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Theory of Natural Selection:. Darwin’s explanation for HOW evolution works. VOYAGE OF THE HMS BEAGLE : 1831 - 1836. Overpopulation (overproduction)- animals produce more offspring than survive. Variation - animals of the same species are different Change in environment-

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theory of natural selection

Theory of Natural Selection:

Darwin’s explanation for HOW evolution works.

7 steps to natural selection
Overpopulation(overproduction)- animals produce more offspring than survive.

Variation- animals of the same species are different

Change in environment-

a) Biological - food, predators, shelter, etc.

b) Physical…water, oxygen, temp, etc.

4. Struggle for existence- competition for water, food, & shelter

5. Survival of the fittest- the best adapted & strongest tend to survive longer & produce more offspring

6. Inheritance- favored/best fit/selected variations (characteristics) are passed on to offspring.

7. New species arise- “selected” individuals grow in number and become a new species that cannot reproduce with original species

7 Steps to Natural Selection

Darwin’s Observation: 13 or so species of finches on different Galapagos islands; these finches resembled the South American (mainland) finches more than say finches in Asia….


Jean Baptiste Lamarck: the outcaste!

  • used the fossil record as evidence
  • proposed a theory of evolution where organisms became better and better
  • Mechanism - ”use” and “disuse” leads to:
  • inheritance of acquired characteristics (you ‘acquire’ a phenotype in your lifetime and pass it on to your kids)
  • also means environmental influences can be inherited
hugo devries mutation theory
Hugo DeVries & Mutation Theory
  • New Characteristics suddenly appear
    • Mutation
  • These can be passed on and may or may not help a species become more fit
  • Helped to modify Darwin’s Theory
evidences for darwin s theory
Evidences for Darwin’s theory
  • Fossil record - horse lab
  • Homologous Structures
  • Vestigial structures
  • Artificial selection
Natural selection in action: the evolution of insecticide-resistance occurs in nature - individuals with the best fit genes that can resist the insecticide will survive….

Fig. 22.12



  • Similarities in characteristics resulting from common ancestry is known as homology.
  • 1) Homologous Structures: Same skeletal elements, but different functions

Human hand, cat limb, whale flipper, bat wing - they all have the same basic bone structure and design; So they have ALL evolved from a common ancestor with a similar ‘limb design’.




C) Vestigial organs, structures that are not used, but which had important functions in ancestors - still retained in descendents, so evolution/change has occurred.

Some Alleged Vestigial Organs in Man



Coccyx (tail bone)

Nictitating membrane of eye



Little toe

Wisdom teeth

Nipples on males


Nodes on ears "Darwin's points"

Ear muscles for wiggling

Pineal gland

Body hair


Artificial Selection: The selective breeding of domesticated plants and animals to encourage the occurrence of desirable traits.

  • Short period of time needed for Artificial Selection

Heredity: Characteristics that are passed down to offspring

Mutations: Changes that occur in the hereditary material

Mutant: The new form that survives a mutation and passes this trait on to offspring

Adaptation: A favorable variation within a species that may help an organism survive


Abiotic synthesis of organic monomers

  • Stanely Miller - simulated conditions on early Earth (no oxygen, reducing environment with inorganic gases like H2, CO2, NH3, CH4; lightning/UV with no ozone. Favored the synthesis of organic compounds from inorganicmaterial
  • The Miller-Urey experiments produced a variety of amino acids and other organic molecules (monomers).