Natural Selection (Edexcel A (SNAB) AS Biology)

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Natural Selection can lead to Adaptation & Evolution

  • Variation exists within a species population
    • Variation refers to the differences between individuals. It can be interspecific (between different species) or intraspecific variation (between individuals of the same species)
  • Some of this variation is due to random mutations, which introduce new alleles into a population
  • This means that some individuals within the population possess different phenotypes due to genetic variation in the alleles they possess
  • Environmental factors affect the chance of survival of an organism; they are said to act as a selection pressure
    • Predation, disease and competition are all examples of selection pressures, which make it difficult for all individuals in a population to survive
  • Selection pressures increase the chance of individuals with a specific phenotype surviving and reproducing over others
    • The advantageous alleles that code for the favourable phenotype will be passed on to offspring
  • When selection pressures act over several generations of a species, they have an effect on the frequency of alleles in a population through natural selection
    • Natural selection is the process by which individuals with a favourable phenotype are more likely to survive and pass on their alleles to their offspring so that the advantageous alleles increase in frequency over time and generations
  • Individuals that do not possess the advantageous alleles will most likely not survive long enough to reproduce, therefore reducing competition for resources
    • This will decrease the frequency of these non-advantageous alleles over time in a population
  • These changes in allele frequency will ultimately lead to evolution within the population

Evidence for evolution by natural selection

  • The theory of evolution by natural selection was first suggested by Charles Darwin
    • As evidence mounted in favour of this theory, it became increasingly accepted by scientists
    • In science, evidence provides confidence in theories until the point where enough evidence is gathered in order to accept the theory as an accepted scientific explanation
  • The peppered moth is an example of how natural selection leads to evolution over time 

Natural selection example 2The peppered moth is a well-known example of how natural selection leads to evolution

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Marlene

Author: Marlene

Expertise: Biology

Marlene graduated from Stellenbosch University, South Africa, in 2002 with a degree in Biodiversity and Ecology. After completing a PGCE (Postgraduate certificate in education) in 2003 she taught high school Biology for over 10 years at various schools across South Africa before returning to Stellenbosch University in 2014 to obtain an Honours degree in Biological Sciences. With over 16 years of teaching experience, of which the past 3 years were spent teaching IGCSE and A level Biology, Marlene is passionate about Biology and making it more approachable to her students.