Explaining Evolution 5 : What is mutation?


The 5th in our series of science blogs exploring evolution looks at mutation.

Explaining evolution 5 – What is a mutation

Fossils have a provided a substantial amount of evidence that allows scientists to chart the development of living organisms over billions of years. So how do species of plants and animals develop? Scientific observation has shown that living organisms usually produce offspring that are very similar to the parents but, very occasionally, there are observable or recordable differences between the parents and the offspring (e.g. the offspring is slightly taller, more prone to a disease, or a slightly different colour, etc). These changes are called mutations and could be negative – for example a male duck with slightly different colouring will be chased away from the flock by other male ducks and will not be allowed to breed. Mutations may be neutral – for example an increased or decreased sense of smell may not change the feeding success of a swallow that depends on speed and agility of flight to catch flying insects. Occasionally a mutation will be positive – for example slightly improved eyesight in a single blue tit may allow it to spot a sparrowhawk at a slightly further distance than others in its flock and so take evasive action earlier than its companions.

Negative mutations are unlikely to continue because the chances of surviving to breeding stage are reduced. However, neutral and positive mutations may become established in a population, especially when changing environments on Earth are considered.

It is important to appreciate that the Earth’s natural environments are constantly changing and have changed over billions of years. Seasons, weather patterns, earthquakes, volcanoes, atmospheric gases and dust, the amount of sunlight, warming/cooling, etc. affect all living organisms that might thrive or die in new environments. The changes in environment and populations of living organisms may present opportunities for mutated individuals. For example, there is well documented evidence that a mutation (darker colour) allowed the peppered moth to survive predation in soot-polluted Britain during the Industrial Revolution. The darker moth could not be seen on darkened, soot-polluted trees whereas the light-coloured peppered moth was seen by its predators.

The dark peppered moth is an example of a ‘bottle neck’ extreme situation whereby a mutation becomes the norm in a population. Another example could be the case of the blue tit given above. If there were an increased population of sparrowhawks then it is possible that the blue tit population would be so reduced that the ‘mutated’ blue tit with slightly improved eyesight might be one of a few survivors of the flock, leading to the mutation becoming more common – possibly the norm.

Recent DNA research and evidence has substantially supported the concepts of mutation, quantifying the science and using proven principles to develop species for improved yield and survival e.g. genetically-modified rice.

Now that there is a proven mechanism for species developing we can now try to answer the question, ‘How do species of plants and animals develop?’ (See the next blog: Explaining evolution  – Darwin’s theory of evolution.)

John Roach

Tutor

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