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Evidence for evolution

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Title: Evidence for evolution


1
Evidence for evolution
  • Early 1800s prevailing belief was that organisms
    specially created.
  • Organisms unchanged since their creation
  • Species created independently of each other
  • Earth not old. Usshers estimate for Earths
    creation 4004 BC

2
Lamarck
  • Fact of evolution proposed in late 1700s early
    1800s.
  • Jean Baptiste Lamarck 1809, 1815 proposed all
    species derived by gradual evolution from other
    species.
  • Evolution driven by innate tendency of organisms
    to become more complex.

3
Inheritance of Acquired Characteristics
  • Mechanism of evolution was Inheritance of
    Acquired Characteristics (IAC)
  • IAC suggested that modifications to organisms
    during their life could be passed on to their
    offspring (e.g. giraffe stretching its neck
    during its life passes slightly longer neck to
    offspring)

4
Inheritance of Acquired Characteristics
  • Obviously, Lamarcks ideas about mechanism of
    evolution contradict current biological
    knowledge.
  • Information flows from DNA to phenotype not in
    the reverse direction

5
Charles Darwin published On the origin of
species in 1859.

6
Charles Darwin (1809-1882)
  • Son of a wealthy doctor.
  • Dropped out of medical school.
  • Studied theology, but much more interested in
    natural history.
  • After college signed on as captains companion on
    The Beagle.

7
Voyage of the Beagle
  • Darwin companion for Captain Fitzroy on
  • Voyage of The Beagle (1831-1836).
  • The Beagles mission was to map coast of South
    America, but traveled around the World.
  • Sites visited included Galapagos Islands.
  • Volcanic islands (hence of recent origin)
  • off coast of Ecuador.

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9
Unique animals on Galapagos include giant
tortoises, marine iguanas, and Darwins finches.
Galapagos Giant Tortoise
10
Sharp- beaked Ground Finch
11
On voyage Darwin read Lyells Principles of
Geology. Lyell emphasized two major points
  • Gradualism Geological features can be
  • explained by gradual action of processes we
  • see around us. E.g. wind, waves, rivers.

2. Great age of the Earth
12
What Darwin observed
  • On the voyage Darwin noted many things that were
    puzzling from the point of view of a creationist
    explanation for the diversity of life.

13
What Darwin observed
  • 1. South American fossils resembled living
    animals.
  • 2. Parts of the world with similar climates and
    habitats
  • (e.g. Australia, South America) populated by very
    different organisms.
  • 3. Plants and animals on each continent are
    distinctive.
  • 4. Many species on oceanic islands are
  • found only there (endemic).
  • 5. Endemic species on islands closely resemble
    species on adjacent mainland.

14
What Darwin observed
  • These observations taken together dont make
    sense if organisms are specially created. Why
    should similar habitats in different parts of the
    world have completely different faunas? Why
    should remote islands have unique faunas that
    differ from, but resemble, those on adjacent land
    masses?
  • Together these observations suggested to Darwin
    that species change over time i.e., evolution
    occurs.

15
Darwin and Wallace
  • 1858 Charles Darwin and Alfred Russel Wallace
    jointly proposed natural selection as the
    mechanism of evolution.
  • 1859 Origin of Species published

16
  • Idea of evolution accepted rapidly
  • Lack of understanding of heredity and population
    genetics prevented natural selection being
    accepted as mechanism until 1930s.
  • Modern Synthesis of population genetics and
    natural selection to explain gradual evolution,
    speciation, and macroevolution.

17
Evidence for Evolution
  • Evidence of change in organisms over time
  • Living species
  • evolution of beak length is soapberry bugs.
  • Soapberry bugs use long beak to penetrate seeds
    in fruits and eat them.
  • Native host plant is balloon vine which has thick
    fruits.

18
Evolution of Soapberry Bugs
  • In 1926 the flat-podded golden rain tree was
    introduced into Florida. Has thin fruits.
  • Today soapberry bugs feeding on golden rain trees
    have much shorter beaks than those living on
    balloon vines.

19
Comparison of beak lengths in areas with and
without golden rain trees
20
Data from museum specimens documents change in
beak length over time.
21
Fossil evidence of evolution
  • It is clear from fossil evidence that many (in
    fact almost all that have ever existed) species
    have become extinct.
  • The presence of vast numbers of fossil species
    that show clear patterns of change within
    lineages over time is clearly strong evidence
    that life on earth has changed dramatically over
    time.

22
Fossil evidence of evolution
  • Law of Succession Fossil and living organisms in
    same area related to each other and differ from
    organisms in other areas.
  • E.g. Australia filled with marsupials, fossils
    are of similar marsupial forms.
  • South America contains both fossil and living
    armadillos

23
Extinct glyptodont (2,000 kg) resembles
modern-day armadillo (2 kg).
24
Fossil evidence of evolution
  • Transitional forms
  • If fossil organisms ancestral to modern organisms
    then there should be transitional fossils that
    show characteristics intermediate between the
    older and more recent groups.

25
Archaeopteryx
  • Archaeopteryx the oldest known fossil bird (name
    means ancient wing) has mix of reptilian and
    avian features.
  • Reptilian long tail, teeth, long clawed fingers
  • Avian feathers, ribs with uncinate processes,
    avian shoulder girdle.

26
Archaeopteryx (oldest known fossil bird) Jurassic
180mya
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28
Anatomical evidence of evolution Vestigial organs
  • Many organisms possess rudimentary or
    functionless versions of body parts that function
    in close relatives/ancestors. These are known as
    vestigial structures.
  • Cave populations of Mexican tetra fish have eye
    sockets but no eyes.
  • Kiwis (flightless New Zealand birds) have tiny,
    stubby wings
  • Boas have tiny remnant hind limbs

29
Human vestigial structures
  • Coccyx vestigial tailbone at base of spine.
  • Appendix Primates that specialize on plant diets
    have a large cecum, which contains bacteria that
    break down cellulose. The human appendix is a
    reduced relic of the ancestral cecum.
  • Arrector pili muscle these muscles erect
    individual hairs, which is useful if you have a
    fur coat (it helps keeps you warm by trapping air
    under the fur) but serves no purpose in humans.

30
  • Arrector pili muscle at base of hair follicles
  • makes hair stand up.

31
Vestigial developmental traits
  • Adult chickens three bones in forefoot (wing),
    four in hindfoot.
  • However, digit 5 appears briefly during embryonic
    development before disappearing.

32
Molecular vestigial traits
  • Human genome contains large numbers of
    pseudogenes that do not code for functional RNA
    or proteins.
  • E.g. several pseudogenes of hemoglobin. May be
    as many as 6,000 pseudogenes in human genome.

33
Molecular vestigial traits
  • Pseudogenes are versions of genes that have been
    turned off. In most cases this probably occurred
    when stop codons (which stop transcription of the
    gene) were inserted into genes as a result of a
    mutation.

34
Anatomical evidence of evolution Atavistic
structures
  • Atavistic structures are throwbacks the return
    of structures once present in ancestors.
  • For example, in modern horses (which usually have
    only one toe) occasionally a foal is born that
    has extra toes (a characteristic of ancestral
    horses).
  • Such atavistic structures are the result of
    developmental errors that probably result from
    remnants of genetic code that are normally turned
    off being turned back on.

35
Evidence of common ancestry. Homologous structures
  • Homologous structures are constructed from the
    same basic components which were derived from a
    common ancestor.
  • For example, the forelimbs of humans, moles,
    horses, dolphins and bats constructed from same
    bones, but used in radically different ways.
  • This makes no sense if organisms were specially
    created, but does if these organisms share a
    common ancestor.

36
Homologous structures (i.e. derived from a common
ancestor). Even though the forelimbs have
evolved to carry out very different tasks they
are all constructed from the same bones.
FIG 2.11
37
Developmental Homology
  • Embryos of diverse array of vertebrates are very
    similar in early development.
  • Across widely different groups general features
    are preserved such as a post-anal tail, gills and
    limbs snake embryos initially develop the
    beginning of limbs that later disappear

38
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39
Similarity not always due to homology
  • Not all similarities due to homology.
  • Streamlined shapes of fish and whale not a result
    of common ancestry

FIG 2.12.
40
Molecular Homology
  • With few exceptions all organisms use same
    genetic code.

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42
Molecular homology
  • Theoretically an infinite number of possible
    genetic codes could be developed and it might be
    advantageous for humans to have a unique one.
  • If we did the HIV virus for example could not
    hijack our cells to make copies of itself.
  • The fact that all organisms use the same code
    argues strongly for common ancestry and that the
    code is homologous.

43
Molecular Homology genetic flaws shared across
species
  • Chromosome 17 in humans PMP22 gene has duplicate
    sequence of DNA (CMT1A repeat) on either side of
    it.
  • Result of duplication and insertion of DNA.
  • Occasionally causes inaccurate crossing over
    during meiosis.

44
Molecular Homology genetic flaws shared across
species
  • Humans share this CMT1A repeat with bonobos and
    chimpanzees, but not with gorillas, orang-utans
    or other primates.
  • Suggests CMT1A repeat was derived from the common
    ancestor of bonobos, chimps and humans.

45
Other evidence for evolution Jerry-rigged
structures
  • Jerry-rigged structures e.g. The Pandas thumb.

46
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47
Pandas Thumb
  • In Giant Pandas, a wrist bone the radial sesamoid
    is modified as tool to strip leaves from bamboo
    stalks.
  • The pandas thumb is not very efficient
    solution to the bamboo-stripping problem.
  • Natural selection must work with the material
  • available.
  • Thumb implies pandas not designed,
  • but evolved.

48
Other evidence for evolution
  • Adaptive radiation and clusters of species.
  • Many remote islands populated by
  • diverse, but closely related species.

49
Adaptive radiation
  • Ancestral colonist arrives on island.
  • Shortage of resident species means many niches
    are unfilled.
  • Ancestral species give rise to many species that
    occupy unfilled niches.

50
Adaptive radiation
  • Examples Darwins finches on Galapagos Island,
    Drosophila on Hawaiian Isalnds.

51
Darwins Finches
  • On Galapagos Islands there are 13 species of
    anatomically very different, but closely related
    species of finch.
  • They differ greatly in beak size and diet having
    evolved very different lifestyles.

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53
Hawaiian Drosophila
  • More than 25 of the worlds 1,250 species of
    Drosophila fruit flies found on Hawaiian Islands.
  • Few insect competitors so Drosophila have
    diversified to fill large number of niches.

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55
If faunas created, why are woodpecker finches,
but not woodpeckers found on the Galapagos?
56
Creationism and Intelligent Design
  • The idea of evolution has been harshly criticized
    by religious fundamentalists since the
    publication of the Origin in 1859.
  • This has been especially true in the U.S.
  • Repeatedly, believers in the literal truth of the
    Bible have attempted to have alternatives to
    evolution (i.e., creationism) taught in the
    public schools and to have the teaching of
    evolution either banned or restricted.

57
Creationism and Intelligent Design
  • The U.S. Supreme Court has prohibited the
    teaching of creationism in public schools as a
    violation of the establishment of religion clause
    of the Constitution.
  • Latest attempt to insert creationism into schools
    is the idea of Intelligent Design.

58
Creationism and Intelligent Design
  • The concept of intelligent design is outlined
    most clearly in Michael Behes book Darwins
    Black Box.
  • The central idea in intelligent design is that
    some structures in the body are so complex that
    they could not possibly have evolved by a gradual
    process of natural selection. These structures
    are said to irreducibly complex.

59
Creationism and Intelligent Design
  • By irreducibly complex Behe means that a
    complex structure cannot be broken down into
    components that are themselves functional and
    that the structure must have come into existence
    in its complete form.

60
Creationism and Intelligent Design
  • If structures are irreducibly complex Behe
    claims that they cannot have evolved. Thus,
    their existence implies they must have been
    created by a designer (i.e. God, although the
    designer is not explicitly referred to as such).

61
Creationism and Intelligent Design
  • Behes main examples are various biochemical
    pathways in the body, the blood clotting system,
    and structures such as the bacterial flagellum.

62
Creationism and Intelligent Design
  • Since the publication of Behes book, it has been
    demonstrated repeatedly that things he has
    claimed to be irreducibly complex are not in fact
    so.
  • E.g. the flagellum in eel sperm lacks several of
    the components found in other flagella, yet the
    flagellum functions well.

63
Creationism and Intelligent Design
  • The blood clotting system in dolphins lacks at
    least one component that the human system has,
    yet it too is functional.
  • In addition, plausible gradual scenarios for the
    evolution of biochemical pathways including the
    Krebs cycle have been documented.

64
Evolution of complex structures
  • The evolution of complex structures, such as the
    eye, appears difficult, but natural selection
    achieves this by the slow accumulation of minor
    improvements from one generation to the next.

65
Evolution of complex structures
  • Each step on the evolutionary pathway from a
    simple light sensing cell to a complex eye
    capable of focusing and producing color vision,
    must be beneficial to the organism that possess
    it and a slight improvement on earlier versions.
  • It is not necessary for a structure to be perfect
    or even very good it just needs to be better than
    the alternatives to be favored by selection.

66
Variation in mollusc eyes from (a) pigment spot
to (b) pigment cup to (c) simple optic cup in
abalone to (d) complex lensed eyes in a marine
snail and octopus.
67
Evolution of complex structures
  • Computer simulations suggest that eyes can evolve
    easily and in nature eyes have evolved
    independently more than 40 times.
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