Changes in human height

Human height is regulated by many factors. Since the development of modern medicine and plentiful nutrient-rich food in the developed world average height has increased dramatically. Nutrition is the most important factor in determining height; and height records from military records and other documents can be used to quite accurately compare nutrition and height in various eras. Evidence has shown that height decreased in Britain in the early nineteenth century, before beginning its long increase around mid-century. Increase in height has not been constant; however. The European Middle Ages was an era of tallness with men of above six feet (1.83 m) considered unremarkable. In Europe human height reached its nadir at the start of the nineteenth century. Until the general rise in human health, as urbanization increased, the accompanying trend was a height decline.

Europeans in North America were far taller than those in Europe in the eighteenth and nineteenth centuries, in fact the tallest in the world. The original indigenous population was also among the tallest populations of the world at the time. However, several nations, indeed many nations in Europe, have now surpassed the US in terms of average stature, particularly the Netherlands and Scandinavian nations. Most markedly is the Netherlands where average height has increased at the greatest rates. For instance: the Netherlands was in the late nineteenth century a land renowned for its short population, but today it has the tallest average in the world with young men averaging 6 ft 0.5 in (1.84 m) tall. The 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. In contrast, average male height in impoverished Vietnam and North Korea^[1] remains very 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. The difference between South Koreans, and even older North Koreans, compared to young North Koreans who grew up during the famine of the 1990s-2000s is extraordinary.

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.

Height is determined by the complex interactive combination of genetics and environment. Genetic potential plus nutrition minus stressors is a basic formula. 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 after which 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 is 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.

Asian populations were once thought to be inherently shorter, but with the increases in height even in East Asian nations such as Japan and South Korea as diet changes it now seems that humans as a species probably possess a roughly similar genetic height potential (excluding permutations like the Pygmies), and that thus a predictive genotypic basis for height differentiation has not yet evolved.

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; however, too much work or anaerobic and muscular development can impede growth or even induce premature cessation, or can induce premature closing of the growth plates (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 is a somewhat sexually dimorphic trait, with women generally having a longer leg to body ratio than men. Height is also attained from growth of the spine, and conversely to women's longer leg ratio, men have a longer torso ratio. 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 variance in height between populations and across time is largely changes in leg length. The remainder of height consists of the cranium. Height is obviously sexually dimorphic and statistically it is normally distributed.

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, which the 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.

Role of an individual's height

Height has important social ramifications. For men, shortness is often a disadvantage with men being less likely to respect short men and women generally finding them less attractive. Women in most cultures tend to specifically prefer tall men as partners. It is especially important to them (and also to most men) that the man be taller than the woman. Taller politicians have a tendency to win elections. Studies have found taller men marry earlier and earn higher wages. Others have found that most CEOs and upper management individuals are taller than average. (However, some studies suggest that it is not adult height but rather the usually correlated height during adolescence that is the determinative factor, suggesting that it is the impact of height on self-image that is operative. Yet other studies have found no significant difference in self-image and social status for shorter adolescent boys.) It is almost the opposite for women where tallness may be seen as unattractive to some men. Still, it is not uncommon to see 6 ft (1.83 m) tall female supermodels, where the field has other imperatives than real-life sexual attraction. Discrimination based on height is known as heightism.

Tallness is correlated to better cardio-vascular health and overall better than average health and longevity. However height may be not causative of better health and longevity.

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 well above average in height compared to the general population. In some sports, such as horse riding, auto racing, and gymnastics, a smaller frame is more valuable.

In other sports, the role of height is specific to particular positions. For example, in soccer, a tall goalkeeper is at an advantage because he has a greater armspan and can more easily jump higher, so one will rarely, if ever, see a short goalkeeper in professional soccer. 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 out jump shorter defensive backs to catch high balls. By contrast, shorter running backs are often thought to be at an advantage because they can get "lost" behind large offensive linemen, making it harder for defenders to react at the beginning of a play, but more importantly a shorter running back has a lower center of gravity than a taller person of the same weight, making it harder for defenders to tackle him. Thus, in the NFL and in NCAA Division I football, running backs under 6'0" are more common than running backs over 6'3". Former Heisman Trophy winner and NFL All-Pro 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.

Giraffes are one of the world's tallest mammals. They are well known for their long necks, long legs, and spotted patterns. Giraffes have small "horns" or knobs on top of their heads that grow to be about five inches long. These knobs are used to protect the head in fights.

Clothes make the man. Naked people have little or no influence on society.

Mark Twain (1835 - 1910)