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Spontaneous Generation
• For over 400 years,
people believed that
life could appear
suddenly from
nonliving material.
People observed
frogs coming out of
mud puddles after
heavy rains and
concluded that frogs
could sprout from
the mud in ponds.
There was even a recipe
written that if you put
grain in a corner and
covered it with rags, it
would make mice!
Spontaneous Generation
• The mistaken
idea that living
things come
from nonliving
sources is called
spontaneous
generation.
Francesco Redi
Spontaneous Generation
• The first scientist
who successfully
attempted to
disprove this
theory was
Francesco Redi
Francesco Redi
• In the mid-1600s,
this Italian doctor
designed one of the
first controlled
experiments to
challenge the theory
of spontaneous
generation.
Redi’s experiment
• Problem: Where do
maggots come from?
• Reid hypothesized that
maggots came from flies.
• To test his hypothesis he
took 3 jars of meat and
placed a piece of meat in
each jar.
Redi’s experiment
• The first jar of meat
had no covering.
• Flies were seen
flying on and near
meat.
• Maggots developed
on the meat.
Redi’s Experiment
• The 2nd jar of meat
had a netting on
top.
• Flies and eggs were
observed flying on
and near the
netting.
• Maggots appeared
on the netting.
Redi’s Experiment
• The 3rd jar of
meat was
sealed.
• No flies could
get near the
meat.
• No maggots
developed.
Redi’s experiment
• What did Redi’s experiment show?
– Maggots do not come from rotting
meat, they come from other flies.
– Redi’s experiment disproved the idea
of Spontaneous Generation.
– Redi’s experiement also showed that
his hypothesis was correct. Life must
come from other life!
Louis Pasteur
Pasteur’s Experiment
• Even after Redi’s work, many people
continued to believe that spontaneous
generation could occur. In the mid1800s, the French chemist named Louis
Pasteur designed a controlled
experiments that finally rejected
spontaneous generation.
Who was Louis Pasteur and what did
he want to research?
• A French chemist and
microbiologist who also disproved
the idea that microbes caused broth
to decay.
• He wanted to find out what caused
milk and wine to spoil.
Louis Pasteur’s Experiment
• Where do microbes come from that cause
broth to decay?
• Believed that microbes came from cells of
organisms in the air, not the air itself.
• Set up an experiment using 3 flasks with
curved necks. (S-shaped jars)
Pasteur’s experiment
• Pasteur filled each
flask with clear
broth.
• The shape of the
neck of the flask
allowed oxygen in,
but kept out
bacteria from the
air.
Pasteur’s experiment
• Pasteur boiled the
broth in one flask
to kill any
bacteria in the
broth. He did not
boil the broth in
the other flask.
Pasteur’s experiment
• In a few days, the
unboiled broth
became cloudy,
showing that new
bacteria were
growing.
• The boiled broth
remained clear.
Pasteur’s experiment
• Pasteur concluded
that bacteria do
not spontaneously
arise from the
broth. New
bacteria appeared
only when living
bacteria were
already present.
Pasteur’s Experiment
• Later, Pasteur took
the curve-necked
flask containing the
broth that had
remained clear and
broke its long neck.
Bacteria from the air
could now enter the
flask. In a few
days, the broth
became cloudy.
Pasteur’s Experiment
• What did Pasteur disprove?
– Spontaneous Generation is false!
– Microbes come from cells of organisms
found in the air, not the air itself.
• What did Pasteur discover?
– The process of Pasteurization
What Did it Prove???
• The experiments of Francesco
Redi and Louis Pasteur helped
to convince people that living
things do not arise from
nonliving material.
The Theory of Biogenesis
• Life comes from life.
• Biogenesis is the process of lifeforms
producing other life forms, ex. a spider
lays eggs, which form into spiders. An
oak tree produces acorns which form
into oak seedling trees.