Speciation (AQA GCSE Biology): Revision Note

Darwin & Wallace

• While Darwin is well known for his theory of evolution by natural selection, he was not the only scientist working on the idea during his lifetime

• In 1858 Darwin published work together with naturalist Alfred Russel Wallace

  • Wallace also proposed the theory of evolution by natural selection, independently of Darwin

  • It was Wallace's work that prompted Darwin to publish On the Origin of Species in 1859

• Darwin and Wallace's ideas had a huge impact on biology:

  • They introduced the idea that all living organisms share an ancestor

  • The idea that life-forms are static was replaced with the idea that species change over time

  • Understanding natural selection is essential for the study of other branches of biology, such as genetics and ecosystems

Speciation

• Wallace worked worldwide gathering evidence for evolutionary theory

• He is best known for his work on warning colouration in animals and his theory of speciation, which has developed over time into a well established theory

• Speciation is:

the 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 and natural selection:

  • Populations of the same species can become isolated from one another due to the formation of a physical barrier (e.g. a new river or mountain range) – this is known as geographic isolation

  • The environment will be different on either side of this physical barrier (e.g. different climates or different food available)

  • The environmental differences on either side will provide different selection pressures; there is genetic variation (caused by mutation) within each population; in each population the individuals better adapted to their own conditions are more likely to survive, reproduce and pass on their favourable alleles to their offspring, so over many generations different alleles become more common in the two isolated populations

  • Over many generations, individuals from the two populations will have become so distinct (genetically, behaviourally, physically) that they will no longer be able to interbreed and produce fertile offspring

  • The two populations are now separate species

Use this image