soon appeared.soon appeared.

• Did Redi Use the Did Redi Use the Scientific Method?Scientific Method?

Lazzaro Spallanzani’s Lazzaro Spallanzani’s (1765)(1765)

• Boiled soups for Boiled soups for almost an houralmost an hour and and sealed containers by sealed containers by melting the slender melting the slender necks closednecks closed.

• The The soups remained soups remained clearclear..

• Later, he Later, he broke the broke the sealsseals & the & the soups soups became cloudybecame cloudy with with microbes. microbes.

Spallanzani’s ResultsSpallanzani’s Results

ConclusionConclusion• CriticsCritics said sealed vials did said sealed vials did

not allow enough air for not allow enough air for organisms to survive and organisms to survive and that that prolonged heating prolonged heating destroyed “vital force”destroyed “vital force”

• ““Vital force” needed to life Vital force” needed to life to form.to form.

• Therefore, Therefore, spontaneous spontaneous generation remainedgeneration remained the the theory of the timetheory of the time

Needham 1745 Spallanzani 1765

Louis Pasteur (1822-Louis Pasteur (1822-1895)1895)

Pasteur's ExperimentPasteur's Experiment

• Hypothesis:Hypothesis: Microbes come Microbes come from cells of organisms on from cells of organisms on dust particles in the air; not dust particles in the air; not the air itself.the air itself.

• Pasteur put broth into several Pasteur put broth into several special special S-shaped flasksS-shaped flasks

• Each flask was Each flask was boiled and boiled and placed at various locationsplaced at various locations

Pasteur's Experiment - Pasteur's Experiment - Step Step 11

• S-shaped FlaskS-shaped Flask• Filled withFilled with broth broth • The special shaped was The special shaped was • intended to intended to trap any dust trap any dust

particles containing particles containing • bacteriabacteria

Pasteur's Pasteur's Experiment - Experiment - Step 2Step 2

• FlasksFlasks boiledboiled• Microbes KilledMicrobes Killed

Pasteur's Experiment - Pasteur's Experiment - Step 3Step 3

• Flask left at various locationsFlask left at various locations• Did Did not turn cloudynot turn cloudy• Microbes not foundMicrobes not found• Notice the Notice the dustdust that that collected collected

in the neckin the neck of the flask of the flask

Pasteur's Experimental Pasteur's Experimental ResultsResults

The Theory of BiogenesisThe Theory of Biogenesis18641864

• Pasteur’s Pasteur’s S-shaped flask kept S-shaped flask kept microbes out but let air in.microbes out but let air in.

• Proved microbes only come Proved microbes only come from other microbes (life from from other microbes (life from life) - life) - biogenesisbiogenesis

ReviewReview

Mr. Velázquez

Biology

Evidence Pro and ConEvidence Pro and Con

• 1668: 1668: Francisco RediFrancisco Redi filled six jars filled six jars with decaying meat.with decaying meat.

Conditions:Conditions: Results:Results:3 jars covered with fine net - 3 jars covered with fine net - No No

maggotsmaggots3 open jars - Maggots appeared3 open jars - Maggots appeared

From where did the maggots come?From where did the maggots come?What was the purpose of the sealed jars?What was the purpose of the sealed jars?SSpontaneous generation or biogenesis?pontaneous generation or biogenesis?

Evidence Pro and ConEvidence Pro and Con• 1765: 1765: Lazzaro SpallanzaniLazzaro Spallanzani boiled boiled

nutrient solutions in flasks.nutrient solutions in flasks.

Conditions:Conditions: Results:Results:Nutrient broth Nutrient broth placed in flask, placed in flask, heated, then heated, then sealedsealed

No microbial No microbial growthgrowth

SSpontaneous generation or pontaneous generation or biogenesis?biogenesis?

Evidence Pro and ConEvidence Pro and Con• 1861: 1861: Louis PasteurLouis Pasteur demonstrated demonstrated

that microorganisms are present in that microorganisms are present in the air.the air.

Conditions:Conditions: Results:Results:

Nutrient broth Nutrient broth placed in flask, placed in flask, heated, not sealedheated, not sealed

Microbial growthMicrobial growth

Nutrient broth Nutrient broth placed in flask, placed in flask, heated, then sealedheated, then sealed

No microbial No microbial growthgrowth

SSpontaneous generation or biogenesis?pontaneous generation or biogenesis?