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Darwin

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Darwin s Theory of Evolution An Australian Aboriginal cave painting Sicilian family Isolating Mechanisms These are barriers lead to reproductive isolation Prevents ... – PowerPoint PPT presentation

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Title: Darwin


1
Darwins Theory of Evolution
2
Who was Charles Darwin?
  • Originally a student of theology
  • Then became a naturalist
  • In 1831, took ship and sailed around the world
  • During his travels, Darwin made numerous
    observations and collected evidence that led him
    to propose a revolutionary hypothesis about the
    way life changes over time

3
Darwins Voyage
4
Darwins Observations
  • Patterns of diversity
  • HUGE amount of diversity among living things
  • Diversity in
  • Traits
  • Offspring production
  • Habitat

5
Darwins Observations
  • Darwin often stopped to collect fossils
  • Preserved remains of ancient organisms
  • Some looked like modern organisms, some clearly
    did not
  • Where did these organisms fit it? Why had so many
    species disappeared?

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The Galapagos Islands
  • Located west of South America
  • Islands were close but had very different
    climates
  • Very fascinated by both the tortoises and the
    finches on these islands
  • Tremendous variety

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The ride back home
  • Darwins return provided a lot of time for
    reflective thought
  • Darwin observed that the characteristics of many
    animals and plants varied noticeably among the
    different islands of the Galápagos.
  • Critical point

12
The ride back home
  • Darwin came up with a possibility
  • Could the animals on the different islands have
    once been the same species?
  • Was that even possible??

13
Ideas that shaped Darwins Ideas
  • Darwin built upon the work of those before him
  • Other scientists built upon his work
  • But
  • Many people were shocked by his ideas and he did
    not receive a lot of initial support

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Evolutionary Roadblocks
  • Ideas in Darwins time
  • Earth was only a few thousand years old
  • Later shown to be billions of years old

16
Evolutionary Roadblocks
  • Ideas in Darwins time
  • Both the planet and its organisms were immutable
    (could not change)
  • Planet is always changingand the life on it

17
Evolutionary Roadblocks
  • Ideas in Darwins time
  • Any strange geologic features were the results of
    infrequent catastrophes that humans rarely
    witnessed
  • Simply not true

18
People who influenced Darwin
  • Scientists had a large influence on Darwin
  • 1. James Hutton
  • 2. Charles Lyell
  • 3. Jean Baptiste Lamarck
  • And an economist
  • 4. Thomas Malthus

19
1. James Hutton
  • Layers of rock are built very slowly
  • Geological forces shaped Earths features
    (mountains and valleys)
  • Took MILLIONS of years
  • Earth is not a few thousand years old

20
2. Charles Lyell
  • Wrote Principles of Geology
  • Stressed that processes that shaped Earth
    millions of years ago are the same processes that
    do so today

21
3. Jean-Baptiste Lamarck
  • Did realize that organisms change over time
  • Published his work the year Darwin was born
    (1809)

22
Lamarcks Proposition
  • Lamarck proposed that by selective use or disuse
    of organs, organisms acquired or lost certain
    traits during their lifetime. These traits could
    then be passed on to their offspring. Over time,
    this process led to change in a species.
  • Had three supporting principles

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A. Tendency Towards Perfection
  • All organisms have a tendency towards perfection
    and complexity
  • Acquired features that helped them live more
    successfully in their environments
  • EX Giraffe has an urge to be tall, and tries to
    do so

26
B. Use and Disuse
  • Organisms could alter the size and shape of their
    organs by using them in new ways
  • If an organ was not used, it would eventually
    disappear
  • EX By trying to be tall, giraffe stretches its
    neck out

27
C. Inheritance of Acquired Traits
  • If an organism altered its body structure during
    its lifetime, then it would pass the new trait to
    its offspring
  • EX If the giraffe stretched its neck and it got
    longer, its babies would have longer necks

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4. Thomas Malthus
  • Looked at population
  • Notice that babies were being born faster than
    people died
  • Malthus reasoned that if the human population
    continued to grow unchecked, sooner or later
    there would be insufficient living space and food
    for everyone.

30
4. Thomas Malthus
  • Looked at population
  • Thought that war, famine, and disease were the
    only things that keep the population in check
  • Darwin realized this was true for every organism,
    and not just humans
  • Most offspring die
  • WHY do some die and some survive?

31
4. Thomas Malthus
  • Food supply is linear
  • Population growth is exponential
  • Problem?

32
Evidence supporting Darwins Ideas
  1. Fossil Evidence
  2. Homologous Structures
  3. Analogous Structures
  4. Vestigial Structures
  5. Comparative Embryology
  6. Biochemical evidence

33
1. Fossil Evidence
  • Fossil evidence shows that living things have
    been evolving on earth for millions of years.
  • Also showed that the geographic distribution of
    organisms lines up with the movement of the
    earths crusts that newer (more modern) forms
    of fossilized organisms are found in the upper
    layers of rock

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2. Homologous Structures
  • Structures that have similar form but different
    functions
  • Bones of our forearm, the front flipper of a
    whale, the wing of a bat legs of a turtle.
  • Could all four limbed animals with backbones have
    descended with modification from a common
    ancestor?

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3. Analogous Structures
  • Structures that have same function but different
    structure/structure
  • Fly and Bird wing
  • Was environment similar so it made sense to have
    this feature?

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4. Vestigial Structures
  • Structures which no longer have a function to the
    organism.
  • Our appendix, hair, coccyx, wisdom teeth
  • These vestiges had a useful function at one time
    but since they are no longer of an adaptive use
    to the organisms, they have become reduced with
    time.

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5. Comparative Embryology
  • Compares structures of developing organisms
    (embryos)
  • Structures found in embryos that have no
    function/use or are not present in adults
  • Early stages of development of many animals with
    backbones are very similar
  • Common ancestor!

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6. Biochemical evidence
  • Not used by Darwin but in use today!
  • Using modern biotechnology, examine the amino
    acids (proteins) and genes (DNA) of organisms.
  • Similar organisms will have more in common. The
    more closely related they are, the more recently
    they descended from a common ancestor

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On the Origin of Species
  • Darwins book
  • Hesitant to publish
  • Alfred Russel Wallaceincentive
  • Never talks about origin of life but how new
    species come to be

50
Darwins Theory of Evolution by Means of natural
selection
  • Variation
  • In a population, there are variations in
    different traits
  • Overpopulation
  • In nature, more organisms are born than can
    survive
  • Competition and Struggle for existence
  • There are not enough resources for all organisms!
  • Certain species have natural advantages

51
Darwins Theory of Evolution by Means of natural
selection
  • 4. Survival of the fittest / Natural Selection
  • Youve got the correct combination of
    advantageous traits (adaptations)?
  • You survive! Try to have babies and pass on those
    stellar genes/traits!
  • You do not have the correct variations and
    adaptations?
  • You die!...thats it.
  • 5. Species change over time
  • Due to natural selection
  • S L O W process
  • New forms / species arise others disappear

52
Natural Selection
53
Natural Selection
54
Comparing Lamarck and Darwin
55
Comparing Lamarck and Darwin
L A M A R C K D A R W I N
56
What was Darwin missing?
  • Darwin published his work in 1836
  • Did not have all pieces to the puzzle
  • What was the source of variation?
  • How are variations passed down from generation to
    generation?

57
What was Darwin missing?
  • Mendel did not publish his work until 1900
  • Watson and Crick did not publish their work until
    1953
  • We can now answer the questions Darwin couldnt
    using genetics, molecular biology, and
    evolutionary theory experiments

58
Sources of Genetic Variation
  1. Mutation may increase, decrease or have no
    effect on the organisms fitness
  2. Gene shuffling during meiosis fertilization,
    genes get shuffled
  3. Crossing over new combinations result during
    prophase I of meiosis

59
Why does it all change?
  • The environment changes!
  • Adaptive radiationthe idea that as organisms
    spread out to a new environment, they will
    acquire changes that allow them to better survive
    in the environment
  • Radiatespread out
  • Adaptchange
  • Best seen with Darwins finches on the Galapagos
    islands

60
Adaptive Radiation
  • Darwins Finches small brown birds
  • Ancestral finches evolved to adapt to open niches
    on the various Galapagos Islands.
  • Some evolved a shorter, fat beak for cracking
    large seeds, some have a smaller, pointier beak
    for opening small seed, while others have a long
    pointed beak for getting into creases in bark for
    insects

61
Adaptive RadiationDarwins Finches
62
Evolutionary paths
  • Based on the environment
  • species can become more different
  • DIVERGENT evolution
  • Results in speciation
  • Leads to homologous structures
  • Idea of adaptive radiation

63
Evolutionary paths
  • Based on the environment
  • species can become more similar
  • CONVERGENT evolution
  • Leads to analogous structures

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Genetic Drift and the Founder Effect
  • Genetic Drift
  • In a small population (isolated one), a
    particular allele may occur more frequently even
    though it doesnt lead to the fitness of the
    population, it is just there
  • Founder Effect
  • Is the change in gene frequency as a result of
    the movement of a small group of a population.

The founder effect CAUSES genetic drift.
66
Sicilian family
An Australian Aboriginal cave painting
67
Isolating Mechanisms
  • These are barriers lead to reproductive isolation
  • Prevents reproductionfurther isolates genes
  • Behavioral isolation
  • Temporal Isolation
  • Geographic isolation

68
A. Behavioral Isolation
  • Different courtship patterns, hibernation or
    estivation patterns, living habits, etc.
  • May totally be different where two populations
    are no longer able to reproduce

69
B. Temporal Isolation
  • Different mating times for species
  • Different pollination times for plants

Wood frogs mate in late March, Leopard frogs mate
in mid April Since both are of the genus Rana,
they can interbreed but do not
Wood Leopard Frogs
70
C. Geographical Isolation
  • Physical barriers separated populations.
  • Over time, they develop two totally different
    gene pools

71
The story of the fruit flies
  • A bunch of flies were minding their own business
    eating a banana
  • A hurricane washed the banana flies onto an
    island
  • Since conditions food are different on the
    island, the flies evolve separate from their
    mainland relatives
  • When some of the flies mix with the mainland
    relatives, they can no longer produce viable
    offspring when they mate.
  • Speciation has occurred!!

72
Extinction
  • 99 of all species that ever inhabited this earth
    have gone extinct!!
  • Mass extinctions
  • Lead open habitats/niches to be filled by
    surviving populations.
  • Leads to evolution of new species
  • Actually considered GOOD for evolution

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Coevolution
  • Two totally unrelated species evolve in response
    to changes in each other over time.
  • Bees dont see red, but do see yellow, blue, and
    UV. Thus, bee-pollinated flowers are mostly
    yellow or blue with UV nectar guides (landing
    patterns) to guide the bee
  • Birds, like hummingbirds have good eyes which can
    see red

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Evolutionary Rates
  • Gradualism evolution is a constant process and
    occurs at a steady rate
  • Punctuated equilibrium- Periods of equilibrium
    followed by rapid periods of change.
  • Change occurs with environmental pressures
  • Species arise abruptly then have long periods of
    little change

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