AQA GCSE Biology

Revision Notes

6.3.2 Speciation

Darwin & Wallace

  • Alfred Russel Wallace was a scientist who, after conducting his own travels around the world and gathering much evidence, independently developed his own theory of evolution based on the process of natural selection
  • He published scientific papers on this theory with Darwin in 1858 (Darwin published his book, On the Origin of Species, the following year
  • Wallace is best known for:
    • His work studying the warning colouration of species (particularly butterflies) and how this must be an example of a beneficial characteristic that had evolved by natural selection, as the warning colouration helps to deter predators
    • Developing the theory of speciation


  • Alfred Wallace did much pioneering work on speciation but more evidence over time has led to our current understanding of the theory of speciation
  • Speciation is a process that results in the formation of a new species
  • When populations of the same species become so different that they are unable to interbreed and produce fertile offspring, they are considered different species and speciation has occurred
  • Speciation can occur as a result of a combination of isolation (when populations of the same species become separated) and natural selection:
    • Populations of the same species can become isolated from one another due to the formation of a physical barrier (eg. a new river or mountain range) – this is known as geographic isolation
    • The environment will be different on either side of this physical barrier (eg. different climates or different food available)
    • The environmental differences on either side will provide different selection pressures and natural selection will cause a different set of characteristics to become more common in the two isolated populations
    • Over many generations, individuals from the two populations will have become so distinct (genetically, behaviorally, physically) that they will no longer be able to interbreed and produce fertile offspring
    • The two populations are now separate species

Speciation, downloadable IGCSE & GCSE Biology revision notes

The process of speciation

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