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

• 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 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 gradual action of processes we
• see around us. E.g. wind, waves, rivers.

2. Great age of the Earth
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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
  distinctive.
• 4. Many species on oceanic islands are
• found only there (endemic).
• 5. Endemic species on islands closely resemble
  species 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
  mechanism of evolution.
• 1859 Origin of Species published

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• 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.

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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.

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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.

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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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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.

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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
180mya
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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

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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.

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

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Vestigial developmental traits

• 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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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.

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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.

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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.

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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 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

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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.
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Molecular Homology

• With few exceptions all organisms use same
  genetic code.

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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.

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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.

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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.

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Other evidence for evolution Jerry-rigged
structures

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

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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.

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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 Isalnds.

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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.