Variation refers to the differences between individuals of the same species. There are two causes of variation in a species:

  • Genetic causes
  • Environmental causes
  • A combination of genetic and environmental causes

Genetic Causes

We will inherit some alleles from our father and some from our mother. This is why we will look a bit like each parent but not identical to either. The alleles we inherit from our parents control many aspects of our phenotype. For example

  • Skin colour
  • Eye colour
  • Hair colour
  • Blood group

Environmental Causes

There is also some variation within a population of a species which is caused by the environment. For example, when a plant is grown under good conditions required for growth (e.g. sufficient sunlight, water and nutrients), they grow luscious and green.

When the same plant is grown under conditions of less sunlight, water or nutrition, the plants grow slowly.

Variation in plant growth due to an environmental change (light) in the environment.

Below are some other examples of environmental causes of variation:

  • Accidents can cause scars
  • Muscle strength can increase by exercising
  • If you live in a particular country, you may learn the language or develop an accent

Combination of Genetic and Environmental Causes

Some variation is caused by a combination of genes and the environment. For example, some people have alleles which make them more likely to grow taller. However, if their diet is poor, they will not grow very well, so they will not reach their growth potential. This means that their height is a combination of genetics and the environment.