Causes of variation

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Key points

  • The differences in characteristics between individuals of the same is called .

  • Some variation is passed on from parents to offspring, via during reproduction. This is variation.

  • Some variation is the result of differences in the surroundings, or what an individual does. This is called environmental variation.


Humans, dogs and goldfish are examples of species.

Different species have different characteristics from each other. For example, dogs have tails and humans do not. Dogs have fur, but goldfish have scales.

The individual members of a species also have differences in characteristics. For example, humans have different coloured eyes, and dogs have different length tails. This means that no two members of a species are identical.

The differences between the individuals in a species is called variation.

Variation helps a species to survive, by causing individuals of a species to be genetically and physically different.


A guide dog breeder explains the effect of variation on his puppies

Genetic and environmental variation

Characteristics in an individual organism are caused by both genetic and environmental variation.

For example, the weight of a dog is caused partly by its genes - inherited - and partly by what it eats - environmental. The height of a sunflower is caused partly by its genes and partly by how much light and water it gets.

Genetic onlyEnvironmental onlyGenetic and environmental
Eye colourTattoosHeight
Blood groupScarsWeight
Attached ear lobesLanguage spokenHuman's hair colour - can lighten in summer or can be dyed
Animal's fur colourColour of hydrangea flower - blue in acid soil, pink in alkalineSize of plant

Quiz - Genetic or environmental?

Benefits of variation

If all the individuals of a species were genetically identical they would be vulnerable to the same diseases. If this were the case a single disease could wipe out an entire species.

As a result of their genes, some individuals of a species might have better camouflage, or be able to run faster. These individuals are more likely to survive. This is called the survival of the fittest.

The members of a species that survive may reproduce. Their offspring are likely to have the desirable characteristics of their parents. This is how species change in evolution.

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Quiz - Variation