Evolution
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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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Evolution

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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

  • 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

www.liverpoolmuseum.org/uk

Cryptic Frog

www.howstuffworks.com

Walking Stick

www.howstuffworks.com

Tartan Hawkfish

www.howstuffworks.com


“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)


Phylogenetic

Tree

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


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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