Molecular biologist Chao-Qiang Lai of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University answers.
This question can be rephrased as: "How much variation (difference between individuals) in height is attributable to genetic effects and how much to nutritional effects?" The short answer to this question is that about 60 to 80 percent of the difference in height between individuals is determined by genetic factors, whereas 20 to 40 percent can be attributed to environmental effects, mainly nutrition. This answer is based on estimates of the "heritability" of human height: the proportion of the total variation in height due to genetic factors.
Human height is a quantitative, or metric, trait, i.e., a characteristic that is measured in quantity, and is controlled by multiple genes and environmental factors. Many studies have estimated the heritability of human height. Often, these studies determine heritability by estimating the degree of resemblance between relatives. One can separate genetic effect from environmental effects by correlating genetic similarity between relatives (twin, siblings, parents and offspring) with their similarity in height. To accurately measure how genetically similar relatives are, one can measure the number of genetic markers they share. For example, Peter M. Visscher of the Queensland Institute of Medical Research in Australia recently reported that the heritability of height is 80 percent, based on 3,375 pairs of Australian twins and siblings. This estimate is considered to be unbiased, as it was based on a large population of twins and siblings and a broad survey of genetic markers. In the U.S., the heritability of height was estimated as 80 percent for white men. These estimates are well supported by another study of 8,798 pairs of Finnish twins, in which the heritability was 78 percent for men and 75 percent for women. Other studies have shown height heritability among whites to be even higher than 80 percent.
Because different ethnic populations have different genetic backgrounds and live in different environments, however, height heritability can vary from one population to another, and even from men to women. In Asian populations, the heritability of height is much lower than 80 percent. For example, in 2004 Miao-Xin Li of Hunan Normal University in China and his colleagues estimated a height heritability of 65 percent, based on a Chinese population of 385 families. In African populations, height heritability is also lower: 65 percent for the population of western Africa, according to a 1978 study by D. F. Roberts, then at Newcastle University in England, and colleagues. Such diversities in heritability are mainly due to the different genetic background of ethnic groups and the distinct environments (climates, dietary habits and lifestyle) they experience.
Heritability allows us to examine how genetics directly impact an individual's height. For example, a population of white men has a heritability of 80 percent and an average height of 178 centimeters (roughly five feet, 10 inches). If we meet a white man in the street who is 183 cm (six feet) tall, the heritability tells us what fraction of his extra height is caused by genetic variants and what fraction is due to his environment (dietary habit and lifestyle). The man is five centimeters taller than the average. Thus, 80 percent of the extra five centimeters, or four centimeters, is due to genetic variants, whereas one centimeter is due to environmental effects, such as nutrition.
Heritability can also be used to predict an individual's height if the parents' heights are known. For example, say a man 175 cm tall marries a woman 165 cm tall, and both are from a Chinese population with a population mean of 170 cm for men and 160 cm for women. We can predict the height of their children, assuming the heritability is 65 percent for men and 60 percent for women in this population. For a son, the expected height difference from the population mean is: 0.65 x [(175 - 170) + (165 - 160)] / 2, which equals 3.25 cm; for a daughter, the difference is 0.6 x [(175 - 170) + (165 - 160)] / 2, which equals 3 cm. Thus, the expected height of a son is 170 + 3.2, or 173.2 cm, and of a daughter 160 + 3, or 163 cm. On the other hand, environmental effects can add 1.75 cm to a son's height: 0.35 x [(175 - 170) + (165 - 160)] / 2, and 2 cm to a daughter's: 0.4 x [(175 - 170) + (165 - 160)] / 2. Of course, these predictions only reflect the mean expected height for each of the two siblings (brothers and sisters); the actual observed height may be different.
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9 Comments
Add CommentBut of course, in the US population "horizontal height" (girth) continues to increase which shows that the "nutrient environment has maximized." This comment is a little "fatecious."
Reply | Report Abuse | Link to thisThis article is misleading and inaccurate. A heritability figure would tell you NOTHING of an individual's genetic versus environmental contribution to his height (or any other trait for that matter). So if you did meet someone who is 6 feet tall "in the street" and you knew the proportion of the variance attributed by genes (actually, that is not the heritability but the heritability squared) you'd still be in the dark as to what proportion of his height above the average for the relevant population is due to genes. This is because the concept of heritability is a property of particular populations, not individuals within populations. As to the calculation to predict the heights of future offspring, it is, at best, a predictor of the *average* heights of potential offspring for the respective gender, not the "expected" height of any one offspring.
Reply | Report Abuse | Link to thisYour statement is misleading and inaccurate likewise. A heritability figure
Reply | Report Abuse | Link to thisallows you to make a probabilistic statement about individual genetic versus environmental contributions. (Refer to Tal (2009) "From Heritability to Probability")
Reply | Report Abuse | Link to thisI think you misunderstood my comment. I implicitly stated that such "probabilistic" predictions were sometimes valid based on heritability.
But that doesn't mean that heritability is a measure of *any individual's* genes vs environment contribution fraction. The problem is that it is by its nature a probabilistic measure of populations, not individuals' characteristics. I was objecting to this statement in the article specifically (which is indeed, misleading and inaccurate as I maintained):
"If we meet a white man in the street who is 183 cm (six feet) tall, the heritability tells us what fraction of his extra height is caused by genetic variants and what fraction is due to his environment (dietary habit and lifestyle)."
We know nothing of this man's specific gene vs environment fraction. To put a specific fraction (80/20) is going behind what the data tells us. That fraction is for the whole white population (in the US).
I think the examples of siblings are too basic and does not show the difference between well-and-mis-fed humans. We can compare Latin American heights according to their quality of life and ethnicity. For instance, Mexicans, Chileans, and Argentines have a similar quality of life and nutrition background. While the non-white population of these countires are: Mexicans, 30% indigenous (not talking about culture) and 60% mestizos; Chileans, 9% indigenous and 39% mestizos; and Argentines, 1% indigenous and 20% mestizos; their overall male height are 164cm, 171cm, and 176 cm.
Reply | Report Abuse | Link to thisWe can also compare similar ethnic countries with different quality of life, like Mexico, Ecuador, and Nicaragua. Mexico has a higher quality of life than Ecuador, and so does Ecuador over Nicaragua. However the three of them are ethnically similar. Their average male heights are 164cm, 163cm, and 161cm.
Reply | Report Abuse | Link to thisHeight Prediction Calculator
Reply | Report Abuse | Link to thishttp://www.etoolsage.com/calculator/Height_Prediction_Calculator.asp?toolsort=1500
The calculator permits the user to calculate adult height of a child, this is a prediction based on their parents' height, and information about the child at present including height,weight and age.
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