Evolution

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Darwin
Made 4 main observations;
1. offspring are generally similar to their
parents
2. no 2 individuals are identical
3. organisms can produce large numbers of
offspring
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
generation
-Less well adapted individuals die before they
reproduce
-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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Better adapted individuals
survive and pass on their
characteristics
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

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

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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
others
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
glyptodonts?
6. Give the 3 important discoveries within
the study of fossils in times since
Darwin.
7. What is the problem with the fossil
record?
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

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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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HOW?!
What is this causing?…read more

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