Adaptations and Evolution
What is a species?
A species is a group of organisms which can interbreed to produce fertile
offspring.
How do species change over time?
Members of a species can be slightly different or varied. This variation can be
passed on to offspring. The only way for new variation to occur is when an
organism’s genetic material is copied incorrectly. This is called a mutation.
Mutations are random events which change the genetic information of an
organism. This does not happen very often.
Mutations can affect single genes or whole chromosomes.
There are three types of mutation:
 Neutral mutations- have little effect on the organism
 Disadvantageous mutations- the mutation causes a change in the amino
acids produced and can cause health problems such as cystic fibrosis.
 Advantageous mutations- the mutation leads to a change in the
organism which gives it a better chance of survival, increased seed
production for example.
NOTE: Most mutations are harmful: advantageous mutations are very rare.
Although natural mutations are rare, certain factors can increase the risk of
mutation. These factors are called mutagenic agents. Some examples include
certain types of radiation or chemicals.
Adaptation:
If an organism possesses a characteristic which makes it well suited to its
environment, it is likely this characteristic was passed down from parent to
offspring. This inherited adaptation increases the organism’s chance of
survival.
Examples of adaptations:
Organism
Cactus
Habitat
Desert
Galapagos finches
Small isolated
islands
Adaptations
Reduced leaf
surface area and
thick waxy leaf
surface
Varied beak size
and shape
Advantage
Minimises
water loss
Adapted to
feed on food
sources
available
Evolution by Natural Selection
Evolution is the process by which a species changes over a long period of time. In 1858 Charles
Darwin and Alfred Wallace put forward the Theory of Evolution by Natural Selection.
Natural Selection is the survival of organisms which are best suited to their environment and is
described below:
1. Organisms produce more offspring than can survive in the environment.
2. These offspring are not all identical and show variation in their characteristics
3. This means that some organisms will be better suited (adapted) to the environment than
N ose - good
at finding food
Long legs - good
at running away
from predators
Coloured coat - good
camouflage to avoid
predators
others.
4. Those organisms that are best suited (adapted) to the environment will survive, breed and
pass on the characteristics that have made them well adapted to the environment.
5. Those organisms that are not as well suited to the environment will die before they can
breed and will therefore not pass on those characteristics that have made them not as well
adapted to the environment.
6. The process of natural selection is repeated over and over again and results in organisms that are
very well adapted to living in their environment.
Environmental factors that affect organism’s survival
Organisms can gain an advantage by being well adapted to certain environmental factors e.g.
1. Factor: Predation
Adaptation: Camouflaged coat, fast runner
2. Factor: Cold temperatures
Adaptation: Furry coat, layers of fat
3. Factor: Disease
Adaptation: Resistant to disease
4. Factor: Competition
Adaptation: Able to get food (good hunter/forager)
The Peppered Moth
The peppered moth exists in two forms:
1. light brown with dark speckles – light form
2. Black (melanic) – dark form
Both moths fly by night and rest on trees during the day.
Non polluted areas
light form is well camouflaged
Tree bark is covered
in lichens
dark form is not well camouflaged
because of this the dark form is more likely to be eaten be predators while the light form is more
likely to avoid predators and survive.
Polluted areas
light form is not well camouflaged
Lichens are killed by high
levels of sulphur dioxide
Tree bark is covered in
dark form is well camouflaged
soot
because of this the light form is more likely to be eaten be predators while the dark form is more
likely to avoid predators and survive.
Conclusion
A survey in the 1950’s showed that the light form was more common in non-industrial areas and
that the dark form was more common in industrial areas.
Pollution controls have resulted in the light form returning to areas that were previously polluted.
Speciation:
Speciation is the process by which one species evolves into two or more
separate species.
Isolation
Mutation
Natural
selection
Speciation
• Populations of a species become separated
• Because of this separation, the populations cannot
interbreed
• The populations in different areas will likely to undergo
different mutations
• The organisms in each population become more suited
to their own environments
• After a long period of separation, the two populations
are too genetically different to interbreed.
• they are now two distinct species.