Variation is ubiquitous, all organisms exhibit SOME variation
Look around the classroom and you will immediately notice a great deal of variation among members of this class.
Some of this variation is morphological: hair color, height, eye color, etc..
Some is behavioral: preference for certain foods, knowledge of languages, choice of clothing, etc..
For centuries, biologists have sought an explanation for this variation.
Much of this variation has its basis in our genes, a fact that is of tremendous biological significance.