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Darwin

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Title: Darwin


1
Darwin Descent with Modification
  • Ch 22

2
  • The Origin of Species
  • Focused biologists attention on the great
    diversity of organisms

3
  • Darwin made two major points in his book
  • He presented evidence that the many species of
    organisms presently inhabiting the Earth are
    descendants of ancestral species
  • He proposed a mechanism for the evolutionary
    process, natural selection

4
  • Concept 22.1 The Darwinian revolution challenged
    traditional views of a young Earth inhabited by
    unchanging species
  • In order to understand why Darwins ideas were
    revolutionary
  • We need to examine his views in the context of
    other Western ideas about Earth and its life

5
  • The historical context of Darwins life and ideas

6
The Scale of Nature and Classification of Species
  • The Greek philosopher Aristotle
  • Viewed species as fixed and unchanging
  • The Old Testament of the Bible
  • Holds that species were individually designed by
    God and therefore perfect
  • Carolus Linnaeus
  • Interpreted organismal adaptations as evidence
    that the Creator had designed each species for a
    specific purpose
  • Was a founder of taxonomy, classifying lifes
    diversity for the greater glory of God

7
Fossils, Cuvier, and Catastrophism
  • The study of fossils
  • Helped to lay the groundwork for Darwins ideas
  • Fossils are remains or traces of organisms from
    the past
  • Usually found in sedimentary rock, which appears
    in layers or strata

8
  • Paleontology, the study of fossils
  • Was largely developed by French scientist Georges
    Cuvier
  • Cuvier opposed the idea of gradual evolutionary
    change
  • And instead advocated catastrophism, speculating
    that each boundary between strata represents a
    catastrophe

9
Theories of Gradualism
  • Gradualism
  • Is the idea that profound change can take place
    through the cumulative effect of slow but
    continuous processes

10
  • Geologists Hutton and Lyell
  • Perceived that changes in Earths surface can
    result from slow continuous actions still
    operating today
  • Exerted a strong influence on Darwins thinking
  • Lyell uniformitarianism same geologic
    processes are operating today as in the past and
    at same rate

11
Lamarcks Theory of Evolution
  • Lamarck hypothesized that species evolve
  • Through use and disuse and the inheritance of
    acquired traits
  • But the mechanisms he proposed are unsupported by
    evidence

12
  • Concept 22.2 In The Origin of Species, Darwin
    proposed that species change through natural
    selection
  • As the 19th century dawned
  • It was generally believed that species had
    remained unchanged since their creation, but a
    major change would challenge this thinking

13
  • Darwins interest in the geographic distribution
    of species
  • Was kindled by the Beagles stop at the Galápagos
    Islands near the equator west of South America

14
Darwins Focus on Adaptation
  • As Darwin reassessed all that he had observed
    during the voyage of the Beagle
  • He began to perceive adaptation to the
    environment and the origin of new species as
    closely related processes

15
  • From studies made years after Darwins voyage
  • Biologists have concluded that this is indeed
    what happened to the Galápagos finches

16
Summary of Natural Selection
  • Natural selection is differential success in
    reproduction
  • That results from the interaction between
    individuals that vary in heritable traits and
    their environment
  • If an environment changes over time
  • Natural selection may result in adaptation to
    these new conditions

17
  • Natural selection can produce an increase over
    time
  • In the adaptation of organisms to their
    environment

18
  • In 1844, Darwin wrote a long essay on the origin
    of species and natural selection
  • But he was reluctant to introduce his theory
    publicly, anticipating the uproar it would cause
  • In June 1858 Darwin received a manuscript from
    Alfred Russell Wallace
  • Who had developed a theory of natural selection
    similar to Darwins
  • Darwin quickly finished The Origin of Species
  • And published it the next year

19
Descent with Modification
  • The phrase descent with modification
  • Summarized Darwins perception of the unity of
    life
  • States that all organisms are related through
    descent from an ancestor that lived in the remote
    past

20
  • In the Darwinian view, the history of life is
    like a tree
  • With multiple branchings from a common trunk to
    the tips of the youngest twigs that represent the
    diversity of living organisms

21
Natural Selection and Adaptation
  • Evolutionary biologist Ernst Mayr
  • Has dissected the logic of Darwins theory into
    three inferences based on five observations

22
  • Observation 1 For any species, population sizes
    would increase exponentially
  • If all individuals that are born reproduced
    successfully

23
  • Observation 2 Nonetheless, populations tend to
    be stable in size
  • Except for seasonal fluctuations
  • Observation 3 Resources are limited
  • Inference 1 Production of more individuals than
    the environment can support
  • Leads to a struggle for existence among
    individuals of a population, with only a fraction
    of their offspring surviving

24
  • Observation 4 Members of a population vary
    extensively in their characteristics
  • No two individuals are exactly alike

25
  • Observation 5 Much of this variation is
    heritable
  • Inference 2 Survival depends in part on
    inherited traits
  • Individuals whose inherited traits give them a
    high probability of surviving and reproducing are
    likely to leave more offspring than other
    individuals

26
  • Inference 3 This unequal ability of individuals
    to survive and reproduce
  • Will lead to a gradual change in a population,
    with favorable characteristics accumulating over
    generations

27
Differential Predation in Guppy Populations
  • Researchers have observed natural selection
  • Leading to adaptive evolution in guppy populations

28
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29
The Evolution of Drug-Resistance
  • In humans, the use of drugs
  • Selects for pathogens that through chance
    mutations are resistant to the drugs effects
  • Natural selection is a cause of adaptive
    evolution
  • Drugs do not create resistant pathogens, they
    select for resistant individuals already in the
    population

30
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31
The Fossil Record
  • The succession of forms observed in the fossil
    record
  • Is consistent with other inferences about the
    major branches of descent in the tree of life

32
Anatomical Homologies
  • Homologous structures between organisms
  • Are anatomical resemblances that represent
    variations on a structural theme that was present
    in a common ancestor

33
  • Comparative embryology
  • Reveals additional anatomical homologies not
    visible in adult organisms

34
  • Vestigial organs
  • Are some of the most intriguing homologous
    structures
  • Are remnants of structures that served important
    functions in the organisms ancestors

35
  • Analogous structures
  • Similar solution to similar problems but doesnt
    show relatedness

36
Molecular Homologies
  • Biologists also observe homologies among
    organisms at the molecular level
  • Such as genes that are shared among organisms
    inherited from a common ancestor

37
  • Anatomical resemblances among species
  • Are generally reflected in their molecules, their
    genes, and their gene products

38
Homologies and the Tree of Life
  • The Darwinian concept of an evolutionary tree of
    life
  • Can explain the homologies that researchers have
    observed

39
Biogeography
  • Darwins observations of the geographic
    distribution of species, biogeography
  • Formed an important part of his theory of
    evolution
  • Some similar mammals that have adapted to similar
    environments
  • Have evolved independently from different
    ancestors

40
Summarizing
  • Evolution is a change in species over time
  • Heritable variations exist within a population
  • These variations can result in a differential
    reproductive success
  • Over generations, this can result in changes in
    the genetic composition of the population
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