Biogenesis
vs.
Spontaneous
Generation
Fundamental Questions
1. Where do we come from?
2. How did life start on Earth?
3. What were our ancestors like millions of
years ago?
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Science vs. Society
No one can say with absolute certainty and proof
that they have the answers to these questions.
Religions, cultures, communities and schools
of thought often clash with their answers to these
questions – intense and long-standing debates
arose.
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Why Science?
In a scientific investigation, a method is used :
The Scientific Method.
Hypotheses are proposed, tested, and evaluated.
If the evidence is irrefutable, it is commonly accepted. If
not, it is not. This doesn’t indicate TRUTH, just
ACCEPTANCE.
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Has Science Always Agreed?
The best thing about science is that it can
change based on new discoveries and new
evidence.
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Spontaneous Generation
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 didn’t use the scientific method to
arrive at answers to their questions
Their conclusions were based on untested
observations
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Examples of
Spontaneous
Generation
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Example #1
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 year ’ s crop of
food. However, along with the muddy
soil, large numbers of frogs appeared
that weren’t around in drier times
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Example #1
Conclusion: It was perfectly
obvious to people back then that
muddy soil gave rise to the
frogs
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Example #2
Observation: In many parts of
Europe, medieval farmers stored
grain in barns with thatched roofs
(like Shakespeare’s house). As a roof
aged, it was not uncommon for it to
start leaking. This could lead to
spoiled or moldy grain, and of course
there were lots of mice around.
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Example #2
Conclusion: It was obvious to them
that the mice came from the moldy
grain.
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Example #3
Observation: In the cities centuries
ago, there were no sewers, no garbage
trucks,
no
electricity,
and
no
refrigeration. Sewage flowed down the
streets, and chamber pots and left
over food were thrown out into the
streets each morning. Many cities also
had major rat problems and a disease
called Bubonic plague.
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Example #3
Conclusion: Obviously, all the
sewage and garbage turned into the
rats.
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Example #4
Observation: Since there were no
refrigerators, the mandatory, daily
trip to the butcher shop, especially in
summer, meant battling the flies
around
the
carcasses.
Typically,
carcasses were “hung by their heels,”
and customers selected which chunk the
butcher would carve off for them.
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Example #4
Conclusion: Obviously, the rotting
meat that had been hanging in the sun
all day was the source of the flies.
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Abiogenesis Recipes
Recipe for bees:
Kill a young bull, and bury it in an
upright position so that its horns
protrude from the ground. After a
month, a swarm of bees will fly out
of the corpse.
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Abiogenesis Recipes
Recipe for mice:
Place a dirty shirt or some rags in an
open pot or barrel containing a few
grains of wheat or some wheat bran, and
in 21 days, mice will appear. There will
be adult males and females present, and
they will be capable of mating and
reproducing more mice.
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Biogenesis says that in nature, life comes from
previously existing life of its own kind. Every single
science experiment ever done in Biology suggests this
to be true. But in the past, in fact as late as the 1700s,
the dominant theory was abiogenesis, or
spontaneous generation.
Use your own device to find the
meaning of the phrase
“spontaneous generation.” Fill
in the section in your note templates.
Spontaneous Generation
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 didn’t use the scientific method to
arrive at answers to their questions
Their conclusions were based on untested
observations
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Disproving the
idea of
Spontaneous Generation
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
copyright cmassengale
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Theophrastus (371-287 BC)
Paracelsus (1493-1591)
Timeline
DRAW a sketch for each
experiment and write 1
sentence of the conclusion
that can be drawn
Disproving
Spontaneous
Generation
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Francesco Redi
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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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Redi’s 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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Redi’s 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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Redi’s (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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Results of Redi’s Experiments
The results of this experiment
disproved the idea of spontaneous
generation for larger organisms,
but
people
still
thought
microscopic organisms like algae
or bacteria could arise that way.
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Pier Antonio Micheli (1729)
His Nova plantarum genera
(1729) was a major step in
the knowledge of fungi.
He discovered the spores of
mushrooms.
Pier Antonio Micheli (1729)
He observed that when spores
were placed on slices of melon the
same type of fungi were produced
that the spores came from. This
observation led to the discovery
that fungi did not arise from
spontaneous generation.
John Needham (1745)
Showed that microorganisms flourished
in various soups that had been
exposed to the air. Claimed that
there was a “ life force ” present in
the molecules of all inorganic matter,
including air and the oxygen in it, that
could cause spontaneous generation to
occur
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Needham’s Results
Needham’s experiments seemed to
support the idea of spontaneous
generation. People didn’t realize
bacteria were already present in
Needham’s soups. Needham didn’t
boil long enough to kill the microbes
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Needham’s Experiment
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Lazzaro Spallanzani’s (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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Spallanzani’s Results
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Conclusion
Critics said sealed vials did not
allow enough air for organisms to
survive and that prolonged heating
destroyed “life force”
Therefore, spontaneous generation
remained the theory of the time
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The Theory
Finally Changes
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How Do Microbes Arise?
By 1860, the debate had become so heated
that the Paris Academy of Sciences offered a
prize for any experiments that would help
resolve this conflict
The prize was claimed in 1864 by Louis
Pasteur, as he published the results of an
experiment he did to disproved spontaneous
generation in microscopic organisms
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Louis Pasteur (1822-1895)
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Pasteur's Problem
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 Biogenesis
Pasteur’s S-shaped flask kept microbes out
but let air in. Proved microbes only come from
other microbes (life from life) - biogenesis
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Figure 1.3
What about today?
The current acceptance is that life comes from
other life (biogenesis), but the ultimate
question is :
Where did the FIRST
life come from?
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