The formation of new biological species is called speciation. Speciation is a result of:

  1. isolation
  2. mutation
  3. selection


The diagram illustrates what could happen to populations of animals, which become geographically isolated. Once two groups are isolated different mutations occur in each group. If the environments differ, different adaptations are favoured by natural selection.

This leads to different characteristics evolving in each group as time passes. Eventually the groups become so different that if they come together again they are unable to interbreed and are now separate species.

Allopatric speciation

Allopatric speciation is when new species arise due to isolation of a population by geographical barriers. Features such as rivers or mountain ranges isolate populations of animals and plants.

Movement of land-masses by continental drift led to geographical isolation millions of years ago.

Sympatric speciation

Sympatric speciation is when new species arise despite occupying the same geographical area.

  • Ecological barriers - although groups are not geographically isolated from each other they may be isolated by occupying different habitats or breeding areas, pH and salinity.
  • Behavioural barriers – a population may carry out complex mating rituals that may create a barrier to reproduction. Different timings, locations or mating dances may result in members of a population, who are not geographically separated, not being able to mate with each other.

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