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

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

Genetic Causes

We inherit some alleles from our father and some from our mother. This is why we might look somewhat 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

TVariation within a population of a species can also be caused by the environment. For example, when a plant is grown under optimal conditions for growth, such as sufficient sunlight, water and nutrients, it grows lusciously 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 that predispose them to be taller. However, if they have a poor diet, they might not reach their full growth potential. This suggests that height is influenced by both genetics and environmental factors.