Can we predict the future height of a newborn baby? On one hand, if both parents are short, the chances of becoming a basketball player are not high. On the other hand, factors such as nutrition and childhood illnesses also play a role.
Height is a complex trait that is affected by both genetic and environmental factors, and the question is which is more important – heredity or environment?
One way to answer this question is through twin studies, in which identical twins that share the same genetic makeup are followed and differences in their height are examined. The results are compared to height differences among the general population.
However, in addition to their genetic makeup, twins also usually share a common environment, which complicates the analysis. Therefore, the differences in height between identical twins are compared to the differences between fraternal twins – who also share a similar living environment but share only half of their genetic makeup, similar to non-twin siblings.
This approach allows us to estimate the percentage of difference in height explained by genetic factors and those explained by environmental factors.
So, is the claim “if you don’t eat, you won’t grow” actually correct?
It turns out that this is only partially true. Various studies estimate that the heritability of height is about 80% – in other words, the vast majority of the variation in height that we see around us comes from our DNA, and only about one-fifth of this variation is due to the environment.
In addition, it seems that the environment has a greater effect on women than on men – for men, heritability is closer to 90%, while for women it ranges between 70% and 80%. So, if anything, it's more accurate to direct the statement "if you don't eat, you won't grow" toward girls.
Constant influence of the environment
Historically, the influence of the environment on people’s height was considered to be smaller in wealthier societies. When even the lower classes have no shortage of basic nutrients, and when there are vaccines and medical treatments for many childhood diseases, each person should reach the maximum potential height determined by their genes.
However, a relatively recent large-scale study, based on data collected over more than a century and including over 140,000 sets of twin from 20 different countries, concluded that although this assumption sounds logical it is probably incorrect.
The study was conducted on sets of twins born since 1886 and examined the influence of the environment and heredity on height variation among the study participants over the years. The researchers found that throughout the 20th century, as living standards rose, average height consistently increased, indicating an influence of the environment on height.
In 1886 the average height of a European woman was about 160 cm, while in 1994 it was about 166 cm. The heights of men and women in Europe, Australia and East Asia increased at a similar rate. The conclusion is that a rise in living standards, including better nutrition and better health services, leads to an increase in height.
Nonetheless, the heritability of height, to the extent the variation is influenced by genetics, was almost unchanged over the century and remained at about 80%. In other words, one would expect that in today’s Western society, where most people have access to basic food and vaccines, all height variation should be due to genetic differences.
However, the study found that this is not the case – even today, about one-fifth of the variation in height in the population is due to differences in environmental conditions.
What are the environmental conditions that influence our height today, if they are not childhood diseases or lack of some nutrient? The aforementioned study did not specifically address this question, but if you want to increase the influence of the environment on your height, the most effective method is simply to have been born a woman.
Content distributed by the Davidson Institute of Science Education.