Individuals belonging to a particular species are never identical. They all differ from each other in many ways. This is called variation.

In the case of animal species, there can be individuals who are tall and others who are short, fat or thin, strong or weak, ones with long legs and others with short, as well as everything in between.

There is also variation in characteristics difficult to detect with the naked eye, such as blood type, resistance to disease, quality of the senses, aggressiveness, etc.

In the case of plants, members of the same species can vary in the size and shape of leaves, the taste of the fruit, the size and color of the seed, the thickness of the stem, their resistance to changes in temperature, etc.

In all populations of any given species, it will always be possible to find individuals who vary with respect to some characteristics. It is said that such a population has variability due to genetic diversity.