Theories about the evolution of
organic molecules
Year 11:Biology
 Describe
two scientific
theories relating to the
evolution of the chemicals
of life and discuss their
significance in
understanding the origin of
life
Spontaneous generation
 As
far back as the time of
Aristotle, humans thought that
life spontaneously arises from
non-living matter.
 They
saw maggots appear in
rotting meat
 This
concept of spontaneous
generation was an accepted ‘fact’
and was not scientifically tested
until 1668.
 Francesco
Redi an Italian physician,
demonstrated that maggots in
decaying meat came from eggs laid
by flies
 About
100 years later Lazzaro
Spallanzani showed that the
microorganisms that appeared
in broth came from the air
 However
his experimental
technique was not sufficient to
exclude spontaneous
generation


It was almost another 100 years,
1862, before French scientist Louis
Pasteur convinced people that the
spontaneous generation did not
occur
DIAGRAMS

Pasteur’s work and work of others
such as Virchow established the
statement that ‘all life comes from
pre-existing life’
 This
presumed that first living thing
or things had to arise somewhere,
sometime, somehow