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Evolution by natural selection
Introduction
• Natural selection happens when individuals
of a population have differing
characteristics caused by their genes
(heritable)
• Differences between individuals mean that
some individuals are better adapted to their
environment than others
Why do individuals of the same
species have variations in their
characteristics?
•Because of differences in their genes.
•Genes are made up of DNA and are found in
every cell of your body
•The genetic code is a set of instructions for
making an entire organism with each gene
coding for a specific protein.
Where does variation in the genes
come from?
• When cells divide or gametes are formed the DNA
is replicated (copied)
• Sometimes errors occur in the copying called
mutations. Mutations are random
• These mutations change the code for making an
organism.
• Most of the time this has no effect or a negative
effect on the organisms survival chances
• But sometimes these mutations can be beneficial
What will happen to the survival
chances of better adapted
individuals?
More likely to survive and have more
offspring than less well adapted
individuals.
What effect does this have on the gene
pool?
•When organisms reproduce they pass on their genes
•Organisms with beneficial characteristics are more
likely to pass on their genes
•The frequency of the genes that cause these beneficial
characteristics will increase from generation to
generation
Darwin’s finches
These finches are found on different islands of the Galapagos
How are they
similar?
How are they
different?
Why?
Darwin’s finches
There are at least 13 different species of finch found in the
Galapagos
Similar because they
share a common
ancestor
Different because of
differing selection
pressures on different
islands
Example of natural selection leading to speciation. Can no longer
interbreed
Is evolution just a theory? What evidence
is there to support it?
•Fossil record provides
evidence for evolution
•Incomplete needs certain
conditions to delay decay e.g.
low temperature, low oxygen,
highly acidic soil
•Often only hard parts e.g.
skeleton are well preserved
Artificial selection
Is evolution still happening?
Can you think of any examples?
•Antibiotic resistant bacteria
•Insecticide resistance
Are acquired characteristics heritable?
How do we know?
Why is evolution such a
controversial topic?