B2-Natural Selection

The Theory of Evolution

Animals and plants are better adapted to their environment and more likely to survive. This theory is called natural selection and was first put forward by Charles Darwin. 

Evolution is the slow, continual change of organisms over a very long period to become better adapted to their environment. These changes arise through mutations (changes in DNA).These adaptations are controlled by genes and can be passed on to future generations.

Examples of Natural Selection Today

- Peppered Moths

Peppered Moths can be pale or dark. Pale Peppered Moths are easily camouflaged amongst the lichens on silver birch tree bark. But in areas of high pollution, the bark is discoloured by soot. in these areas, the rarer, darker speckled varieties of the Peppered Moth are more common than the pale varieties. This is because the Pale Peppered Moths show up against the sooty bark where as darker ones don't so they are able to survive and breed in greater numbers. 

- Bactera and Penicillin

Some bacteria have become resistant to penicillin by natural selection, as follows:

1. Bacteria mutated. Some were resistant to the antibiotic penicillin;others were not. 

2.The non resistant bacteria were more likely to be killed by the penicillin. 

3. The penicillin resistant bacteria survived.

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