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Evolution - PowerPoint PPT Presentation

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Evolution. The theory that organisms have changed gradually over time. Evidence to support the Theory of Evolution. Fossil Record - Law of Superposition Comparative Anatomy: Homologous Structures Analogous Body Structures Vestigial Body Structures Comparative Embryology

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The theory that organisms have changed gradually over time.

Evidence to support the Theory of Evolution

  • Fossil Record - Law of Superposition

  • Comparative Anatomy:

    • Homologous Structures

    • Analogous Body Structures

    • Vestigial Body Structures

  • Comparative Embryology

  • Comparative Biochemistry (genes/proteins)

  • Direct Observation

Fossil Record

  • Evidence of change over time

  • Relative age of extinct organisms

  • Age of the Earth

Law of Superposition: Older fossils in bottom layers; younger ones in upper layers

Sedimentary Rock Layers

Fossil Evidence:

  • Once living remains of organisms

  • Limited:

  • Type of material preserved (bone, shell, impressions, amber)

  • Incomplete record

  • Easily disrupted

Comparative Anatomy

  • Compares structures of different organisms living today

  • Homologous Structures – Parts on different organisms that are similar in structure (and sometimes function) and seem to indicate common origin – common ancestor.

  • Indicate divergent evolution – things becoming more different.

2. Analogous Structures – similar in function and appearance, but not in origin.

Illustrate convergent evolution – things becoming more similar.

Bird Wing

Fly wing

Analogous Structures

3. Vestigial Organs - traces of homologous structures; no apparent use.

Comparative Embryology

Comparative Embryology

  • shows early developmental stages in embryos of different vertebrate species is very similar

  • Inherited same basic body plan from a common ancestor

  • Become distinct at later stages

Genetic Evidence

  • Each new generation of organisms in a population shows some change or variation as a result of:

    • Mutations

    • Meiosis & fertilization

Comparative Biochemistry

Similar organic compounds (proteins, etc.)

Humans and chimp DNA – 98% similar

Humans and other mammals – 80% similar

Direct Observation

Rapid evolution

  • Antibiotic resistant bacteria

  • Resistance of insects to pesticides

  • HIV strains

How does evolution occur?Lamarckism vs. Darwinism

  • Jean Baptist Lamarck (1744 – 1829)

    • “Acquired Characteristics” develop and are passed on to offspring.

    • Experimentation failed to support Lamarckism

  • Charles Darwin (1809-1882)

Influences on Darwin

  • 1. Worked as naturalist on HMS Beagle for 5 year voyage

    • Collected fossils and specimens

    • Noted tremendous biodiversity

    • Galapagos organisms unique yet similar to species elsewhere

    • Formulated his idea of “Descent with Modification” (changes occur from one group of descendants to the next)

Descent with Modification

Voyage of the Beagle

2. Studied Charles Lyell – Geologist who said,

“The present is the key to the past.” The same forces acting on earth in the past are continuing today.

3. Studied work of Thomas Malthus - 1798

  • Human population growing faster than food supply - creates competition

  • Darwin extended idea to other organisms.

4. Observed that organisms produce more offspring than can survive

5. Observed the Struggle for Existence - Competition

6. Noted Artificial Selection

  • Farmers and breeders practice selective breeding to produce preferred offspring.

  • Darwin questioned

    • Is there a force in nature that simulates artificial selection???

Adaptations are physical or behavioral traits that make an organism better able to survive in its environment.

Sea Dragon


Cryptic Frog


Walking Stick


Tartan Hawkfish


“On the Origin of Species by Means of Natural Selection” published in 1859

  • Summary of Theory of Natural Selection:

    1. Overproduction of Offspring (more produced than can survive)

    2. Variation within a population

    3. Struggle to survive creating competition

    4. Successful reproduction - Individuals with better adaptations pass these on to offspring (survival of the fittest)



Darwin envisioned the tree of life

Sources of Variation

  • S– sexual reproduction

  • C – crossing over during meiosis

  • A – assortment of alleles during meiosis

  • M - mutations

Pepper Moths - England

  • Original color – 99% white (white bark on trees)

  • Industrial Revolution, 1850s – produced smog

  • Environment changes - 1890s - 99% black (dark bark on trees)

Each new offspring in a population draws its genes from the same gene pool.

Gene Pools

Which trait was a better adaptation and so selected for?

How did this affect the frequencies of the different alleles?

Population Genetics

  • Natural Selection acts on individuals, BUT

    populations evolve

  • An individual’s genotype remains constant

  • A population’s gene pool (entire collection of genes in a population) evolves as allelefrequencies change due to natural selection

History of Earth

  • Earth is @ 4.6 billion years old –

  • Early earth –

    • hostile environment – volcanoes, lightning, meteorites, UV light

    • Primitive atmosphere: CH4, NH3, H2, H2O,

  • All elements for life present – but no pure oxygen

Origin of Life

Primordial soup hypothesis: Primitive atmosphere filled with carbon, hydrogen, nitrogen, water vapor - bombarded by lightning and uv radiation, producing organic compounds and precursors to first cells, which ended up in oceans

  • Stanley Miller’s Experiment1953 – University of Chicago

  • After 1 week simple organic compounds including amino acids were present

Origins of Life: Oceans as Nursery

Simple compounds

Complex compounds

Primitive precells


Prokaryotes to Eukaryotes

  • First were heterotrophic prokaryotes which absorbed simple organic compounds.

  • Next, chemosynthetic prokaryotes

  • Next, photosynthetic autotrophs which produced oxygen

  • Led to development of eukaryotes and more complex organisms

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