Transcript Peppered Moth Powerpoint - Year 10 Life Science

Natural Selection
Year 10 Science Life
Natural Selection
In 1858, Charles Darwin proposed a process by which species change over
many generations.
 He had no knowledge of genetics because it had not been discovered at
the time
Darwin’s view of life : descendants of ancestral forms adapted to different
environments over a long period of time.
 The mechanism for adaptation is called ‘natural selection’, and is based on
a number of principles:
 Variation
 Competition/Survival of the fittest phenotype
 Favourable alleles increase
 Ability to reproduce increases
Darwin
Natural Selection cont…
Natural selection is the process where an environmental factor acts on
a population and results in some organisms having more offspring than
others.
 The factor that acts on the organism is called the selective agent.
The selective agent may be a predator, disease, natural disaster or
physical factor such as temperature.
 The individual that are favoured by the selective agent survive and
pass on their features to the next generation.
 The outcome of natural selection being that the species becomes
better adapted to their environment and survives longer.
Evolutionary Process by Darwin
Variation: Individuals vary from one another in many characteristics (even
siblings differ). Some variations are better suited then others to the conditions
of the time.
Competition: There is competition among the offspring for resources (food,
habitat etc.).
Survival of the fittest phenotype: The individuals with the most favorable
combinations of characteristics will be most likely to survive and pass their
genes on to the next generation.
Favorable combinations increase: Each new generation will contain more
offspring from individuals with favorable characters than those with
unfavorable ones.
https://www.youtube.com/watch?v=s
VVldxxbWig
Example of natural selection:
“The Peppered Moth”
The peppered moth existed in two forms white with black spots and all black.
 In city areas almost all peppered moths were black
 In country (rural) area all peppered moths were white
 The selective agents were birds (predation)
 The findings:
 In the city areas the trees were blackened by pollution any white moths resting on
the trees would be spotted and eaten, therefore the black moths survived longer.
The black moths produced black offspring, therefore the city population became
mainly black. The black peppered moth adapted to the city environment.
 In country (rural) areas, the air was cleaner and the trees were lighter. This made
the white peppered moths harder to see , the black moths were all eaten and so the
population became nearly all white as only white moths were breeding in these
areas. Now the white moths were better adapted to these areas.
Peppered Moth
Which picture is from which area?
- City?
- Country?
Peppered Moth
In England in 1850 the dark form of the moth
was virtually unknown. The map below
shows the distribution of the moth in
England in 1950.
1. What basic change occurred to the habitat
of the moth during the years following 1850?
2. How did this change affect the light form
of the moth?
3. Explain why (using the steps of natural
selection) the number of dark moths
increased dramatically from 1850 to 1950.
Use this to help you describe the steps of Natural
Selection with ‘Peppered Moths’ during the industrial
revolution. List each step and refer to example.
Sequence of events in natural selection
 1) Variation exists in a population (often due to mutation)
 2) A selection pressure occurs (specify what it is)
 3) Those with a favourable phenotype (specify what it is) will
be selected for, unfavourable phenotypes (specify what it is)
are selected against.
 4) Those with the favourable phenotype are more likely to
survive long enough to reproduce and passing on these
favourable genes to their offspring , so the next generation
will be genetically more like them and better adapted to the
environment. (what was the favourable phenotype)