Evolution By Natural Selection - National 5 Biology Revision - BBC

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Pages

1. Mutations
2. Evolution by natural selection
3. Example of natural selection in action
4. Speciation

Evolution by natural selection

Evolution can be defined as the change in the frequency of a phenotype in a population over many generations.

Variation

Although members of a species have many features in common they are not identical to each other. Variation occurs as a result of mutations that create new alleles of genes.

Mutations can be inherited if they occur in DNA that is passed on to the next generation. In populations that produce offspring by sexual reproduction, variation also occurs as a result of individuals receiving different combinations of alleles from their parents.

New alleles produced by mutations can result in plants and animals becoming better adapted to their environment. Variation within a population makes it possible for a population to evolve over time in response to changing environmental conditions.

Natural selection

Individuals produce more offspring than their environment can support, and some die because of factors such as predation, food shortage or disease. These factors are known as environmental selection pressures and they determine which individuals will do best at surviving and reproducing.

Some individuals are better adapted to their environment than others as a result of characteristics they have inherited from their parents. The genes that produce these characteristics give them a selective advantage. They may have a better ability to avoid predators, compete for food, or resist disease.

These individuals are therefore better able to survive and reproduce than less well-adapted individuals. They pass on the versions of genes that produce their adaptations and the frequency of these alleles will increase within the population. Predation, competition and disease are examples of selection pressures.

Next pageExample of natural selection in actionPrevious pageMutations

More guides on this topic

• Revise: Ecosystems
• Revise: Distribution of organisms
• Revise: Photosynthesis
• Revise: Energy in ecosystems
• Revise: Food production
• Revise: Apparatus and techniques
• Video playlist

Related links

• BBC Science
• BBC Lab UK
• BBC Nature
• BBC News: Science
• SQA National 5 Biology
• The Guardian: Biology
• StudyJams
• Nature Detectives