Variation and Selection

• Variation is the differences that exist between individuals. Variation within a species (intraspecific variation) means that individuals in a population can show a wide range of different phenotypes. Variation can be caused by genetic and/or environmental factors
• What are the three types of natural selection?

  stabilising selection, directional selection, disruptive selection
• Stabilising selection is where individuals with alleles for characteristics towards the middle of the range are more likely to survive and reproduce. It occurs when the environment isn't changing, and it reduces the range of possible phenotypes
• Directional selection is where individuals with alleles for a single extreme phenotype are more likely to survive and reproduce. This could be in response to an environmental change
• Disruptive selection is where individuals with alleles for extreme phenotypes are more likely to survive and reproduce. It is the opposite of stabilising selection because characteristics towards the middle of the range are lost. It occurs when the environment favours more than one phenotype