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3 Introduction to natural selection

Evolution is central to biology and natural selection is the mechanism that produces adaptation.

  • In a single sentence, write down what you understand by the term 'adaptation'.

  • An adaptation is a morphological, physiological, biochemical, developmental or behavioural trait that gives an organism a greater ability to survive and reproduce in a particular environment.

For selection to occur there must be variation within a population, because if every individual is identical, there is nothing for selection to act upon. So, for example, there is variation in beak size in finches and those individuals with beaks well-suited to a particular size of seed do better than others in the population and therefore are selected for.

  • Write down a few sentences that illustrate your understanding of natural selection.

  • Natural selection refers to the differential survival and/or reproduction of organisms due to their physical attributes or phenotype. The concept of selection is central to the theory of evolution by means of natural selection, formulated by Charles Darwin, which forms the cornerstone of many explanations of animal behaviour.

  • What three criteria must be met within a population of interacting individuals in order for natural selection to occur?

  • The three criteria are:

    • there must be phenotypic variation
    • phenotypic variation must be genetically determined (so that it can be inherited)
    • phenotypic variation produces variation in some component of fitness, such as survival or mating success, and is ultimately expressed as differential reproductive success.

There are three kinds of natural selection that will be considered in this course. How the frequencies of phenotypes within a population change in response to these forms of natural selection is shown in the accompanying figures.