Transcript Evidence for Evolution

Topic
Evidence for evolution
Level
A Level
Outcomes
1. To describe the key points of Darwin’s theory of evolution by
natural selection
2. To state and explain the main pieces of evidence for evolution
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How did such tremendous diversity
of life come to exist on this planet?
Evolution
Each organism is unrelated
and is created independently
Life evolved many times
All life shares common
ancestry - all life is related
Life evolved once only
What Did Darwin Do?
Two key things:
1. He provided evidence for evolution
2. He proposed a theory to explain the
mechanism by which evolution occurs
Evolution
Darwin's definition: descent with
modification.
,
Darwin’s Evolution
1. Organisms have changed overtime
2. All organisms share common ancestors
3. Change is gradual
1. Fossil Record – Change over time
2. Shared Structures –
Common Ancestry
3. Similarities Between Embryos
– Change is gradual
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The Mechanism for Evolution
Natural Selection
Natural Selection
1. There is a "struggle" (metaphorically) to survive and
reproduce (organisms produce potentially more offspring
that can possibly survive)
2. Organisms show variation in characters that influence
their success in this struggle for existence.
3. Parents possessing certain traits that enable them to survive
and reproduce will contribute disproportionately to the
offspring that make up the next generation.
4. The population in the next generation will consist of a
higher proportion of individuals that possess whatever
adaptation enabled their parents to survive and reproduce.
5. Overtime the population will become adapted to the
environment
Requirements for Natural
Selection
• 1. Heritable variation for some trait
• 2. Differential survival and reproduction
associated with the possession of that trait.
Antibiotic resistance – an example
of modern day evolution by
natural selection
Variation in population  over production of offspring 
competition between offspring  best adapted survive and
reproduce  favourable characteristics passed onto next
generation
Why haven’t polar bears got white noses?
4. Genetic Changes
Darwin's Theory of Evolution by
Natural Selection
• Individual characteristics of an organism are
vitally important for its ability to survive and to
breed
• Individuals of a given species vary in many
characteristics
• Individuals produce more offspring than can
survive i.e. there is competition
• Only a small proportion of offspring will therefore
survive. If those characteristics which help the
oranThese individals that survive
Did humans evolve from
chimpanzees?
Evidence for Evolution
1.Fossil evidence shows the course of evolution
through time
2. Similar structures are shared by many
organisms
3. Comparative embryology (looking at
similarities between developing embryos of
different species)