Variation Within Species
- Variation is defined as differences between individuals of the same species
Phenotypic Variation
- Phenotypic variation is the difference in features between individuals of the same species
- Phenotypic variation can be caused in two main ways:
- It can be genetic – controlled entirely by genes (this is called genetic variation)
- It can be environmental – caused entirely by the environment in which the organism lives
- Or it can be due to a combination of genes and the environment
Genetic Variation
- Examples of genetic variation in humans include:
- blood group
- eye colour
- sex
- ability to roll tongue
- whether ear lobes are free or fixed
Free or fixed ear lobes diagram
Whether earlobes are attached (lobeless) or free (lobed) is an example of genetic variation
Environmental Variation
- Characteristics of all species can be affected by environmental factors such as climate, diet, accidents, culture and lifestyle
- In this instance ‘environmental’ simply means ‘outside of the organism’ and so can include factors like climate, diet, culture, lifestyle and accidents during lifetime
- Examples include:
- An accident may lead to scarring on the body
- Eating too much and not leading an active lifestyle will cause weight gain
- Being raised in a certain country will cause you to speak a certain language with a certain accent
- A plant in the shade of a big tree will grow taller to reach more light
Genetic and Environmental Causes
- Discontinuous variation is usually caused by genetic variation alone
- Continuous features often vary because of a combination of genetic and environmental causes, for example:
- tall parents will pass genes to their children for height
- their children have the genetic potential to also be tall
- however if their diet is poor then they will not grow very well
- therefore their environment also has an impact on their height
- Another way of looking at this is that although genes decide what characteristics we inherit, the surrounding environment will affect how these inherited characteristics develop