- Human variability
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.
ources of human variability
biological inheritance, shaped by
mutations, allelic differences
**prenatal environment and fetal "programming"
**artificial or cultural selection
quality of lifeand health care
pollutionand toxinexposure and other stressors
**family environment and upbringing (especially before age 5)
***child abuse and neglect
**accidental, industrial or intentional injury,
mutilation, or change of the body
While nearly all of the variables listed above are at least partially determined or affected by genetic factors, few of them are controlled by simple
Mendelian inheritance. Most are polygenicor are determined by a complex combination of genes and early environment. Essentially, genes provide proclivities and potentialities continuously involving feedback mechanisms with the environment throughout life, but especially during prenatal and early childhood.
Many genetic differences (polymorphisms) have little effect on health or reproductive success, but serve to statistically distinguish one population from another. Researchers in the field of
population geneticshave been using these to elucidate ancient migrations and relationships between population groups.
Another purely genetic set of individual differences are the
blood types and immune types we all carry. While some may carry mild advantages or disadvantages in terms of risks of particular diseases, the primary life-or-death significance comes when we attempt to transfer blood or organs from one person to another. Our immune systemis designed to recognize these human differences with great sensitivity and enforce our individuality.
ocial significance and valuation of human variability
Human beings rarely give all possible values for a given parameter of the same value, though not all people agree on the values or relative rankings. Examples of differences which may be given different values in different societies include darker/lighter skin color or thinness/fatness. Local valuation may affect social standing, reproductive opportunities, or even survival.
Possession of above average amounts of some abilities is valued by most societies: ability to learn; musical aptitude; strength, endurance, agility; resilience.
Each individual's distinctive differences, even the negatively valued ones, are usually considered an essential part of self-identity. Membership or status in a social group may depend on having specific values for certain attributes. It is not unusual for people to deliberately try to amplify or exaggerate differences, or to conceal or minimize them, for a variety of reasons. Examples of practices designed to minimize differences include
hair straighteningor skin bleaching, plastic surgery, orthodontia, and growth hormone treatmentfor extreme shortness. Conversely, male-female differences are enhanced and exaggerated in most societies.
These differences may vary or be distributed in various ways. Some, like height for a given sex, vary in close to a "normal" or Gaussian distribution. Some characteristics (e.g., skin color) vary continuously in a population, but the continuum may be socially divided into a small number of distinct categories. Some characteristics vary bimodally (for example,
handedness), with fewer people in intermediate categories.
Different human societies may assign different values to various differences. The obvious examples are race and sex, while handedness has a much weaker value difference, but nearly all human differences will have social value dimension. In some societies, such as the
United States, circumcisionis practiced on a majority of males, as well as sex reassignmentof intersexinfants, with substantial emphasis on cultural norms.
Much social controversy surrounds the assigning or distinguishing of some categories, with variation between groups in a society or between societies as to the degree to which a difference is part of a person's "essential" nature or is partly a socially constructed attribution. For example, in the United States and Europe there has been a centuries-long debate over whether sexual orientation is an essential part of one's nature (the "essentialist" position), or a result of mutually reinforcing social perceptions and behavioral choices (the "constructivist" perspective). Other cultures may not even understand the controversy.
Controversy also surrounds the boundaries of "wellness", "wholeness," or "normality." In some cultures, physical imperfections can exclude one from religious service. In western culture there has been large-scale renegotiation of the social significance of variations which reduce the ability of a person to do one or more functions. Laws have been passed to alleviate the reduction of social opportunity available to those with disabilities. The concept of "differently abled" has been pushed by those persuading society to see limited incapacities as a human difference of less negative value.
When an inherited difference of body structure or function is severe enough, it is termed a
genetic disease, but even this classification has fuzzy edges. There are many instances in which the degree of negative value of a human difference depends completely on the social or physical environment. For example, in a society with a large proportion of deafpeople (as Martha's Vineyardin the 19th century), it was possible to deny that deafness is a disability. Another example of social renegotiation of the value assigned to a difference is reflected in the controversy over management of ambiguous genitalia, especially whether abnormal genital structure has enough negative consequences to warrant surgical correction.
Furthermore, many genetic traits may be advantageous in certain circumstances and disadvantageous in others. Being a
heterozygoteor carrier of the sickle-cell diseasegene confers some protection against malaria, apparently enough to maintain the gene in populations of malarial areas. In a homozygous dose it is a significant disability.
The extreme exercise of social valuation of human difference is in the definition of "human." What difference is great enough to assign an individual "nonhuman" status, in the sense of withholding our identification, charity, and social participation? This can change enormously between cultures and over time. For example, nineteenth century European and American ideas of race and
eugenicsculminated in the attempts of the Nazi-led German society of the 1930s to deny not just reproduction, but life itself to a variety of people with "differences" attributed in part to biologic characteristics. Western society's revulsion to this contributed to a considerable readjustment of valuation of differences.
Contemporary controversy continues over "what kind of human" is a fetus or child with a significant disability. On one end are people who would argue that
Down's syndromeis not a disability but a mere "difference," and on the other those who consider such a calamity as to assume that such a child is better off "not born". In India and China, being female is widely considered such a negatively valued human difference that similar decisions are made by the hundreds of thousands.
Acknowledgement and study of human differences does have a wide range of uses, such as tailoring the size and shape of manufactured items. See
Common human variations
Human genetic variation
Sex( Male, female, see also intersex)
eye coloring, complexion
Hair color, baldness, hirsutism, body hair
Supernumerary body part(such as Polydactylism, Supernumerary nipples, Hyperdontia) or missing body parts (such as Hypogenesis)
**Cleft lip and Cleft palate
*Body shape and size
dwarfism, Little people
Body type/ Somatotype, thinness, obesity
Motor skills, handedness, dexterity
Amputation, loss of limbs or limb function
Blindness, color blindness
Deafness, tone deafness
Diseases and defects of other organ systems
*Other aspects of
human physical appearance
**attractiveness (highly subjective, variable, and impermanent)
**acquired variability in physical appearance
*Psychological and personality traits
**Intelligence, spatial aptitude
Temperament, introversion, extroversion, impulsiveness, risk-taking
Developmental disability, cognitive disability, social disability
Emotional stability, mental illness
* [http://www.linfo.org/human_variability.html Human Variability: A Brief Introduction]
Wikimedia Foundation. 2010.
Look at other dictionaries:
Human (disambiguation) — Human may refer to *any member of the Homo genus (since ca. 2.5 million years) **Human taxonomy ** Homo sapiens (modern humans), the only surviving species of Homo . ***archaic Homo sapiens (since ca. 200,000 years) *** Homo sapiens idaltu (ca.… … Wikipedia
Variability — The term , the state or characteristic of being variable , may be applied to many different subjects:*Solar van *Human variability *Genetic variability *Heart rate variability *Spatial variability *Statistical variability *Climate variability … Wikipedia
Human height — Tall redirects here. For other uses, see Tall (disambiguation). Human height is the distance from the bottom of the feet to the top of the head in a human body standing erect. When populations share genetic background and environmental factors,… … Wikipedia
Human reliability — is related to the field of human factors engineering, and refers to the reliability of humans in fields such as manufacturing, transportation, the military, or medicine. Human performance can be affected by many factors such as age, circadian… … Wikipedia
Human genetic variation — is the natural variation in gene frequencies observed between the genomes of individuals or groups of humans. Variation can be measured at both the individual level (differences between individual people) and at the population level, i.e.… … Wikipedia
Human mortality from H5N1 — or the human fatality ratio from H5N1 or the case fatality rate of H5N1 refer to the ratio of the number of confirmed human deaths resulting from confirmed cases of transmission and infection of H5N1 to the number of those confirmed cases. For… … Wikipedia
Human Race — Human Race † Catholic Encyclopedia ► Human Race Mankind exhibits differences which have been variously interpreted. Some consider them so great that they regard the varieties of the human race as distinct species; others maintain the… … Catholic encyclopedia
human development — ▪ biology Introduction the process of growth and change that takes place between birth and maturity. Human growth is far from being a simple and uniform process of becoming taller or larger. As a child (child development) gets bigger,… … Universalium
Human brain — The human brain controls the central nervous system (CNS), by way of the cranial nerves and spinal cord, the peripheral nervous system (PNS) and regulates virtually all human activity.Cite web|url=http://encarta.msn.com/encyclopedia… … Wikipedia
human disease — Introduction an impairment of the normal state of a human being that interrupts or modifies its vital functions. health versus disease Before human disease can be discussed, the meanings of the terms health, physical fitness, illness … Universalium