Some variation within a species is inherited, and some variation is due to the environment.
Children usually look a little like their father, and a little like their mother, but they will not be identical to either of their parents. This is because they get half of their DNA and inherited features from each parent.
Each egg cell and each sperm cell contains half of the genetic information needed for an individual. When these join at fertilisation a new cell is formed with all the genetic information needed for an individual.
Here are some examples of inherited variation in humans:
Gender is inherited variation too, because whether you are male or female is a result of the genes you inherited from your parents.
Characteristics of animal and plant species can be affected by factors such as:
For example, you will become heavier if you eat too much food, and you will become lighter if you eat too little. A plant in the shade of a big tree will grow taller as it tries to reach more light.
Variation caused by the surroundings is called environmental variation. Here are some other examples of features that show environmental variation:
Some features vary because of a mixture of inherited causes and environmental causes. For example, identical twins inherit exactly the same features from their parents. However, if you take a pair of twins, and twin 'A' is given more to eat than twin 'B', twin 'A' is likely to end up heavier. Weight and height are common examples of characteristics that are influenced by both genetic and environmental factors.