Speciation (AQA GCSE Biology)

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

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

The process of speciation