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Preview of Evolution

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Made 4 main observations;
1. offspring are generally similar to their
2. no 2 individuals are identical
3. organisms can produce large numbers of
4. populations tend to remain stable in size
- When too many young are produced ­
competition for food and resources
- Some are better adapted than others
- These survive long enough to reproduce
-Pass their characteristics on to the next
-Less well adapted individuals die before they
-Over a long time variations may arise- if
beneficial, help the organism to survive
-Over time lots of variations can occur and one
species can give rise to another
-This happens if the changes mean that the new
organisms are no longer able to interbreed with
each other
Darwin's conclusions...
1. There is a struggle to survive

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Page 2

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Better adapted individuals
survive and pass on their
3. Over time a number of changes
may give rise to a new species
Natural selection.
Process in which an environmental
factor determines which individuals
will survive
They are `selected'
Undergo a `selection pressure'
If it is not `selected'- it will be
outcompeted and die
Factors in the environment that
may act as selective forces...
Selective forces:
1.…read more

Page 3

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Predators- individuals may be
better adapted not to be seen,
or escape
3. Diseases ­ some may be
4. Physical and chemical factors-
if an organism can survive in
e.g a desert, or somewhere v.…read more

Page 4

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OR reproductive barriers e.g.
biochemical change ­ prevents
fertilisation, physical change ­ sex
organs may no longer be compatible or
behavioural change- courtship dance
might not be recognised)
So some individuals can't reproduce with
So variations will only spread down part
of the group
Eventually become very different
= 2 new species
Evidence for evolution.
Using pages 216 and 217, answer the
following questions.
1. What facts have fossils from the past
shown us?
2.…read more

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What could the fossils of brachiopods
be used for?
5. What is interesting about the
relationship between armadillos and
6. Give the 3 important discoveries within
the study of fossils in times since
7. What is the problem with the fossil
8. Describe the 3 types of modern
evidence that help us to prove the
theory of evolution.
Evolution today.
How it works...
1. Variation has to happen for
evolution to take place
2.…read more

Page 6

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Next generation are better
adapted for survival
Remember- genetic variation is
what makes a difference-
environmental variations can't be
passed on!!
If a new species evolves- diversity
is increased
Having a lot of populations that
are genetically different but can
still interbreed also increases
diversity e.g. humans
Evolution always occurring, due to
selection pressures.
e.g.…read more

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What is this causing?…read more


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