Historical Background to Darwin's Theory of Evolution

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Historical Background to Darwin's Theory of
Evolution
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Evolution is the core theme of biologyNothing
in biology makes sense except in the light of
evolution Theodosius Dobzhansky
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Plato (427-347 BC)

• Saw variations in plant and animal populations as
  imperfect representations of ideal forms
• Only the perfect forms of organisms were real
  idealism, essentialism philosophy

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Aristotle (384-322 BC) - Platos student

• all living forms could be arranged on a scale of
  increasing complexity scala naturae (scale of
  nature)
• no vacancies and no mobility in this ladder of
  life
• species are fixed, permanent, and do not evolve
  (Stability of Species)

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Natural Theology

• Saw the adaptation of organisms as evidence that
  the creator had designed each and every species
  for a particular purpose (based on
  Judeo-Christian culture (old testament)
• Earth very young, about 6,000 years old
• Created on October 22, 4004 B.C.

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European colonialism leads to discovery that the
number of species is very large. Maybe species
can change after all?
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Carolus Linnaeus Swedish physician and
botanist father of taxonomyHe believed that
species were permanent creations, God creates,
Linnaeus arrangesIronic because Darwin uses
this taxonomy system as a focal point for
evolution
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TAXONOMY

• Taxonomy branch of biology concerned with naming
  and classifying the diverse forms of life
• Two part binomial system of naming according to
  genus and species, and hierarchy for grouping
  species into increasingly general categories
• Canis Lupus Wolf

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Georges Cuvier (1769-1832) Founder of
Paleontology (the study of fossils)Opposed
evolutionThought that boundaries between fossil
layers corresponded to catastrophic events such
as Noahs flood or droughts
Developed the theory of catastrophism
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James Hutton(1726 - 1797) Scottish
GeologistIn 1795 suggested Gradualism,
profound change is the cumulative product of slow
but continuous processesHe looked a present day
processes like erosion by water. Believed
these processes operating over millions of years
could have created the geologic features we see
today. Therefore the Earth was very old
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Charles Lyell (1797-1875) UniformitarianismEm
bellished Huttons gradualism, geological
processes are so uniform that their rates and
effects must balance out through
timeSuggested the Earth was hundreds of
millions of years old.Darwin took only three
books with him on the Beagle.One was Lyells
book Principles of Geology
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Jean Baptiste Lamarck (1744-1829) published a
theory of evolution in 1809 (year Charles Darwin
was born)Believed that evolution responded to
organisms felt needs use and disuse examples
biceps of blacksmith, giraffes neck - inheritance
of acquired characteristics modifications
acquired during a lifetime can be passed on to
offspringno evidence for this Ex mice tails
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DARWIN

• Darwin used 2 ideas from Hutton and Lyell
• If geological changes results from slow
  continuous changes then earth must be older than
  6000 years (natural theologian calculation)
• Very slow and subtle processes persisting over a
  great length of time can cause substantial change

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• In 1831 he left on a 5 year voyage on board the
  Beagle to survey the coast of South America.
• He stopped off in the Galapagos Islands where the
  diversity of tortoises and birds amazed him
• In 1836 he returned to England
• In 1859 published On the Origin of Species
• What ideas influenced Darwin?

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Darwins Finches
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Darwin saw variation within species on the
different Islands. But didnt fully understand
what he saw till he returned to England
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• From Geologists Hutton and Lyell he knew the
  Earth was old.
• The Economist Malthus explained population growth
  to Darwin
• Populations breed rapidly
• But populations dont grow unchecked
• Most organisms in a population die without
  breeding
• From his observations he could see variation
  within species.

We can summarize Darwins theory of Natural
Selection in the following way.
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Darwins Theory of Natural Selection 1.Organisms
reproduce like organisms (themselves) 2.In most
species only a small percentage will actually
survive to reproduce 3.There are variations in
individuals in a given population these traits
can be passed on. (caused by mutations)
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• 4.Whether an individual will survive to breed
  depends upon the interaction between these
  variations the environment.
• Some variations will be favorable.
• These variations will become more common from one
  generation to the next.
• The process is called Natural selection
• Variations that are favorable will help you
• What makes a successful variation? One that makes
  it more likely for you to
• Get food
• Not get eaten
• Have children
• Thermal conservation
• 5. Given time, natural selection will produce
  different groups of organisms (speciation)