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Darwin s Theory Evidence of Evolution The Fossil Record What is Evolution? -Evolution is the change in the hereditary features of a species over time. – PowerPoint PPT presentation

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Title: Darwin

Table of Contents
  • Darwins Theory
  • Evidence of Evolution
  • The Fossil Record

What is Evolution?
  • -Evolution is the change in the hereditary
    features of a species over time.
  • A species is a group of similar organisms that
    can mate with each other and produce fertile
    offspring. Today, we have identified more than
    1.7 million species.
  • How do species change over time?

Lamarcks Theory
  • -Jean Baptiste de Lamarck (1809)
  • Proposed the Theory of
  • Acquired Characteristics
  • which states that species
  • change over time by keeping
  • traits that their parents
  • developed during their lifetime.
  • This theory was rejected once
  • we understood genetics.

Darwins Theory
  • -Charles Darwin (1859)
  • Proposed the Theory of
  • Natural Selection.
  • This theory states that organisms with traits
    best suited to their environment are more likely
    to survive and therefore pass on these favorable

- Darwins Theory
  • Darwin was a naturalist on the
  • HMS Beagle.
  • In Dec. 1831, he began a 5 year
  • voyage to collect and study plants
  • and animals from all over the world.

  • One stop on the voyage was The Galapagos Islands
    (a group of 19 small islands off the coast of

  • Much of Darwins Theories were developed after
    studying the unique plants and animals of the
    Galapagos Islands.

  • Darwin spent over 20 years collecting his
    thoughts and writing a book.
  • He presented his book, On the Origin of Species
    by Means of Natural Selection, in 1859.

Four Basic Points of Natural Selection
- Darwins Theory
  • -Overproductionorganisms produce more offspring
    than can possibly survive.
  • -Variationmany differences are found among
    individuals of a species due to meiosis and
    genetic inheritance.

- Darwins Theory
  • -Competitionsome variations allow members of a
    population to survive and reproduce better than
  • -Selectionover time, offspring of individuals
    with helpful variations make up more and more of
    a population.

Variations and Adaptations
  • -A variation is any difference between
    individuals of the same species.
  • -An adaptation is any trait that helps an
    organism survive and reproduce.

Examples webbed feet on a duck gills on a
  • -If enough variations occur in a population over
    time, a new species could result.
  • -The movement of individuals into or out of a
    population helps to bring about more variations.

What Brings About Change?
  • A sudden change in the climate or environment can
    bring about evolutionary change by suddenly
    favoring one variation over another.
  • Example Peppered moths of England. Eventually,
    a new species could form if the environmental
    change is drastic enough.

- Evidence of Evolution
  • Geographic isolation can also bring about
    evolutionary change.
  • Example Kaibab and Aberts Squirrels.
  • These two kinds of squirrels have been isolated
    from one another for a long time. Eventually
    this isolation may result in two different

Evidence for Evolution
  • -Similarities in Early
  • Development
  • All vertebrate embryos
  • resemble each other early
  • in development.
  • These similarities show an
  • evolutionary relationship
  • among all vertebrates.

- Evidence of Evolution
  • -Homologous Structuressimilar structures that
    related species have inherited from a common
    ancestor. Example the bones in a dolphins
    flipper, a birds wing, and a dogs leg

  • -Vestigial structuresbody parts that are reduced
    in size and do not appear to have a function.
  • Examples human appendix, hip bones in whales
    and snakes.
  • Scientists believe these once functioned in an

  • -DNA and Protein Similarities
  • organisms that are close
  • relatives have similar
  • DNA.
  • Example The DNA of humans and chimps differs by
    less than 1.
  • This supports the idea that primates all evolved
    from a common ancestor.

  • -Development of chemical resistanceorganisms
    that have genes that make them resistant to a
    particular chemical will be the only ones to
    survive in the presence of that chemical to pass
    on their traits. Examples
  • Antibiotic resistant bacteria
  • Pesticide resistant insects

  • -Fossil Evidence
  • A fossil is the preserved remains of an
  • organism that lived in the past.
  • Fossils show that many organisms from
  • the past are very different than
  • organisms alive today.
  • Types of fossils

- The Fossil Record
  • Click the Video button to watch a movie about

Petrified Fossils
Stone Casts
Rock imprints or molds
Preserved remains in amber or ice
How Do Fossils Form?
- The Fossil Record
  • Most fossils form when organisms that die become
    buried in sediments.

Fossil Formation Activity
- The Fossil Record
  • Click the Active Art button to open a browser
    window and access Active Art about fossil

Dating Fossils
  • Two methods for dating fossils
  • Relative dating fossils are dated according to
    the layer of rock in which they are found. This
    is just an estimate.
  • Radioactive dating fossils are dated by
    measuring the amount of radioactive material
    present. This is more accurate.

Radioactive Decay
- The Fossil Record
  • The half life of potassium-40, a radioactive
    element, is 1.3 billion years. This means that
    half of the potassium-40 in a sample will break
    down into argon-40 every 1.3 billion years. The
    graph shows the breakdown of a 1-gram sample of
    potassium-40 into argon-40 over billions of years.

Radioactive Decay
- The Fossil Record
  • Reading Graphs
  • What does the red line represent? What does the
    blue line represent?
  • The red line represents the amount of
    potassium-40. The blue line represents the amount
    of argon-40.

Radioactive Decay
- The Fossil Record
  • Reading Graphs
  • At 2.6 billion years ago, how much of the sample
    consisted of potassium-40? How much of the sample
    consisted of argon-40?
  • Potassium-40100 argon-400

Radioactive Decay
- The Fossil Record
  • Reading Graphs
  • At what point in time do the two graph lines
  • About 1.3 billion years

Radioactive Decay
- The Fossil Record
  • Interpreting Data
  • At the point where the graph lines cross, how
    much of the sample consisted of potassium-40? How
    much consisted of argon-40? Explain why this is
    the case.
  • 50 of each the half-life of potassium-40 is 1.3
    billion years, which means that half will break
    down into argon-40 every 1.3 billion years.

Fossil Record and Geologic Time Scale
  • Geologic Time Scale a calendar of Earths
  • Using the fossil record (all the fossils
  • scientists have collected) and fossil
  • dating techniques, scientists have
  • developed the Geologic Time Scale.

Earths History as a Clock
- The Fossil Record
  • Fossils found in rock layers tell the history of
    life on Earth. The history of life can be
    compared to 12 hours on a clock.

Precambrian Time and the Paleozoic Era
- The Fossil Record

Mesozoic and Cenozoic Eras
- The Fossil Record

Combining Evidence
  • -DNA evidence is a newer source of evidence.
  • -In most cases, evidence from DNA and protein
    structure has confirmed conclusions based on
    fossils, embryos, and body structure.
  • -In some cases, scientists have had to change
    their hypothesis.
  • -Scientists can use the combined evidence of
    species relationships to draw
  • branching trees diagrams that show how different
    groups of organisms are related.

A Branching Tree
- Evidence of Evolution
  • This branching tree shows how scientists now
    think that raccoons, lesser pandas, giant pandas,
    and bears are related.

How Fast Does Evolution Occur? Two Theories
  • -Gradualismvery slow change from one species to
  • Involves intermediate species
  • Supported by some fossil records (like the
    horse) but not all.

  • -Punctuated Equilibrium more rapid evolution of
    a species brought about by the mutation of just a
    few genes.
  • Supported by some fossil records and bacteria
  • -Today, scientists think both probably occurred.

Extinction and Evolution
  • -Extinction is the dying out of a species.
  • Occurs naturally because the environment is
    always changing. Through natural selection,
    species which are unable to adapt to a changing
    world are removed.
  • Earths history shows at least 4 mass
    extinctions followed by rapid explosion of new

Humans role in extinction of species
  • -Human overpopulation and human activities are
    contributing to the rapid extinction of thousands
    of species.
  • This led to the passage of the Endangered
    Species Act of 1973. As a result, many captive
    breeding programs were established. They are
    expensive and for some species, they may be too

Relating Cause and Effect
- Darwins Theory
  • In a graphic organizer, identify factors that
    cause natural selection.

Overproduction More offspring are produced than
can survive.
Variations Members of the same species differ.
Competition Offspring compete for survival.
Natural Selection
Selection Some variations make individuals
better fit for survival.
Environmental Change Changes can affect an
individuals survival.
Genes Genes that help determine survival are
passed from parent to offspring.
Links on Charles Darwin
- Darwins Theory
  • Click the SciLinks button for links on Charles

End of SectionDarwins Theory
Identifying Supporting Evidence
- Evidence of Evolution
  • Evidence consists of facts that can be confirmed
    by testing or observation. As you read, identify
    the evidence that supports the theory of
    evolution. Write the evidence in a graphic
    organizer like the one below.

Fossils show that organisms that lived in the
past were very different from organisms alive
Patterns of early development show that some
different organisms look similar during their
early stages.
Similar bodystructures in different speciesshow
that the organisms shareda common ancestor.
Links on Evolution
- Evidence of Evolution
  • Click the SciLinks button for links on evolution.

End of SectionEvidence of Evolution
Building Vocabulary
- The Fossil Record
  • After you read the section, write a definition of
    each Key Term in your own words.

Key Terms
petrified fossil
Fossils that form by minerals replacing remains
are called petrified fossils.
The rocks that fossils are found near contain
radioactive elements, which are unstable elements
that decay, or break down, into different
The theory of punctuated equilibria accounts for
the gaps in the fossil record.
A hollow space in the sediment in the shape of an
organism or part of an organism is called a mold.
The half-life of a radioactive element is the
time it takes for half of the atoms in a sample
to decay.
A cast is a copy of the shape of the organism
that made a mold.
The millions of fossils that scientists have
collected are called the fossil record.
relative dating
Scientists use relative dating to determine which
of two fossils is older.
A species is extinct if no members of that
species are still alive.
radioactive dating
A technique called radioactive dating allows
scientists to determine the actual age of fossils.
Gradualism proposes that evolution occurs slowly
but steadily.
End of SectionThe Fossil Record
Graphic Organizer
Fossil Formation
An organism dies in water.
The organism is buried under sediment.
Over millions of years, the sediments harden and
become rock, and the hard parts of the organism
are replaced by minerals.
The fossil becomes exposed on the surface of a
End of SectionGraphic Organizer
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