Did Natural Selection Make the Dutch the Tallest People on the Planet?

Martin Enserink, Science Mag, April 7, 2015

Insecure about your height? You may want to avoid this tiny country by the North Sea, whose population has gained an impressive 20 centimeters in the past 150 years and is now officially the tallest on the planet. Scientists chalk up most of that increase to rising wealth, a rich diet, and good health care, but a new study suggests something else is going on as well: The Dutch growth spurt may be an example of human evolution in action.

The study, published online today in the Proceedings of the Royal Society B, shows that tall Dutch men on average have more children than their shorter counterparts, and that more of their children survive. That suggests genes that help make people tall are becoming more frequent among the Dutch, says behavioral biologist and lead author Gert Stulp of the London School of Hygiene & Tropical Medicine.

“This study drives home the message that the human population is still subject to natural selection,” says Stephen Stearns, an evolutionary biologist at Yale University who wasn’t involved in the study. “It strikes at the core of our understanding of human nature, and how malleable it is.” It also confirms what Stearns knows from personal experience about the population in the northern Netherlands, where the study took place: “Boy, they are tall.”

For many years, the U.S. population was the tallest in the world. In the 18th century, American men were 5 to 8 centimeters taller than those in the Netherlands. Today, Americans are the fattest, but they lost the race for height to northern Europeans–including Danes, Norwegians, Swedes, and Estonians–sometime in the 20th century.

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The Dutch have become so much taller in such a short period that scientists chalk most of it up to their changing environment. As the Netherlands developed, it became one of the world’s largest producers and consumers of cheese and milk. An increasingly egalitarian distribution of wealth and universal access to health care may also have helped.

Still, scientists wonder whether natural selection has played a role as well. For men, being tall is associated with better health, attractiveness to the opposite sex, a better education, and higher income–all of which could lead to more reproductive success, Stulp says.

Yet studies in the United States don’t show this. Stulp’s own research among Wisconsinites born between 1937 and 1940, for instance, showed that average-sized men had more children than shorter and taller men, and shorter women had more children than those of average height. Taken together, Stulp says, this suggests natural selection in the United States pulls in the opposite direction of environmental factors like diet, making people shorter instead of taller. That may explain why the growth in average American height has leveled off.

Stulp–who says his towering 2-meter frame did not influence his research interest–wondered if the same was true in his native country. To find out, he and his colleagues turned to a database tracking key life data for almost 100,000 people in the country’s three northern provinces. The researchers included only people over 45 who were born in the Netherlands to Dutch-born parents. This way, they had a relatively accurate number of total children per subject (most people stop having children after 45) and they also avoided the effects of immigration.

In the remaining sample of 42,616 people, taller men had more children on average, despite the fact that they had their first child at a higher age. The effect was small–an extra 0.24 children at most for taller men–but highly significant. (Taller men also had a smaller chance of remaining childless, and a higher chance of having a partner.)  The same effect wasn’t seen in women, who had the highest reproductive success when they were of average height.  The study suggests this may be because taller women had a smaller chance of finding a mate, while shorter women were at higher risk of losing a child.

Because tall men are likely to pass on the genes that made them tall, the outcome suggests that–in contrast to Americans–the Dutch population is evolving to become taller, Stulp says. {snip}

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