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Darwin & Evolution by Natural Selection Warbler finch Ground finches Tree finches Cactus eater Insect eaters Seed eaters Bud eater 2006-2007 – PowerPoint PPT presentation

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Title: Darwin

Darwin Evolution by Natural Selection
Charles Darwin
  • Proposed a way how evolution works
  • How did creatures change over time?
  • by natural selection
  • Collected a lot of evidence to support his ideas
  • 1809-1882
  • British naturalist

Voyage of the HMS Beagle
  • Invited to travel around the world
  • 1831-1836 (22 years old!)
  • makes many observations of nature
  • main mission of the Beagle was to chart South
    American coastline

Voyage of the HMS Beagle
  • Stopped in Galapagos Islands
  • 500 miles off coast of Ecuador

Most of animals on the Galápagos live nowhere
else in world, but they look like species living
on South American mainland.
Darwin foundmany unique species
Many of Darwins observations made him wonder
Darwin foundclues in the fossils
Darwin found Evidence that creatures have
changed over time
Darwin found Different shells on tortoises on
different islands
Darwin asked Is there a relationship between the
environment what an animal looks like?
Darwin found birds
  • Darwin found
  • Many different birds on the Galapagos Islands.

He thought he found very different kinds
But Darwin found a lot of finches
  • Darwin was amazed to find out
  • All 14 species of birds were finches

But there is only one species of finch on the
Darwin asked If the Galapagos finches came from
the mainland, why are they so different now?
The finches cinched it!
  • different beaks are inherited variations
  • serve as adaptationsthat help birds compete for
  • these birds survive reproduce
  • pass on the genes for those more fit beaks
  • over time nature selected for different species
    with different beaks
  • Darwin found
  • The differences between species of finches were
    associated with the different food they ate.

Darwin said Ahaaaa! A flock of South American
finches were stranded on the Galapagos
Relationship between species (beaks) food
Darwins finches
  • Darwins conclusions
  • variations in beaks
  • differences in beaks in the original flock
  • adaptations to foods available on islands
  • natural selection for most fit
  • over many generations, the finches were selected
    for specific beaks behaviors
  • offspring inherit successful traits
  • accumulation of winning traitsboth beaks
  • separate into different species

From 1 species to 14 species
natural selection for best survival reproduction
Earlier ideas on Evolution
  • LaMarck
  • evolution by acquired traits
  • creatures developed traits during their lifetime
  • give those traits to their offspring
  • example
  • in reaching higher leaves giraffes stretch their
    necks give the acquired longer neck to
  • not accepted as valid

Darwins view of Evolution
  • Darwin
  • giraffes that already have long necks survive
  • leave more offspring who inherit their long necks
  • variation
  • selection survival
  • reproduction inheritance of more fit traits

Asking Questionsis a good adaptation!
Comparative Anatomy
  • Comparative Anatomy includes Homologous and
    Analogous structures as well as vestigial
  • Comparisons of anatomical features in different
    organisms often provides evidence to support the
    theory of evolution. As Organisms are often
    classed together according to similarities in
    their structures.

Homologous Structures
  • Homologous structure are structures that share a
    common origin but may serve different functions
    in modern species.
  • These structures are evidence that organisms with
    similar structure evolved from a common ancestor.
  • Examples include the forelimbs of a variety of
    mammals. For example, human, cat, whale and bat.
  • These species show the same skeletal elements.
    (humerus, radius and ulna)
  • However these skeletal elements have been
    modified over time to suit the different
    functions suitable for the type of mammal.
  • Homologous structures result from divergent
    evolution meaning their ancestral lines started
    out fairly similar, but evolved along different
    paths, becoming more different over time.

  • Structures that are similar due to evolutionary
  • -forearm bones of humans, birds, porpoises, and
    elephants, are called homologous.
  • Structures that evolve separately to perform a
    similar function are called analogous.
  • -The wings of birds, bats, and insects, for
    example, have different embryological origins but
    are all designed for flight.

Analogous Structures
  • Analogous structures are a contrast to homologous
  • They serve the same function between organisms
    but are different in internal anatomy.
  • Such as the wings of birds and butterflies.
  • These structures are of no use in classifying
    organisms or in working out their evolutionary
    relationships with each other.

Vestigial Organs
  • Vestigial organs provide further evidence for
    evolutionary change.
  • These organs are usually dwarfed and useless to
    the organism.
  • Examples of these include
  • The human appendix which is useless in humans,
    but in other mammals it is necessary for
    digestion of high cellulose diet.
  • The human external ear muscles.
  • The tail bone.
  • Wisdom teeth.
  • Some snakes have skeletal limbs.
  • Even though organisms have these organs there is
    no significant disadvantage to the organism.

  • Embryology of organisms can be used to
    demonstrate the existence and even degree of
    relatedness of organisms.
  • In the early stages of development embryos of
    many organisms look extremely similar.
  • Embryos in mammals, birds, reptiles and fish have
    many body similarities in common
  • As the embryos develop further, the similarities
    gradually disappear.
  • This embryonic resemblances indicated that
    organisms are related by their common ancestors.

Similarities in Embryos
  • The layers of fossils in sedimentary rock shows
    the progression of organisms through time.
  • Homologous structures are structures that are
    similar in appearance but not In function.
  • Analogous structures are structures that are
    similar in function but not in appearance.
  • Vestigial Features are organs and structures that
    still remain in animals, however they serve no
    function or purpose in the organism.
  • Embryology shows the similarities that organisms
    have at a very early stage of development.
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