Evidence for evolution

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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

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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.

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Inheritance of Acquired Characteristics

• Lamarcks proposed 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)

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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

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Charles Darwin published On the origin of
species in 1859.

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Charles Darwin (1809-1882)

• Son of a wealthy doctor.
• Dropped out of medical school.
• Studied theology, but was much more interested in
  natural history.
• After college signed on as captains companion on
  The Beagle.

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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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Unique animals on Galapagos include giant
tortoises, marine iguanas, and Darwins finches.
Galapagos Giant Tortoise
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Sharp- beaked Ground Finch
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On voyage Darwin read Lyells Principles of
Geology. Lyell emphasized two major points

• Gradualism Geological features can be
• explained by the slow gradual action of
• processes we see around us every day.
• E.g. wind, waves, rivers.

2. Great age of the Earth the earth is old,
so there has been lots of time for change to
take place.
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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.

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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
  different from those on other continents.
• 4. Many species on oceanic islands are
• found only there (endemic).
• 5. Endemic species on islands closely resemble
  species found on adjacent mainland.

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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.

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Darwin and Wallace

• 1858 Charles Darwin and Alfred Russel Wallace
  jointly proposed natural selection as the primary
  mechanism by which evolution takes place.
• 1859 Origin of Species published

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

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Evidence for Evolution

• Evidence of change in organisms over time
• Living species
• evolution of beak length in 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.

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Evolution of Soapberry Bugs

• In 1926 flat-podded Golden rain tree introduced
  to Florida. Has thin fruits.
• Today soapberry bugs feeding on Golden rain trees
  have much shorter beaks than those living on
  balloon vines.

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Comparison of beak lengths in areas with and
without golden rain trees
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Data from museum specimens documents change in
beak length over time.
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Vestigial organs

• Many organisms possess rudimentary or
  functionless versions of body parts that function
  in close relatives/ancestors
• Cave populations of Mexican tetra fish have eye
  sockets but no eyes.
• Kiwis have tiny, stubby wings
• Boas have tiny remnant hind limbs

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Human vestigial structures

• Coccyx vestigial tailbone at base of spine.
• Arrector pili muscle at base of hair follicles
  makes hair stand up.
• Appendix reduced in size. Used in digestion of
  cellulose in herbivores e.g. rabbits.

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Vestigial developmental trait

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

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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.

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Fossil evidence of evolution

• Clear from fossil evidence that many species (in
  fact almost all that have ever existed) have
  become extinct.
• Equally clear that the faunas of different
  geological eras are very different and that they
  have changed over time.

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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

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Extinct glyptodont (2,000 kg) resembles
modern-day armadillo (2 kg).
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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.

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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.

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Archaeopteryx (oldest known fossil bird) Jurassic
150mya
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Evolution of mammals

• There are numerous excellent fossil series that
  document the transitions from ancestral species
  to later species.
• For example the evolution of mammals from
  synapsids. An extensive series of fossils
  documents the changes in the synapsid lower jaw
  from a jaw made of multiple bones to the modern
  mammals single dentary and the incorporation of
  some synapsid jaw bones into the inner ear.

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Tiktaalik roseae

• Another example is the evolution of the first
  amphibians from lobe finned fishes.
• The transitional fossil Tiktaalik roseae
  possesses an intermediate suites of characters.
• It has fish-like scales, palate and jaws, but an
  amphibian-like mobile neck and head, an ear that
  could hear in air, and the bones in its fins are
  intermediate between those of fish and early
  amphibians such as Acanthostega.

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Tiktaalik roseae 375 mya
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Evidence of common ancestry. Homologous structures

• Homologous structures are those constructed from
  the same basic components which have been
  modified for different purposes.
• E.g. The forelimbs of human, mole, horse, dolphin
  and bat are constructed from the same bones, but
  the bones differ in size and shape and the
  structures made from the bones are used in
  radically different ways.
• Homologous structures make no sense if organisms
  were specially created, but logical if organisms
  share a common ancestor.

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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
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Developmental Homology

• Embryos of diverse array of vertebrates very
  similar in early development

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• Not all similarities due to homology.
• Streamlined shapes of fish and whale not a result
  of common ancestry but convergent evolution. The
  same selection pressures acting on different
  lineages have produced similarly shaped bodies.

FIG 2.12.
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Analagous structures

• Similarly, the wings of butterflies and birds are
  not homologous (because their structural
  components were not derived from a recent common
  ancestor) but perform the same function.
• Such structures are analagous. They carry out the
  same function.

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Molecular Homology

• With few exceptions all organisms use same
  genetic code.
• Genetic flaws shared by species.

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Molecular Homology

• 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.

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Molecular Homology

• Humans share CMT1A repeat with bonobos and
  chimpanzees, but not gorillas, orang-utans or
  other primates.
• Suggests CMT1A derived from common ancestor of
  bonobos, chimps and humans.

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Other evidence for evolution

• Jerry-rigged structures e.g. The Pandas thumb.

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Pandas Thumb

• In Pandas, a wrist bone modified as tool to
  strip bamboo.
• Pandas thumb not very efficient solution to
• Bamboo-stripping problem.
• Natural selection must work with the material
• available.
• Thumb implies pandas not designed,
• but evolved.

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Other evidence for evolution

• Adaptive radiation and clusters of species.
• Many remote islands populated by
• diverse, but closely related species.

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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.

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Adaptive radiation

• Examples Darwins finches on Galapagos Island,
  Drosophila on Hawaiian Islands.

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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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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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If faunas created, why are woodpecker finches,
but not woodpeckers found on the Galapagos?
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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.

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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.

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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.

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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.

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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).

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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.

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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.

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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.

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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.

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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.

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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.
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Evolution of complex structures

• Computer simulations suggest that eyes can evolve
  easily and in nature eyes have evolved
  independently more than 40 times.