AQA Human Biology - Human Impact on Evolution (Unit 5)


Human Impact on Evolution

These notes cover Unit 5, Topic 8 which includes the following topics:  'Alleles and Variation', 'Selection', 'Isolation and the Formation of New Species' and 'Human Activities and Selections'

Alleles & Variation

  • Mutation = change to the quantity or structure of an organism's DNA.            
  • Alleles = different forms of the same gene caused by a mutation changing the sequence of bases in that gene. 

If the mutation is in a gamete, the mutation will be passed onto offspring. This may change the phenotype (characteristics resulting from alleles) of the offspring. 

  • Phenotypic variation = total variation observed in one character, from both genetic and environmental factors.
    • Genetic factors (Genotypic variation): Selective advantage, crossing over/random assortment during meiosis and random fertilisation.
    • Environmental factors: Selection pressures, competition for food/mates, disease.

In certain environments, an individual who inherits a mutation may be put at a selective advantage making them more likely to survive and reproduce, producing offspring with the mutant allele. This increases the frequency of that allele within the population --> evolution.

ExampleResearch suggests 80% headlice in Wales are resistant to chemicals commonly used against them. This would have been caused by a mutated allele which provided resistance, and would have given those with it a selective advantage.


  • Intraspecific competition = competition between organisms of the same species. This occurs when there are more organisms than the environment can support.
  • Selection pressure = environmental force altering the allele frequency in a population.

Offspring best suited to environment survive, reproduce and pass on successful alleles (natural selection). These survivors have the selective advantage. They may be better at finding a mate, better at running from predators or less susceptible to disease. Those that fail to adapt don't survive and don't pass on their genes.

One example of this is resistance to antibodies in bacterial populations:

  • Bacteria reproduce very quickly, changes in allele frequency can be observed over relatively short time scale.
  • Bacteria carry plasmids with genes for antibiotic resistance. They vary in susceptibility for each antibiotic.
  • When antibiotics are taken, the…


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