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

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
• hand span

Height ranges from that of the shortest person in the world to that of the tallest person. Any height is possible between these two extremes. So it is called continuous variation.

The shape of this graph is typical of a characteristic with continuous variation. The more people you measure, and the smaller the range of categories you use, the closer the results will be to the curved line. The shape seen in this graph is called a bell shaped curve, and is the result of a variable being normally distributed.

Discontinuous variation

A characteristic of any species with only a limited number of possible values shows discontinuous variation. For example:

• gender (male or female)
• eye colour
• blood group

Human beings have one of four blood groups, A, B, AB or O. There are no values in between (intermediate values), so this shows discontinuous variation.