Natural Selection

Natural selection is a mechanism (a way) to explain how evolution can happen. The idea is credited to Charles Darwin.
Natural selection is the process in which the environment ‘selects’ favourable characteristics, reducing the frequency of unfavourable characteristics. This means that after many generations of selection, a species will become better adapted to its environment.
Evolution by natural selection occurs in the following steps:
  1. In a population (e.g. of animals such as finches) there are differences (variations) between individuals; not all members of one species are identical.
  2. Some members of the population don't reproduce, their characteristics are not passed on and are removed from the population.
  3. Other members that survive and reproduce are well suited to their environment because they have favourable characteristics. Scientists call this survival of the fittest.
  4. The favourable characteristics are passed on to the offspring (babies) and they become more and more common in the population


Natural_Selection_-_Darwins_finches.jpg
Darwin believed that natural selection was how different species eventually evolved. He visited the Galapagas Islands and saw lots of different finches. He thought they originally came from the same ancestor but through natural selection now look different.
An example of Natural Selection - The case of the English peppered Moth
The English peppered moth rests on tree trunks during the day. Its speckled grey colouring provides a good camouflage on the lichen-covered trunks. In about 1850, a black English peppered moth was discovered in Manchester. It was disadvantageous for these moths to be black as they stood out against the white lichen and were therefore easily seen by predators.
With the spread of the Industrial Revolution and the expanding use of steam power, pollution became a problem in large cities. The trees once covered in lichen turned black. The number of black moths increased dramatically and by 1895 they made up about 98% of the population of English peppered moths. How did the moths get to be black? Natural Selection!
Peppered_Moths.jpg
Two different variaties of the peppered moth. They are on a tree that is covered in lichen.

Peppered_Moth_Distribution.jpg
The distribution of peppered moths in the 1950's. The black variety is in industrial areas and the light variety is in rural farm areas with no pollution.

ACTIVITIES.
1. Modelling Natural Selection - group work (Add your results to the discussion page).
2. Read the information on this page and copy the notes into your book or OneNote.
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