Friday, November 4, 2016

Influences on Human Height

An article from the Scientific American answers the question as to whether or not human height is based primarily on genetics or if it based on environmental factors like nutrition.  According to Dr. Chao-Qiang Lai of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, about 60-80% of height is determined by genetic factors.  Around 20-40% can be based on environmental factors.

Heritability of a child's height can be calculated if the heights of the parents are known.  Dr. Lai uses the example of a 175 cm tall man marrying a 165 cm tall woman.  Both individuals are of Chinese descent.  Men of Chinese descent are an average of 170 cm while women of Chinese descent are 160 cm.  This data can be used to calculate the expected heights of their children.  The heritability is assumed for men to be 65% and for women to be 60%.

If the couple were to have a son, the calculation would be: 0.65 x [(175 - 170) + (165 - 160)] /2 = 3.25.  He would be expected to deviate from the population by 3.25.  Therefore, his expected height would be around 173.25 cm.

If the couple were to have a daughter, the calculation would be:  0.65 x [(175 - 170) + (165-160)/2 =3.  She would be expected to deviate from the population average by 3 making her height around 163 cm.

By taking environmental factors into consideration,  Dr. Lai states that environmental effects can influence a child's height by about 1.75-2 cm. This prediction reflects the mean height for each of the siblings while the actual observed height may be different.

Why do different populations of a similar genetic background having differing heritability?  In developed countries, proper nutrition is very common among children and maximizes their growth potential.  In undeveloped countries, it is less common for children to have adequate nutrition resulting in shorter heights on average.

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