Human variability, or human variation, is the range of possible values for any measurable characteristic, physical or mental, of human beings. Differences can be trivial or important, transient or permanent, voluntary or involuntary, congenital or acquired, genetic or environmental. This article discusses variabilities that characterize a person for all or much of his or her lifetime, and are perceived as not purely learned or readily changed (such as religion, language, customs, or tastes). Each person being different is so essential a part of human experience that it is difficult to even imagine a human existence in which other people are identical. Furthermore, the social value put on these differences by the society in which one lives affects every aspect of a person's life.