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Life on Earth Revision. Variation of Life on Earth. All living things, both those alive and those that are now extinct all originate from the simple living things that first appeared 3500 million years ago. Evidence for evolution comes from: Fossils DNA testing. Natural Selection.

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Variation of Life on Earth

  • All living things, both those alive and those that are now extinct all originate from the simple living things that first appeared 3500 million years ago.

  • Evidence for evolution comes from:

    • Fossils

    • DNA testing

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Natural Selection

  • Natural selection involves:



Increased chance of survival


Increases numbers in population

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Selective Breeding

  • Selective Breeding involves:

Selecting individuals with desired features

Breeding them

Selecting offspring with desired features

Breeding them

Increasing numbers with desired features

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Multi-cellular Organsism

  • Evolution of multi-cellular organisms has lead to;

    • The development of receptor and effector cells.

    • These are linked by neurones.

    • The neurones link via the CNS

      (See Brain and Mind)

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Theories of Evolution

  • Lamark – suggested organisms developed through an inner urge to improve.

  • Cuvier – suggested the fossils in layers of rock were due to God wiping old species out with catastrophes , e.g. Noah’s Ark.

  • Darwin – suggested evolution occurred by a process of natural selection or survival of the fittest.

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Darwin’s Theory

  • Was rejected at first for religious reasons as the Bible was taken literally at the time.

  • Was eventually accepted because it explained how evolution occurred.

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Data and Theories

  • Understand the difference between data and theories.

  • Appreciate that data could be explained by a number of theories.

  • Appreciate that theories require original thought.

  • Understand why theories are accepted or rejected.

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Key Terms with Theories

  • Understand the terms

    • Corroborate; make more certain

    • Confirm; strengthen, verify.

    • Falsify; forge, misrepresent.

    • Prove; to establish as truth

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Causes of Variation

  • Random changes in the DNA called mutations occur.

  • If in sex cells these are passed on to the offspring.

  • Sometimes these changes gives increased chances of survival.

  • The frequency of the mutation then starts to increase.

  • This can eventually lead to new species.

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  • Random Mutation.

  • Random Breeding.

  • Natural Selection.

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Human Evolution

  • Humans species have evolved from a common ancestor.

  • All other hominids have become extinct.

  • The evolution of intelligence is very important to the evolution of humans.

  • The ability to learn from experience has given humans a selection advantage.

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Under Pressure

  • Organisms are dependent on the environment and other species.

  • Organisms compete.

  • Large changes in the environment can result in extinction of a species.

  • Extinction of one species can then affect other species in the food web.

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Under Pressure (cont.)

  • Changes that can affect an organism include;

  • Major change in conditions

  • A new species that is a competitor, predator or disease.

  • Another organism in the food web becomes extinct.

  • Many species have become extinct, sometimes mass extinctions occur e.g. dinosaurs.

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  • There is evidence of an increasing rate of extinctions.

  • Retaining biodiversity may be important for food and medicines.

  • A species has less chance of becoming extinct in an ecosystem that is diverse.

  • Maintaining diversity is an important part of using the environment in a sustainable way.

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Origins of Life

  • The first living things developed from molecules that could copy themselves (DNA).

  • These molecules were produced by the unique conditions at the time.

  • If conditions had been different, natural selection could have produced different results.

  • Although there is no proof of life elsewhere, there are so many galaxies, stars and planets that some scientists think life elsewhere in the Universe is likely.