The Darwinian View of Life

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Chapter 22

• The Darwinian View of Life

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• Greek philosophers had ideas of evolution
• Plato Aristotle opposed evidence of evolution
• The 1700s were dominated by the Natural Theory
• Linnaeus saw no indication of evolution in his
  taxonomical groupings
• Georges Cuvier developed paleontology
• Cuvier was an opponent of evolution
• proposed the theory of catastrophism

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• Charles Lyell proposed uniformitarianism
• Incorporated Huttons theory of gradualism
• 18th century - naturalists began to suggest
  evolution
• Jean Baptiste Lamarck proposed a comprehensive
  model to explain how life evolved
• 1. Use and disuse
• Greatly influenced Darwins ideas of natural
  selection
• 2. Inheritance of acquired characteristics
• No evidence to support this 2nd hypothesis

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• Key aspects of Lamarck's view of evolution
• 1. evolution is the best explanation of the
  fossil record and diversity of life
• 2. Earth is ancient
• 3. Adaptation to the environment is primary
  product of evolution
• Lamarck published his works in 1809
• The year Charles Darwin was born

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• At 22, Charles Darwin served as ship's surgeon on
  the H.M.S. Beagle, surveying the South American
  coastline
• He was a naturalist as well as an MD
• Darwin collected samples of the flora and fauna
  of South America, noting several important
  points
• different from that of Europe
• temperate species were more similar to tropical
  South American species than to European temperate
  species
• Fossils were different than modern species, but
  most resembled the living organisms of South
  America not Europe
• On the Galapogos, many organisms were unique to
  that particular island system

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• Darwin published On the Origin of Species by
  Means of Natural Selection in 1859
• Based on Lyells Principals of Geology and
  Darwins own observations
• convinced the majority of biologists that
  biological diversity was a product of evolution
• Origin developed 2 main points
• Evolution an explanation for lifes unity and
  diversity
• Natural selection the cause of adaptive
  evolution

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• Darwin focused on the role of natural selection
  in adaptation
• Observation 1 All species have such great
  potential fertility allowing for exponential
  growth in the population if all individuals
  reproduced successfully
• Observation 2 Populations tend to remain stable
  in size (may vary with seasons)
• Observation 3 Environmental resources are
  limited
• Inference 1 Struggle for existence
• Producing more individuals than the environment
  can support leads to a struggle for existence
  where only a fraction of offspring survive

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• Observation 4 Individuals of a population vary
  in their characteristics no two individuals are
  exactly alike
• Observation 5 Much of the variation in the
  population is heritable
• Inference 2 Survival depends on the "hereditary
  constitution" of the individual
• Survival of the fittest
• Inference 3 The unequal ability of individuals
  to survive and reproduce will lead to a gradual
  change in a population over time
• Best fit characteristics accumulate over time

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• Summary of Darwins ideas
• Natural selection is the differential success in
  reproduction, its product is adaptation of
  organisms to their environment
• Natural selection occurs from the interaction
  between the environment and the genetic makeup of
  a population
• The product of natural selection is the
  adaptation of a population to its environment
• Genetic variation is the "substrate" for natural
  selection

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• Thomas Malthus contended human suffering was
  directly related to overpopulation
• Darwin concluded that any population had the
  capacity to overproduce
• Natural selection is the result of differential
  reproductive success
• environmental factors filter heritable variations
  favoring some more than others
• Both discrete characters and polygenic characters
  can have genetic variation
• Polymorphism

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• The Darwinian view has two main features
• The diverse forms of life have arisen by descent
  with modification for ancestral species
• The mechanism of modification has been natural
  selection working over enormous tracks of time
• A population is the smallest unit that can evolve
• Evolution can only be measured as changes in the
  proportion of traits in an population
• Natural selection can act only on heritable
  traits not acquired characteristics
• Natural selection is situational

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• Evidence of natural selection and evolution
• camouflage
• Insecticide resistant insects
• Antibiotic resistant microorganisms
• Anatomical and molecular homologies
• The fossil record