Variation refers to the differences between individuals of the same species. There are two causes of variation in a species:
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
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.
Below are some other examples of environmental causes of variation:
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.