3. Natural Selection
• The idea of natural selection was first
suggested by Charles Darwin over 150
years ago.
• Certain individuals gain an advantage over
other individuals they are in competition
with.
• This animal is therefore more likely to
survive and breed – natural selection.
4. Natural Selection
There is There is There is This results in:
variation in differential hereditary: The advantageous
traits: reproduction: trait allows the
Not all beetles
The brown
For example beetles have beetle to survive
reproduce to their and have more
some beetles full potential. Green brown offspring offspring. Over time,
are green and beetles are eaten because the trait if this continues the
some brown. so is mainly brown has a genetic whole population
beetles that basis. will be brown.
reproduce.
5.
6. Survival of the Fittest
• Reproduction is a very wasteful process.
• Animals and plants always produce way
more offspring than the environment can
support.
Fruit flies produce 200 offspring
• Why? every 2 weeks!
7. Survival of the Fittest
• Individual species show lots of variation
because of the different genes they inherit
• Only the offspring with the genes best
suited to their habitat will stay alive and
breed successfully.
• Many animals produce lots and lots of
offspring to ensure that at least some will
survive and pass on their genes.
8. What about mutation?
• New forms of genes result from changes
in existing genes.
• These changes are mutations.
• Mutations happen due to mistakes made
when copying DNA when cells divide.
• They introduce more variety into the genes
of a species.
Why is this important for evolution?
9. What about mutation?
• If the mutation that occurs results in a
characteristic that helps the animal
compete and survive then it will be passed
on to the next generation.
• Over time this mutation may become a
common gene in the population.
10.
11.
12. What do these animals have in
common?
They are all
extinct!
13. Extinction
• Extinction is the permanent loss of all the
members of a species from the face of the
Earth
In pairs:
• What might cause an animal to become
extinct?
14. Extinction
• Environmental changes (Dinosaurs)
– E.g. If animals suited to hot weather enter an ice age
• More competition (Birds species on Guam)
– If a mutation happens in one species that helps it
survive really well or a new species moves into the
area
• A new disease (Tasmanian devil)
– E.g. If a population of animals gets a disease which
none of them are resistant to. This is especially bad if
the whole population live close together (e.g. on an
island)
15. Questions
• What is the link between natural selection
and mutation?
• Explain how good eye sight in rabbits has
come about in terms of natural selection.
• Name three causes of extinction.
• Explain why the dinosaur became extinct.
