Variation with a Species (Edexcel IGCSE Biology: Double Science)

• Variation is defined as differences between individuals of the same species
• Variation can be divided into two types depending on how you are able to group the measurements:
  • Continuous variation is when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale
    • Examples include height, mass, finger length etc. where there can be many ‘in-between groups

  • Discontinuous variation is when there are distinct differences for a characteristic
    • For example, people are either blood group A, B, AB or O; are either male or female; can either roll their tongue or not - there are no ‘in-betweens'

• When graphs of these data are plotted, continuous variation gives smooth bell curves (a result of all the small degrees of difference), whereas discontinuous gives a ‘step–like’ shape

Height is an example of continuous variation which gives rise to a smooth bell-shaped curve when plotted as a graph

Blood group is an example of discontinuous variation which gives rise to a step-shaped graph