Download 7.3 Natural selection - science

GCSE
Key words: characteristics, ‘fittest’
Biology 1b Evolution and Environment
CORE
How the giraffe got its neck
How does Darwin’s theory explain a giraffe’s long neck?
Due to natural variation, the ancestors of modern
giraffes would have had necks of different length.
Giraffes with longer necks would have been able
Explain how Darwin would have
to reach more food than those with shorter necks.
explained the giraffe’s neck
As a result, the long-necked giraffes were
more likely to be healthy and live to produce
more high-quality offspring.
This, in turn, would increase the chances of
their long-necked characteristic (an adaptive
trait) being passed on to future generations.
GCSE
Biology 1b Evolution and Environment
CORE
Objective
What is natural selection?
Success Criteria
By the end of the lesson I:
• can explain that organisms in a species all vary from each
other
• can explain that some organisms are more likely to survive
and breed as they have ‘better’ chanracteristics.
GCSE
Biology 1b Evolution and Environment
CORE
Natural selection
GCSE
Biology 1b Evolution and Environment
CORE
What do you think
‘Natural Selection’
is defined as?
Natural selection occurs when
successful characteristics,
produced by chance (random)
mutations, enable organisms to
survive and breed.
GCSE
Biology 1b Evolution and Environment
CORE
ANOTHER EXAMPLE
The peppered moth
• The peppered moth is a common insect in Britain with
two forms: the dark form and the light form.
• The light form has small black specks just like it
has been dusted with pepper. This is variation.
300 years ago most peppered
moths were the light form.
After the industrial revolution
the dark form became
commonest in city areas.
GCSE
Biology 1b Evolution and Environment
CORE
Natural selection of dark form in industrial areas
Tree surfaces are dark because of air pollution
Pale lichens are killed by sulfur dioxide
Dark moth less likely to be seen and eaten by bird predators
Dark moths more likely to survive to breed
Repeated over generations
GCSE
Biology 1b Evolution and Environment
CORE
Natural selection of light form in clean areas
Tree surfaces are pale.
Pale lichens grow on the tree bark.
Light moth less likely to be seen and eaten by bird predators
Light moths more likely to survive to breed
Repeated over generations
GCSE
Biology 1b Evolution and Environment
CORE
EXAM TIP
Weaker members of the species may die from
1. Disease
2. Lack of food (or being caught by predators)
3. Variation in the climate (a very wet/cold/hot period of
weather)
The survival of organisms with the ‘best’ characteristics is
known as ‘survival of the fittest’.
The ‘best’ characteristics can be
•
Fastest
•
Ability to find food
•
Fight off disease
•
Survive a short change in weather well
GCSE
Biology 1b Evolution and Environment
CORE
EXAM TIP
Draw a flowchart to explain the natural selection of oysters
from Malpeque Bay (1915-1940) p113 in text.
A disease killed most of the Oysters in Malpeque Bay, Canada
Fortunately a few of the shellfish carried a mutation
which made them resistant to the disease.
These were the only ones to survive and breed.
Repeated over generations.
GCSE
Biology 1b Evolution and Environment
CORE
What happens when habitats change?
Adaptive evolution ensures that individuals within a species
have traits allowing them to survive and reproduce in their
habitat.
If the habitat changes, however, successful traits can
become a disadvantage.
For example, if global warming caused
Arctic snow to melt, brown rabbits may
be better camouflaged and so more
likely to survive than white rabbits.
Individuals that fail to reproduce, compete effectively for food
or survive against new predators will eventually die out. If the
last individual of a species dies, the species is extinct.
GCSE
Biology 1b Evolution and Environment
CORE
GCSE
Biology 1b Evolution and Environment
CORE
Objective
What is natural selection?
Success Criteria
By the end of the lesson I:
• can explain that organisms in a species all vary from each
other
• can explain that some organisms are more likely to survive
and breed as they have ‘better’ chanracteristics.
GCSE
Biology 1b Evolution and Environment
CORE