Natural Selection (SQA National 5 Biology): Revision Note

The process of natural selection

• New alleles produced by mutation can result in plants and animals becoming better adapted to their environment

  • An adaptation is an inherited characteristic that makes an organism well-suited to survival in its environment or niche

• Natural selection is the process by which species change and adapt over time

• The process of natural selection occurs as follows:

  1. more offspring are produced than the environment can sustain

  2. variation exists among the resulting population

     • Some individuals inherit advantageous alleles and some may inherit disadvantageous alleles

  3. selection pressures act on the individuals in a population

  4. the best-adapted individuals are more likely to survive and reproduce

     • This is known as survival of the fittest

  5. advantageous alleles are more likely to be passed on to offspring

  6. these alleles increase in frequency within a population

Example: natural selection in rabbits

• The process of natural selection can be applied to fur colour in rabbits as follows:

  1. rabbits produce many offspring

  2. variation in fur colour exists within the resulting rabbit population

     • One allele codes for brown fur and another for white fur

  3. rabbits have natural predators, such as foxes, which act as a selection pressure

  4. brown rabbits are more likely to survive and reproduce due to having more effective camouflage

     • The brown rabbits can be said to have higher fitness than the white rabbits

  5. when the brown rabbits reproduce they pass on the allele for brown fur to their offspring

  6. the frequency of the brown fur allele increases in the population