Biology - Natural Selection (AQA Syllabus A)

One subject looked at in GCSE Science is evolution. This is the second of two quizzes looking at that topic and it focusses in particular on the process of natural selection.

The usual story behind Darwin's theory of evolution gives the impression that he came up with it when he visited the Galapagos Islands during the voyage of the Beagle. But that is not the case. It was more than 50 years later when it was published. It is true that it was down to the birds that he observed on his trip but it was only many years later that he started to develop his ideas.

Whilst looking through his notes, he came to believe that the Galapagos Islands birds were all types of finch that had somehow 'transmuted' (that's just a long way of saying 'changed') from one form into another. The main difference between the birds was their beaks. He kept his ideas to himself for a long time because he had no idea how or why that could have happened.

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Darwin read a lot and at some point had read about biological competition. To you, that is simple but in the 19th Century it was a radical idea. But it still wasn't enough. It was only when he read an essay about population that he began to understand. This essay prompted Darwin to suggest that plants and animals produce more offspring than are needed for survival. There will be variation amongst the offspring and only the ones that are well suited to the environment will survive and breed, passing on the favourable characteristics. This is the process by which natural selection, one of the key mechanisms at work in evolution, occurs.

Darwin proposed that natural selection had worked on the Galapagos Islands finches. He realised that if all of the finches had the same beaks, they would be eating the same food. Islands the size of the Galapagos would not have enough food for the large number of birds he had seen. He suggested that variation in the original finch population included some that had different beaks. This meant that they could eat food that was different to the other finches and so they were successful, bred and passed on their characteristics. Any variations that could not compete became extinct.

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  1. Darwin's theory of evolution was based on what?
    Disuse of body structures and acquired characteristics are key points of Lamarck's theory of evolution, which is generally regarded as being incorrect now. Mutagenic agents increase the rate of variation but there was no knowledge of these at the time of Darwin so he could not have based his theory on this idea
  2. A variation in a plant creates a variety that has seed pods that 'explode' when touched by an animal. How could this lead to natural selection of this characteristic?
    This question is testing if you know two things - plants need space to grow and natural selection. Spreading the seeds out further will reduce competition for space to grow. Reduced competition would mean the plants are more successful and the 'exploding seed pod' characteristic is passed on
  3. The structural similarities between the flippers of whales and the arms of humans are used to show what?
    Comparing structural similarities is scientifically called comparative anatomy. The closer the similarity, the closer the link and the more recently they shared a common ancestor
  4. Darwin's ideas were not well recieved when he published them in 1859. Which of the following is a reason why?
    As well as religious reasons, there was insufficient scientific evidence at the time and a knowledge of genetics and inheritance did not come until about 50 years later
  5. The example of dark peppered moths living in or near to British industrial cities following the Industrial Revolution, whilst light ones live in the countryside, shows what?
    The dark moths are better camouflaged on trees made dirty by the Industrial Revolution, fewer are eaten by predators and so natural selecton here favours the dark version of the moth. The opposite applies to the countryside
  6. What might happen to an individual that is not well suited to its environment?
    A poorly adapted individual will be unable to compete successfully for the resources it needs. Over time, genes that make a plant or animal will be lost from the gene pool of that particular population, leaving only the best adapted plants or animals
  7. Why is there always variation in any population?
    The combination of the genes passed on from each parent is random which means every individual of a species will be different
  8. Darwin's theory of evolution by natural selection failed to explain which of the following options?
    This question tests if you realise that genetics was unknown at the time of Darwin. His theory could describe evolution but could not explain it in terms of genetics therefore the second option is the correct answer as it includes the word genetics. It also tests if you know that there is more variation in a population as time progresses unless you are dealing with a critically endangered species where fewer and fewer individuals are produced each year
  9. Fossils have been used to support Darwin's ideas. Fossils of which of the following animals are often used?
    The evolution of the horse from a creature the size of a dog to the animal we know today, is often used to support the theory because there are lots of fossils for each stage of the process
  10. Variation in a population of dark brown beetles in a public park creates a green version. In which of the following situations would a positive natural selection be most likely to occur?
    In three of the situations the beetles could be crushed by people sitting or standing on them but that's not what the question is about. They would be camouflaged better on the grass than the black ones so they would be less likely to be spotted by predators. Because of this they would have more offspring and pass on the green gene to the next generation

Author: Kev Woodward

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