What is Definition of Continuous Variation

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Types of variation

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Key points

• Variation is the differences between individuals of the same species, caused by genetic and environmental factors.
• Surveys into variation give data that are continuous, which means to come in a range, or discontinuous, which means to come in groups.

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Learn about the different types of variation

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Every crisp is unique and thanks to variation, every organism is unique too.

Due to genetic and environmental factors, members of the same species will have different characteristics or variation. We measure and visualise variation based on whether it is continuous or discontinuous.

Discontinuous variation refers to things like eye colour or blood group, which have a limited number of possible values. In other words, a person's blood can be A, B, AB or O, but it can't be anything in between. So we can simply count how many in our sample are in each group, which we can represent well with a bar graph.

Continuous variation refers to characteristics like weight or height, which change gradually. A person's height could measure any value in between the shortest and tallest person in the world. Line graphs show continuous variation well and often, but not always turn out to be bell shaped because most specimens have close to average characteristics.

Thanks to variation the world is full of interesting, unique organisms, just like my bowl is full of unique crisps. Well it was anyway.

Variation

is all the differences that exist in a population of the same species. These differences are caused by:

• Genetic variation - these are differences between individuals that are inherited from parents, such as the colour of your eyes, hair and skin.
• Environmental variation - these are differences between individuals that are not inherited but caused by the environment that the organism lives in, including scars and tattoos.
• Genetic and environmental variation - differences between individuals that are caused by both genetic and environmental factors, such as height and weight.

Data on variation is collected by surveying the population. This data can be described as either continuous variation or discontinuous variation. It is important to remember that these are not the causes of variation, which are described above, but how we analyse the results of the surveys.

Continuous variation

Surveys of give us results that come in a range. 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 this is continuous variation. For example, you can be 150 cm tall, 151 cm tall, or any height in between this - if you had a ruler that could measure small enough values.

So, a characteristic that changes gradually over a range of values shows continuous variation. Examples of such characteristics are:

• height
• arm span
• weight

Results from surveys of continuous variation are presented in line graphs or bar charts with a drawn through them. If you record the heights of a group of people and draw a graph of your results, it usually looks something like this:

A bar chart to represent variation in height

Normal distribution

Surveys of continuous variation often give us results in a characteristic shape seen in the green line on the graph above. If there are fewer readings at either ends of the scale and far more in the middle, we see a of . The more people you measure and the smaller the categories you use, the closer the results will be to this shape.

Discontinuous variation

Surveys of give us values that come in groups rather than a range. Human blood groups are an example of discontinuous variation. In the ABO blood group system, only four blood groups are possible - A, B, AB or O. You cannot have a blood group in between these four groups, so this is discontinuous variation.

Here are some examples:

• blood group
• eye colour

Results from surveys of discontinuous variation are presented in charts. These is no line of best fit drawn because the values on the x-axis - blood groups in the graph below - could be placed in any order. If you record the blood groups of a group of people and draw a graph of your results, it usually looks something like this:

A bar chart to represent the frequency of each blood group in the population

More examples

Continuous variation	Discontinuous variation
Height	Blood group
Weight	Hand used to write with
Arm span	Eye colour
Head circumference at birth	Ability to roll tongue

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Source: https://www.bbc.co.uk/bitesize/topics/zpffr82/articles/z6j66g8

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