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 biology
The 3 main beliefs about Origins
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Creationist view God created man pretty much in
his present form at one time within the last
10,000 years
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Theistic evolution Man has developed over
millions of years from less advanced forms of
life, but God guided this process, including
man's creation.
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Naturalistic Evolution Man has developed over
millions of years from less advanced forms of
life. God had no part in this process.
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Four Factors that limited the development of
theory of evolution
1. Lack of knowledge on age of Earth 2. The
Concept of fixity of species 3. Lack of
scientific method 4. Notion of separate creation
for humans and animals
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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

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Bishop Ussher 1650

• Earth is very young
• (based on Bible)1st Day of creation Sunday 23
  October 4004 BC

http//www.pbs.org/wgbh/evolution/religion/revolut
ion/index.html
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Carolus Linnaeusc. 1735

• Swedish physician and botanist father of
  taxonomy
• He believed that species were permanent
  creations, God creates, Linnaeus arranges
• Wanted to organize the scale of nature

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ion/index.html
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Georges Cuvier (1769-1832)
Founder of Paleontology (the study of fossils)

• Opposed evolution, thought that boundaries
  between fossil layers corresponded to
  catastrophic events such as floods or droughts
• Catastrophism Earth is young

http//www.pbs.org/wgbh/evolution/religion/revolut
ion/index.html
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Natural Theology

• saw the adaptation of organisms to their
  environment as evidence that the creator had
  designed each and every species for a particular
  purpose
• (based on Judeo-Christian culture)

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ion/index.html
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James Hutton

• In 1795 suggested Gradualism, profound change
  is the cumulative product of slow but continuous
  processes

http//www.pbs.org/wgbh/evolution/religion/revolut
ion/index.html
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Charles Lyell (1797-1875)

• Uniformitarianism
• Embellished Huttons gradualism, geological
  processes are so uniform that their rates and
  effects must balance out through time
• Earth is very old

http//www.pbs.org/wgbh/evolution/religion/revolut
ion/index.html
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Jean Baptiste Lamarck(1744-1829)
Published a theory of evolution in 1809 (year
Charles Darwin was born)

• Individuals can evolve
• Believed that evolution responded to an organisms
  felt needs
• modifications acquired during a lifetime can be
  passed on to offspring
• no evidence for this Ex mice tails

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ion/index.html
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DARWIN1809 -1885

• Darwin trained to be a clergyman
• Beetlemania turned him into a naturalist
• Lyell and Hutton made him rethink the age of the
  Earth
• Got a position as the Naturalist on a 5 year
  voyage

http//www.pbs.org/wgbh/evolution/darwin/diary/
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Beagle Voyage (1831-1836)

• Naturalist aboard the Beagle
• Collected plant Animal specimens
• Took Lyells Book on Geology with him
• Visited many places including Galapagos

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500 miles off coast of South America New
Volcanic Islands Organisms migrated to Islands
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• Developed ideas on Evolution after the voyage.
• Didnt recognize what he was seeing
• Finches and Tortoises

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DARWINAfter the Voyage

• Darwin developed his theory of Natural Selection
• What inspired him?
• Hutton - Gradualism
• Lyell - Earth is Old
• Farmers/Animal Breeder - Variation in populations
• Malthus - Populations grow rapidily
• - Not enough resources for all offspring

http//www.pbs.org/wgbh/evolution/darwin/diary/
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All populations have variation
Darwin knew many farmers and animal breeders.
From them and his own research he knew all
individuals in a population are different.
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DARWIN reads Malthus1838
In 1838, Darwin reads for amusement Malthuss
book Population.
In nature, animals and plants produce more
offspring than can survive. This leads to a
struggle for existence.
Darwin see that favourable variations in a
population would tend to be preserved, and
unfavourable ones to be destroyed. He at last
has a theory by which to work.
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Darwin publishes the Origin of Species1865
Didnt publish is ideas for 20 years!!! Why?
Wallace comes up with the idea of Natural
Selection independently of Darwin. Forces Darwin
to finally publish his book on Evolution
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Darwins Five major theories of Evolution

• 1. The nonconstancy of species (species can
  evolve)
• 2. The descent of all organisms from common
  ancestors (branching evolution)
• 3. The gradualness of evolution (evolution takes
  time)
• 4. The multiplication of species (speciation
  formation of new species)
• 5. Natural selection (the mechanism of evolution)

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Darwins Explanatory Model of Natural Selection
Fact - 1

• Every population has such high fertility that its
  size would increase exponentially if not
  constrained. (source Malthus)

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Fact - 2

• The size of populations, except for temporary
  annual fluctuations, remain stable over time.
  (source observation)

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Fact - 3

• The resources available to every species are
  limited (source observation Maltus)
• Inference 1. There is intense competition
  (struggle for existence) among the members of a
  species.

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Fact - 4

• No two individuals of a population are exactly
  the same (source animal breeders taxonomists)
• Inference 2. Individuals of a population differ
  from each other in the probability of survival

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Fact - 5

• Many of the differences among the individuals of
  a population are, at least in part, heritable.
  (source animal breeders)
• Inference 3. Natural selection, continued over
  many generations, results in evolution.

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To sum up

• Populations evolve, not individuals.
• Every species produces vastly more offspring than
  can survive from generation to generation
• All individuals of a population differ
  genetically from each other.
• They are exposed to the adversity of the
  environment, and almost all of them perish or
  fail to reproduce.
• Only a few of them (on average two per set of
  parents) survive and reproduce.
• There survival is not random, but is aided by the
  possession of certain attributes that favor
  survival

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Truth or Misconception?

• Evolution has a plan for us
• Humans are the pinnacle of Evolution
• Species evolve by choice
• Humans have finished evolving
• Natural selection causes changes in an organism
• Changes in your physical character's an
  individuals life will be passed on to your
  offspring

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Truth or Misconception? (cont.)

• Evolution is concerned with the good of the
  individual
• Evolution is concerned with the good of the
  species
• Natural selection picks organisms that are best
  adapted to their environment
• Humans are better adapted than Dolphins
• Survival of the fittest Lions are fitter than
  zebras
• Evolution is the creation of new species
• An Elk with bigger antlers is fitter than the one
  with smaller antlers

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1. Organisms reproduce like organisms 2. In most
species only a small percentage of the offspring
will actually survive to reproduce 3. There are
variations in individuals in a given population
these variations can be passed on. 4. Whether an
individual will survive to breed depend upon the
interaction between the organism, other organisms
the environment. Some variations will be
favorable. These variations will become more
common from one generation to the next. 5.
Given time natural selection will lead to
different groups of organisms (speciation)nn