Height is determined by a combination of your genetics and your environment. Factors such as childhood nutrition and disease play an important role in how tall a person becomes. Notably, a study in the British Medical Journal found that the correlation between parent and child height is only 0.5, which means there are myriad factors that determine height.

Height differences in North and South Korea provide a good example of the effects of one’s environment on height. North Korea and South Korea are among the most racially homogeneous countries on earth as ethnic Koreans make up 96% of South Korea’s population and over 99% of North Korea’s population. Thus, based on genetics alone, height among these two countries’ populations should be about the same. But South Koreans are taller. A 2009 study found that South Korean children were about 3 inches taller than their North Korean counterparts and the height of the average South Korean woman is approaching the height of the average North Korean man.

Why the difference? Experts attribute the height difference between the two countries mainly to childhood nutrition. Martin Bloem, head of nutrition at the World Food Programme says poor diet in the early years of life leads to stunted growth. “Food and what happens in the first two years of life is actually critical for people’s height later.” Tragically, many North Korean children are malnourished and thus end up shorter than South Koreans on average.

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