Continuous and discontinuous variation

Some of the features of the different organisms in a species show continuous variation, and some features show discontinuous variation.

Continuous variation

Human height is an example of continuous variation. It ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these values. So it is continuous variation.

For any species a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are:

  • height
  • weight

If you record the heights of a group of people and draw a graph of your results, it usually looks something like this:

Chart is roughly symmetrical, with fewer people in the smaller height categories (such as up to 129cm) and fewer people in the taller height categories such as over 175cm. The category with the greatest number of people is 150-154cmA bar chart to represent variation in height

The more people you measure, and the smaller the categories you use, the closer the results will be to the curved line. This shape of graph is typical of a feature with continuous variation. Weight would give a graph similar in shape to this.

Discontinuous variation

A characteristic of any species with only a limited number of possible values shows discontinuous variation. Human blood group is an example of discontinuous variation. In the ABO blood group system, only four blood groups are possible (A, B, AB or O). There are no values in between, so this is discontinuous variation.

Here are some examples:

  • blood group
  • gender (male or female)
  • eye colour
Chart shows 0 is the most common blood group at over 45% of the population. Nexy is A, at around 40%. Third is B with just under 10%, and finally, under 5% of the population have the blood group ABA bar chart to represent the frequency of each blood group in the population
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