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7.1 Darwin

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7.1 Darwin s Theory Key ideas What important observations did Darwin make on his voyage? How did Darwin account for the diversity of species and the differences ... – PowerPoint PPT presentation

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Title: 7.1 Darwin


1
7.1 Darwins Theory
2
Key ideas
  • What important observations did Darwin make on
    his voyage?
  • How did Darwin account for the diversity of
    species and the differences between similar
    species?
  • How does natural selection lead to evolution?

3
Darwins Observations
  • December 1831, Charles Darwin set sail from
    England on a five year trip around the world.
  • He observed plants and animals he had never seen
    before.
  • This observation led him to develop the theory of
    evolution by natural selection.

4
  • Darwins observations included
  • Diversity of organisms
  • Species a group of similar organisms that can
    mate with each other and produce fertile
    offspring
  • Remains of ancient organisms (fossils)
  • Fossil preserved remains or traces of an
    organism that lived in the past
  • Characteristics of organisms on the Galapagos
    Islands

5
Examples of different species.
6
Fossils
7
Comparisons to South American Organisms
  • How are these iguanas different?

8
Galapagos Organisms
  • Darwins drawings
  • Identify some specific differences in these
    finches beaks.
  • These finches live in different islands.

9
Adaptations
  • Def a trait that helps an organism survive and
    reproduce in its environment.
  • Ex milkweed poisonous or have a bad taste
    avoid being eaten
  • Ex some plants have bright colored flowers
    attract insects

10
Evolution
  • Darwin reasoned that plants or animals that
    arrived on the GI faced environmental factors
    that were different from those on the mainland.
  • Darwin hypothesized that the species gradually
    changed (evolution) over many generations and
    became better adapted to the new environments.

11
Scientific theory
  • Scienfic theory A well-tested concept that
    explains a wide range of observations
  • Darwin concluded that organisms on the GI had
    changed over time, but did not know HOW the
    changes had happened.

12
Selective Breeding
  • Humans have used selective breeding to produce
    sheep and pigeons that fit certain criteria.
  • Darwin thought that a process similar to
    selective breeding might happen in nature.. But
    what process would push this selective breeding
    in nature?

13
Meet the Supercow ? at 330
14
Natural Selection
  • Darwin proposed that evolution occurs in nature
    through natural selection ( individuals that are
    better adapted to their environment are more
    likely to survive and reproduce than other
    members of the same species) in the book called,
    On the Origin of Species by Natural Selection.

15
  • Overproduction Malthus pointed out that
    sometimes the food supply is not large enough to
    feed all the offspring of certain organisms-
    insects, humans, etc.
  • Darwin knew that overproduction occurs in many
    species.
  • Why dont all the offspring survive?

16
  • Genetic Variations a difference between
    individuals of the same species
  • Certain insects may be able to eat foods that
    others might avoid
  • This characteristic gives the insects an
    advantage over others.

17
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18
  • Competetion since food and other resources are
    limited, the members of a species must compete
    with each other to survive.
  • Selection some variations make individuals
    better adapted to their environment making them
    more likely to survive and reproduce

19
  • Selection contd Darwin proposed that, over a
    long time, natural selection can lead to change.
    Helpful variations may gradually accumulate in a
    species, while unfavorable ones may disappear.

20
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21
  • Environmental factors - factors in the
    environment can affect an organismss ability to
    survive.
  • Genes and natural selection like environmental
    factors, genetic variation contributes to
    evolution. Without variations, all members of a
    species would have the same traits.

22
Why the big eyes??
23
NOT EVOLUTION human manipulation.
24
  • Darwin could not explain what caused variations
    or how they were passed on.
  • Scientists later learned that variations can
    result from mutation and the shuffling of alleles
    during meiosis. Genes are passed from parents to
    offspring.
  • Because of this, only traits that are inherited,
    or controlled by genes, can be acted upon by
    natural selection
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