Variation

No two living things are exactly the same, not even identical twins. These differences are called variation. Some of it is passed on from parents in our genes, some comes from where and how we live, and most features come from both. Scientists measure variation and use graphs to see its patterns.

Key facts

• Variation is the differences between living things: between different species, and between individuals of the same species.
• A species is a group of organisms that can breed together to produce fertile offspring.
• Genetic (inherited) variation comes from the genes passed on by parents: blood group, natural eye colour, natural hair colour.
• Environmental variation is caused by surroundings and lifestyle: scars, language, accent, tattoos. Many features, such as height and body mass, are affected by both genes and the environment.
• Continuous variation can take any value in a range (height, mass, hand span, leaf length). Show it on a histogram or line graph; it often makes a bell-shaped curve.
• Discontinuous variation falls into a few separate groups (blood group, tongue rolling, attached or free earlobes). Show it on a bar chart.
• Mutations, changes in DNA, create new variation. Most have no effect, a few are harmful and very few are helpful.

Worked examples