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Does genetics explain height differences among Indians?

HOW TALL WILL I BE? While recent research has established the link between income levels and height, experts are de3bating if genetic differences explain adults being taller-than-predicted in Rajasthan and J&K and shorter-than-expected in north-eastern States. A group of Tiwa children en route to school in Karbi Anglong district of Assam. Photo: Ritu Raj Konwar

HOW TALL WILL I BE? While recent research has established the link between income levels and height, experts are de3bating if genetic differences explain adults being taller-than-predicted in Rajasthan and J&K and shorter-than-expected in north-eastern States. A group of Tiwa children en route to school in Karbi Anglong district of Assam. Photo: Ritu Raj Konwar  

Recent research has shown that there is a clear correlation between state domestic product and average height. Yet data on heights — and especially the outlier States — raise the question: are there genetic differences between Indian population groups that could have an impact on height?

Height is of particular interest to demographers, nutritionists and economists. A person whose height-for-age is below two standard deviations less than the median for the reference population is described as “stunted”. According to the 2005-6 National Family Health Survey (NFHS-3), 48% of Indian children under 5 and 45% of children under 3 were stunted; one-third of the world’s stunted children live in India. Stunting is a particularly important indicator because the same nutritional processes that determine a child’s height in the first 24 months also determine his or her cognitive potential, Dean Spears, a visiting economist at the Centre for Development Economics at the Delhi School of Economics, told The Hindu.

In a working paper, economist Diane Coffey, a PhD candidate at the Office of Population Research at Princeton University, compared state domestic products between 1970 and 1983 with the heights of adults born between those years. She found that the state domestic product at the birth year was a robust predictor of adult height. Yet some States are outliers; some north-western States like Jammu and Kashmir and Rajasthan had taller adults than the States’ incomes would have predicted, while some north-eastern States had shorter-than-expected people. So does genetics explain these outliers?

“I have seen no clear and convincing evidence of genetic differences in height potential, either across populations within India, or across populations in different places in the world. Indeed, all of the evidence that I have seen points to the idea that populations with early life environments and care grow to similar heights,” Ms. Coffey told The Hindu. As for the outliers, “height is in large part determined by net nutrition between conception and age two, and net nutrition is a combination of disease and diet quality and quantity. Just because a society has more state net domestic product does not mean that it has a better disease environment or better maternal and infant care practices — the things that really matter for height. That is why it is not surprising that there is not a perfect match between average heights and average income,” Ms. Coffey said.

Most economists agree with her. “My personal belief is that genetics are not important, even between countries, and certainly not between Indian states,” Princeton economist Angus Deaton, one of the world’s foremost authorities on cross-country differences in nutrition, said in an email to The Hindu. One of the few dissenting voices on genetics and malnutrition has been that of Columbia professor and economist Arvind Panagariya who has argued that genetic differences matter in explaining India’s malnutrition numbers (height and weight), which are far higher than those of poorer countries.

K. Thangaraj, president of the Indian Society of Human Genetics, and Principal Scientist at the Hyderabad-based Centre for Cellular and Molecular Biology, told The Hindu that genetic differences could have an impact on variations in height between different population groups within India, but that there had been no research yet that had proved this.

While most economists, including Nobel laureate Amartya Sen, tended to focus on the impact of food consumption on stunting, recent work like that of Mr. Spears has suggested that the lack of sanitation, and more specifically the prevalence of open defecation, can also explain a significant part of the variation in height.

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Printable version | Feb 23, 2020 12:23:35 PM | https://www.thehindu.com/news/national/does-genetics-explain-height-differences-among-indians/article5045718.ece

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