Martin Enserink in Science:
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. Just how these peoples became so tall isn't clear, however. Genetics has an important effect on body height: Scientists have found at least 180 genes that influence how tall you become. Each one has only a small effect, but together, they may explain up to 80% of the variation in height within a population. Yet environmental factors play a huge role as well. The children of Japanese immigrants to Hawaii, for instance, grew much taller than their parents. Scientists assume that a diet rich in milk and meat played a major role.
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.