Adult human height generally varies little between people compared to other anthropometric measures. Exceptional height (variation from the average of around 20%) is usually due to gigantism or dwarfism. Adult height for one sex in a particular ethnic group follows more or less a Gaussian distribution.
Changes in human height
In Western countries, height has varied significantly in the past few millennia. During the Industrial Revolution, Westerners were three inches shorter than their ancestors from the 11th century.[1] The European Middle Ages was an era of tallness with men of above six feet (1.83 m) considered unremarkable. Average height decreased again in Britain in the early nineteenth century, then began to rise again mid-century.
In the 18th and 19th centuries, Europeans in North America were far taller than those in Europe - in fact they were the tallest in the world. The original indigenous population of Plains Indians was also among the tallest populations of the world at the time.[2] Several nations, including many nations in Europe, have now surpassed the US, particularly the Netherlands, and the Scandinavian nations.
The Netherlands was in the late nineteenth century a land renowned for its short population, but today it has the 2nd tallest average in the world,[3] with young men averaging 6 ft (1.83 m) tall and only shorter than the peoples of the Dinaric Alps (Serbia, Montenegro, Bosnia), where males average 6 ft 1.08 in (1.856 m) tall. The Dinarians and Dutch are now well known in Europe for extreme tallness. The increase has been so dramatic that various things have been redesigned to fit the much taller frames.[citation needed]
Average male height in impoverished Vietnam and North Korea[4] remains comparatively small at 5 ft 4 in (1.63 m) and 5 ft 5 in (1.65 m) respectively. Currently, young North Korean males are actually significantly shorter. This contrasts greatly with the extreme growth occurring in surrounding Asian populations with correlated increasing standards of living. Young South Koreans are about 3 inches (8 cm) taller than their North Korean counterparts, on average. There is also an extreme difference between older North Koreans and young North Koreans who grew up during the famines of the 1990s-2000s.
[edit] Determinants of growth and height
An example of human growth velocity under optimal conditions (Courtesy: Richard Steckel)The study of human growth is known as auxology. Growth and height have long been recognized as a measure of the health and wellness of individuals, hence part of the reasoning for the use of growth charts. For individuals, as indicators of health problems, growth trends are tracked for significant deviations and growth is also monitored for significant deficiency from genetic expectations. Genetics is a major factor in determining the height of individuals, though it is far less influential in regard to populations. Average height is increasingly used as a measure of the health and wellness (standard of living and quality of life) of populations. Attributed as a significant reason for the trend of increasing height in parts of Europe is the egalitarian populations where proper medical care and adequate nutrition are relatively equally distributed. Changes in diet (nutrition) and a general rise in quality of health care and standard of living are the cited factors in the Asian populations. Average height in the United States has remained essentially stagnant since the 1950s. Severe malnutrition is known to cause stunted growth in North Korean, portions of African, certain historical European, and other populations. Diet (in addition to needed nutrients; such things as junk food and attendant health problems such as obesity), exercise, fitness, pollution exposure, sleep patterns, climate (see Allen's rule and Bergmann's Rule for example), and even happiness (psychological well-being) are other factors that can affect growth and final height.
Sir Francis Galton's (1889) data showing the relationship between offsping height (928 individuals) as a function of mean parent height (205 sets of parents). Heritability (h^2) is equal to the slope of the regression line, 0.57.Height is determined by the complex interactive combination of genetics and environment. Genetic potential plus nutrition minus stressors is a basic formula. Genetically speaking, the heights of mother and son and of father and daughter correlate, suggesting that a short mother will more likely bear a shorter son, and tall fathers will have tall daughters. [2] Humans grow fastest (other than in the womb) as infants and toddlers (birth to roughly age 2) and then during the pubertal growth spurt. A slower steady growth velocity occurs throughout childhood between these periods; and some slow, steady, declining growth after the pubertal growth spurt levels off is common. These are also critical periods where stressors such as malnutrition (or even severe child neglect) have the greatest effect. Conversely, if conditions are optimal then growth potential is maximized; and also there is catch-up growth — which can be significant — for those experiencing poor conditions when those conditions improve.
Moreover, the health of a mother throughout her life, especially during her critical periods, and of course during pregnancy, has a role. A healthier child and adult develops a body that is better able to provide optimal prenatal conditions. The pregnant mother's health is important as gestation is itself a critical period for an embryo/fetus, though some problems affecting height during this period are resolved by catch-up growth assuming childhood conditions are good. Thus, there is an accumulative generation effect such that nutrition and health over generations influences the height of descendants to varying degrees.
The precise relationship between genetics and environment and exact role of genetics itself is complex and uncertain. Human height is both of moderately high phenotypic plasticity and is highly heritable. Height is a multigenic trait. There are substantial relationships in the heights among biological families; the heights of parents and family are a good predictor for the height of their children. Environmental influences are most pronounced if they are highly favorable or unfavorable to growth, especially when occurring during critical periods and when continuing multigenerationally. Genetic profile (genotype) provides potentialities or proclivities which interact with environmental factors throughout the period of growth resulting (phenotype) in final adult height. Essentially, the developing body devotes energy to growth after other bodily functions are satisfied.
[edit] Ethnicity and height
Asian populations were once thought to be inherently shorter, but with the increases in height in East Asian nations such as China and South Korea as diet changes, they have become taller. [5] Many Asians still are on a diet that depresses growth.
Diet is also a reason of why Asians are short. A typical Asian diet contains little calcium, little protein, and accommodates a relatively large amount of soybean products, which contain isoflavones, a type of phytoestrogen that acts like a female hormone. [6] [7] [8] Asians take in little iron, Vitamin A and Vitamin D, which causes growth retardation. [9][10] [11] [12] [13] [14] [15]
It now seems that humans as a species probably possess a roughly similar genetic height potential[citation needed] (excluding permutations like the Pygmies), and that thus a predictive genotypic basis for height differentiation has not yet evolved.
[edit] Process of growth
Growth in stature, determined by its various factors, results from the lengthening of bones via cellular divisions chiefly regulated by somatotropin (human growth hormone (hGH)) secreted by the anterior pituitary gland. Somatotropin also stimulates the release of another growth inducing hormone insulin-like growth factor 1 (IGF-1) mainly by the liver. Both hormones operate on most tissues of the body, have many other functions, and continue to be secreted throughout life; with peak levels coinciding with peak growth velocity, and gradually subsiding with age after adolescence. The bulk of secretion occurs in bursts (especially for adolescents) with the largest during sleep. Exercise promotes secretion. (indeed, adolescents who take steroids can experience stunted growth). A positive net nutrition is also important, with proteins and various other nutrients especially important.
The majority of linear growth occurs as growth of cartilage at the epiphysis (ends) of the long bones which gradually ossify to form hard bone. The legs compose approximately half of adult human height, and leg length is a somewhat sexually dimorphic trait. Height is also attained from growth of the spine, and contrary to popular belief, men are the "leggier" gender with a longer leg to torso ratio, conversely to women's longer torso to leg ratio. (The illusion of the proportion being the other way around is caused by fatty deposits placed high on women's hips.) Some of this growth occurs after the growth spurt of the long bones has ceased or slowed. The majority of growth during growth spurts is of the long bones. Additionally, the variation in height between populations and across time is largely due to changes in leg length. The remainder of height consists of the cranium. Height is obviously sexually dimorphic and statistically it is more or less normally distributed, but with heavy tails.
[edit] Height abnormalities
Most intra-population variance of height is genetic. Short stature and tall stature are usually not a health concern. If the degree of deviation from normal is significant, hereditary short stature is known as familial short stature and tall stature is known as familial tall stature. Confirmation that exceptional height is normal for a respective person can be ascertained from comparing stature of family members and analyzing growth trends for abrupt changes, among others. There are, however, various diseases and disorders that cause growth abnormalities. Most notably, extreme height may be pathological, such as gigantism (very rare) resulting from childhood hyperpituitarism, and dwarfism which has various causes. Rarely, no cause can be found for extreme height; very short persons may be termed as having idiopathic short stature. The Food and Drug Administration (FDA) in 2003 approved hGH treatment for those 2.25 standard deviations below the population mean (approximately the lowest 1.2% of the population). An even rarer occurrence, or at least less used term and recognized "problem", is idiopathic tall stature.
If not enough growth hormone is produced and/or secreted by the pituitary gland, then a patient with growth hormone deficiancy can undergo treatment. This treatment involves the injection of pure growth hormone into thick tissue to jump-start the growth process.
[edit] Role of an individual's height
Tallness has been suggested to be associated with better cardio-vascular health and overall better-than-average health and longevity (Njolstad et al. 1996,[16] McCarron et al 2002[17]). However, height may not be causative of better health and longevity (Miura et al. 2002). Other studies have found no association, or suggest that shorter stature is associated with better health (Samaras & Elrick, 1999[18]). On the other hand, being excessively tall can cause various medical problems, including cardiovascular issues, due to the increased load on the heart to supply the body with blood, and issues resulting from the increased time it takes the brain to communicate with the extremities. For example, Robert Wadlow, the tallest man known to verifiable history, developed walking difficulties as his height continued to increase throughout his life. In many of the pictures of the later portion of his life, Wadlow can be seen gripping something for support. Late in his life he was forced to wear braces on his legs and to walk with a cane, and he died after developing an infection in his legs because he was unable to feel the irritation and cutting caused by his leg braces (it is important to note that he died in 1940, before the widespread use of modern antibiotics). Height extremities of either excessive tallness or shortness can cause social exclusion and discrimination for both men and women (heightism).
Epidemiological studies have also demonstrated a positive correlation between height and intelligence. The reasons for this association appear to include that height serves as a biomarker of nutritional status or general mental and physical health during development, that common genetic factors may influence both height and intelligence, and that both height and intelligence are affected by adverse early environmental exposures.
Main article: Height and intelligence
In addition, an individual's height can be largely a part of what social clique, or group that they fall in to, though this is usually associated with pre-teens and teenagers. For example, in some schools, students on the basketball team might be "cool", and those with short stature wouldn't likely make the team. Therefore, in some cases, this could contribute to them being classified as "weak" or "uncool", which can be detrimental to that particular individual's self-esteem.
This can also sometimes be translated over into the corporate world. Individuals with short stature can sometimes appear to not have any leadership ability or power, since some people might not take them seriously due to their diminutive nature. However, this is not always the case with most employers[citation needed].
[edit] The role of height in sports
Height often plays a crucial role in sports. For most sports, height is useful as it affects the leverage between muscle volume and bones towards greater speed of movement. It is most valuable in sports like basketball and volleyball, where the "short" players are almost always well above average in height compared to the general population. In some sports, such as horse racing, auto racing, diving, figure skating and gymnastics, a smaller frame is more valuable.
In other sports, the role of height is specific to particular positions. For example, in Football, tall goalkeepers have an advantage because they have greater armspans and can jump higher easily, so one will rarely, if ever, see a short goalkeeper in professional football. However, shorter goalkeepers will have an easier time reaching low shots as they can reach the ground fractionally sooner than taller keepers. In attacking and wide posistions in football height is not always important with some of the best players in the world (i.e. Roberto Carlos and Maradona) being shorter then average, although height positions just as centre-back benifit from tall players. Similarly, in cricket, some good players like Don Bradman and Sachin Tendulkar are/were short. In rugby union, lineout jumpers are usually the tallest players on the pitch, as this increases their chance of winning clean ball, whereas scrum-halves are usually relatively short. In American football, a tall quarterback is at an advantage because it is easier for him to see over the heads of large offensive and defensive linemen while he is in the pocket on a pass play. Tall wide receivers are at an advantage because they can outjump shorter defensive backs to catch high balls. By contrast, shorter running backs are at an advantage because at a lower center of gravity, with increased stride frequency (and thus acceleration), are harder to effectively bring down. In addition, they can get "lost" behind large offensive linemen, making it harder for defenders to react at the beginning of a play. Thus, in the NFL and in NCAA Division I football, running backs under 6 ft 0 in (1.83 m) are more common than running backs over 6 ft 3 in (1.91 m). Former Heisman Trophy winner and Pro Football Hall of Famer Barry Sanders, thought by some to be the greatest running back in history, is a classic example of a running back with an extraordinarily low center of gravity—at only 5 ft 7 1/2 in (1.71 m). However, Jim Brown, another player often considered the greatest running back of all time, was more than 6 ft 2 in (1.88 m) tall, helping display the benefits conferred by the greater leverage which height provides. In baseball, pitchers tend to be taller than position players, since having longer arms tends to mean greater arm speed and harder throws, but while batting means a larger strike zone