Variation in biology refers to any difference between individuals in a species or groups of organisms of any species. It can be caused by genetic differences, environmental factors, or a combination of both. There are two main causes of variation:

• Inherited causes of variation: This type of variation results from the passage of genetic information from parents to offspring. Examples include eye color, hair color, and lobed or lobeless ears.

• Environmental causes of variation: This type of variation is caused by environmental factors such as diet, climate, and lifestyle. Examples include a persons skin color, hair color, and freckles.

Variation can be classified as either continuous or discontinuous. Continuous variation smoothly grades between two extremes, with the majority of individuals at the center, such as height in human populations. Discontinuous variation is composed of well-defined classes, such as blood groups in humans.

Variation is important in biology because it enables organisms to adapt to changing environments, forms the raw material for evolution, and helps organisms face the struggle for existence in a better way.