natural selection

• variation: differences between individuals. it can be interspecific (between different species) or intraspecific variation (between individuals of the same species)
• variation exists within a species population

  some of this variation is due to random mutations which introduce new alleles into a population
• random mutations 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: 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 overtime in a population
• these changes in allele frequency will ultimately lead to evolution within the population
• the theory of evolution by natural selection was first suggested by charles darwin
• as evidence mounted in favour of charles darwins natural selection theory, it became increasingly accepted by scientists
• 1. random mutation
  2. mutation becomes an advantageous allele for the environment
  3. individuals with this mutation are more likely to survive and reproduce, passing on advantageous allele to offspring
  4. individuals without mutation more likely to not survive and reproduce
  5. over time there is a gradual increase in proportion to individuals with advantageous allele compared to the ones without