Evolution and Natural Selection

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Evolution and Natural Selection

• Wilson/Young/Fairbanks

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Darwin The Theory of Natural Selection

• Before Charles Darwin changed the face of
  science, most of the world thought Earth was only
  6,000 years old and organisms were unchanging.
• Gradual change over time was a foreign concept
  years away from being accepted.
• HMS Beagle
• 1831 Darwin joined the expedition to survey
  South America.
• His job was to collect biological and geological
  specimens.
• Over the 5-year voyage, he observed many
  phenomenon that influenced his thinking
• Marine fossils at high altitudes
• Earthquakes lifting large rocks huge distances
  very quickly
• Giant fossil versions of smaller living mammals

Glyptodon giant armadillo
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The Galapagos Islands

• Each island in the Galapagos supported animals
  and plants that were slightly different from each
  island and the mainland.
• It wasnt until Darwin took a closer look at his
  specimens back in England that he realized the
  finches he found were all different species from
  each other and the finch on the mainland of S.
  America.
• All the specimens were new to European
  scientists.
• The island species should not have resembled the
  mainland finch so closely UNLESS the finches had
  changed once they reached the islands.

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Artificial Selection

• Darwin hypothesized new species could appear
  gradually through small changes in ancestral
  species, but he could not see how this process
  worked.
• He turned to animal breeders.
• Artificial selection a way of breeding certain
  animals with desired traits that are exaggerated
  so the desired trait grows in frequency with each
  new batch of offspring.
• Eg. Dog breeds.
• This can also be called selective breeding.
• Darwin saw his idea working with animal breeders,
  so it was possible for it to work in the natural
  world given enough time.

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Think and Respond - Notes

• Explain how selective breeding works in the
  natural world.
• Think about
• Do animals chose mates they think might give
  their offspring better traits?
• If animals are selective, how do you think they
  might display their healthy, desirable traits?
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The Origin of Species

• With artificial selection in the back of his
  mind, Darwin cemented the four main ideas of his
  theory, natural selection
• Variation
• Heritability
• Overproduction
• Reproductive advantage
• By about 1840 Darwin most likely had his theory
  of natural selection formulated. He began
  writing a multi-volume book that contained all of
  his evidence for natural selection.
• It took him almost 20 years to gather all of his
  evidence, but in 1858 another scientist Alfred
  Russel Wallace proposed a theory that was almost
  identical to Darwins.
• They both presented at a symposium, and Darwin
  published his book, The Origin of Species, in
  1859.
• He didnt use the work evolution until the last
  page.
• EVOLUTION IS NOT THE SAME AS NATURAL SELECTION!

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Speciation

• Lets look at the dogs again. Are the Great Dane
  and the Chihuahua the same species?
• Explain why you do or dont think so.
• What does the word species mean?
• Speciation the formation of a new species.
• What kinds of factors will draw the line between
  different species?
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Natural Selection
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What is biodiversity?

• Biodiversity is the variety of life in an area
  that is determined by the number of different
  species in that area.
• It increases the stability of an ecosystem and
  contributes to the health of the biosphere.
• 3 Types of Biodiversity genetic diversity,
  species diversity, and ecosystem diversity.

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3 Types of Biodiversity

• 1. Genetic diversity variety of genes or
  inheritable characteristics that are present in a
  population.
• 2. Species diversity the number of different
  species and the relative abundance of each
  species in a biological community.
• 3. Ecosystem diversity the variety of
  ecosystems that are present in the biosphere.

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Theory of Natural Selection

• Darwin hypothesized that new species could appear
  gradually through small changes in ancestral
  species.
• Survival of the Fittest those best suited for
  the conditions survive while those less equipped
  die.

• Charles Darwin
• (1809-1882)

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4 Principles of Natural Selection Theory

• 1. Individuals in a population show differences
  or variations.
• 2. Variations can be inherited meaning passed
  down from parent to offspring.
• 3. Organisms have more offspring than can survive
  on available resources.
• 4. Variations that increase reproductive success
  will have a greater chance of being passed on
  than those that do not increase reproductive
  success.

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Key Example of Natural Selection

• The case of the Peppered Moth in Manchester,
  England is a well-documented study demonstrating
  the value of camouflage in Natural Selection and
  the continuing process of evolution. This case
  involves two variations of the same organism, a
  white-colored phenotype and a black-colored
  phenotype.

Prior to the industrial revolution, the dark phenotype was rare.

• Peppered Moths

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Environmental Pressure

• Prior to the industrial revolution, the white
  moths comprised 99 of the moth population. The
  white moths were protected by their ability to
  blend with the light-colored lichens, which lived
  on the bark of trees.
• During the later part of the 19th century (as the
  Industrial Revolution began), smoke particles
  produced by developing industry began to
  gradually darken the trunks of the trees on which
  the moths rested.
• In addition, the light-colored lichens covering
  the trees were killed by sulfur dioxide emissions
  from the new coal burning mills and factories.

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• Before

• After

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Impact of Natural Selection

• This change in the environment caused the white
  moths to become more visible and more likely to
  be eaten by birds, while the black form became
  better camouflaged. This situation led to a
  decrease in the population of white moths while
  the black moths were better able to breed and
  therefore increase in number.
• In 1848, the dark moths comprised 1 of the
  population and by 1959 they represented 90 of
  the population. So, in 100 years the frequency of
  dark moths increased by 1000 fold! 

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Think/Respond/Share

• Explain how evolution through natural selection
  can result in changes in biodiversity through the
  increase or decrease of genetic diversity within
  a population.

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Support for Evolution
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Comparative Anatomy

• Homologous structures
• anatomically similar structures inherited from a
  common ancestor.
• While homologous structures alone are not
  evidence of evolution, they are an example for
  which evolution is the best available explanation.

• Arm and Hand Structure

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Vestigial Structures

• Vestigial Structures structures that are
  reduced forms of functional structures in other
  organisms.
• Evolutionary theory predicts that features of
  ancestors that no longer have a function for that
  species will become smaller over time until they
  are lost.

• Pelvic Bone in Baleen Whale

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Analogous Structures

• Analogous Structures can be used for the same
  purpose and can be superficially similar in
  construction, but are not inherited from a common
  ancestor.
• Do NOT indicate close evolutionary relationships,
  but they do show that functionally similar
  features can evolve independently in similar
  environments.

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Comparative Embryology

• Embryo an early,
• pre-birth stage of an organisms development.
• Vertebrate embryos exhibit homologous structures
  during certain phases of development but become
  totally different structures in the adult form.

• Embryos

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Comparative Biochemistry

• Molecules in a species with a recent common
  ancestor should share certain ancient amino acid
  sequences.
• The more closely related the species are, the
  greater number of sequences will be shared.

• DNA

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Fossil Record

• Fossils provide a record of species that lived
  long ago.
• Shows ancient species share similarities with
  species that now live on Earth.
• Not all extinct fossils have a modern counterpart
  and some ancient species such as the horseshoe
  crab- have remained virtually unchanged for
  millions of years.

• Fossilized Bat

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Think and Respond

• Compare and contrast homologous structures and
  analogous structures.
• Give examples of a homologous structure and an
  analogous structure that are not mentioned in
  your notes.
• Are organisms able to consciously direct the
  course of their own evolution? Explain your
  answer.

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Fossilization Process
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Earths Early History

• No fossils exist from early Earth because of the
  caustic environment.
• The land
• Active volcanoes, constant meteor strikes,
  lightning storms.
• No solid ground for a few million years.
• The atmosphere
• Filled with poisonous gasses (carbon monoxide,
  methane, nitrogen gas).
• Water vapor and oxygen werent common for a few
  hundred million years.

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Rock Clues

• Fossil any preserved evidence of an organism.
  There are six types.
• Trace fossil any indirect evidence left behind
  (i.e. footprints, burrows, coprolite).
• Molds and casts molds are impressions, casts
  are molds filled with sediment.
• Replacement original material changed by
  mineral crystals that leave detailed replicas.
• Petrified and permineralized empty pore spaces
  are filled in by minerals (i.e. petrified wood).
• Amber preserved tree sap traps an organism and
  hardens.
• Original material mummification or freezing.

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Fossilization

• Fossils will not form in metamorphic or igneous
  rock only in sedimentary rock. Remains will not
  survive the heat or pressure necessary to make
  the other types of rocks.
• The organism dies and is covered with sediment.
• The sediment might replace the bones, the
  sediment might fill in holes, or the sediment
  might simply form a mold of the organism after it
  rots.
• Pressure from layers forming above help the
  formation of rock harden.
• Eventually the specimen could be exposed from
  erosion or a geological event.
• Paleontologists can read the record of fossils
  and rocks relative to each other, called relative
  dating. The lower a rock or fossil is, the older
  it is compared to something above it.

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Geologic Time Scale

• Geologic time scale a model that expresses the
  major geological and biological events in Earths
  history.
• Its divided into eras and periods. Each portion
  of the time scale is separated by a large scale
  event, like a mass extinction or an explosion of
  life.
• Precambrian
• 90 of Earths history.
• Earth formed, first life evolved.
• Paleozoic Era
• Cambrian explosion led to massive diversity in
  life forms over a short period of time.
• Fish, land plants, insects appeared and
  dominated.
• Reptiles were roaming the forests at the end of
  the Paleozoic Era.
• Mass extinction.
• Mesozoic Era
• Dinosaurs dominate, but the ancestors of birds
  and mammals roamed as well.
• A meteor hit the Earth near the end of Mesozoic,
  causing another mass extinction, forming what is
  called the K-T boundary.
• Cenozoic Era
• Current era where mammals are the dominant land
  animal.
• Humans have only existed on the planet for 10,000
  years. Thats only about 0.002 of the time the
  Earth has existed.

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Think and Respond

• What major event made it possible for the massive
  biodiversity to evolve so quickly during the
  Cambrian Explosion? Think about what basic
  material most organisms need to survive nowadays.
  
• If the entire history of the Earth was put into
  one day (24 hours), how long have humans existed?
  Give your answer in both minutes and seconds.

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