• Question: How might the population of alleles become isolated and why does this isolation lead to the evolution of new species

    Asked by to Sarah, Izzy, Clem, Amelia on 18 Mar 2014. This question was also asked by .
    • Photo: Isabel Webb

      Isabel Webb answered on 18 Mar 2014:

      Populations of plants (or animals) could become geographically isolated from a population of the same species. This could happen naturally, such as due to seeds being carried over land by mammals, or seeds being carried over seeds by birds. Humans could also play a part in this , such as transporting organisms overseas on boats or planes. Once these populations are moved they will have different ‘selection pressures”, the different features in their environment that they need to adapt to.

      In these new environment, plants start adapting – for instance improve their root growth in dry soil or maybe their water use. Adaptation like this can occur due to mutations in their DNA (and so alleles) – and if the mutations are beneficial , they will stay. Eventually the mutations will make the new population so different from the old population that the two can no longer reproduce together – it is at this point that a new species has formed.

      Charles Darwin saw many examples of this in the birds called finches that he found on the Galápagos Islands – they had different sized beaks depending on what they had to eat on the different islands. You can see some of his samples, plant and animal at the Natural History Museum, if you ever get a chance to go there.

    • Photo: Amelia Frizell-Armitage

      Amelia Frizell-Armitage answered on 18 Mar 2014:

      Good question.

      Populations can become isolated in a number of ways. In the long term, when mountain ranges form, sea level rises and makes islands out of big land masses, or continents move apart, a population can be split in two. In the shorter term a flood, or a group of migrating birds flying the wrong way, or some rats getting trapped on a ship and transported across the ocean could break up a population.

      Once a population has been split into two groups like this, individuals do not meet to breed between groups, they can only breed with others in the same group. If the environmental conditions are different in the new location, the isolated population will start to adapt to those conditions. Over time the evolve to be better in that area. At first these adaptations might just be changing behaviour, but over time the actual genetics will start to change. The population will evolve new genes that are better adapted to that new environment.

      If the genes of the isolated population become very different to those of the old population, they will no longer be able to breed together even if they do meet again. Two individuals that cannot breed to produce fertile offspring are different species.

    • Photo: Sarah Harvey

      Sarah Harvey answered on 18 Mar 2014:

      Impressive question there!

      One thing I’d like to add is that populations can also be temporally separated. This is I guess easier to imagine happening in animals – but if for some reason some animals are nocturnal or have a different breeding season even though they inhabit the same area don’t come into contact with others then there won’t be any breeding between the two populations.

      I guess this could happen with flowering time in plants – then two populations could separate and eventually become separate species.

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