A new study from the Netherlands suggests evolution is helping make Dutch people taller.
Gert Stulp stands 6 feet, 7 inches tall. His height makes him especially self-conscious at scientific conferences when he rises to describe his research as a demographer at the London School of Hygiene & Tropical Medicine. “It’s always quite embarrassing,” he said.
Stulp, who is Dutch, studies why his fellow citizens are so tall.
Today, the Dutch are on average the tallest people on the planet. Just 150 years ago, they were relatively short. In 1860, the average Dutch soldier in the Netherlands was 5-foot-5. American men were 2.7 inches taller.
Since 1860, average heights have increased in many parts of the world, but no people have shot up like the Dutch. The average Dutchman now stands more than 6 feet tall. And while the growth spurt in the United States has stopped in recent years, the Dutch continue to get taller.
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For years, scientists have sought to understand why average height has increased, and why the Dutch in particular have grown so quickly. Among other factors, the Dutch have a better diet than in the past, and they have better medical care. But Stulp and his colleagues have found evidence suggesting evolution is also helping to make the Dutch taller.
The new study, published Tuesday in Proceedings of the Royal Society B: Biological Sciences, was made possible thanks to a medical database recently established in the Netherlands called LifeLines. The database contains a vast amount of information, including genetic profiles and medical records, about tens of thousands of Dutch families.
Stulp and colleagues analyzed data on 42,612 men and women older than 45, looking at the height of their subjects and how many children they had. Dutch men who were taller than average had more children than those of average or lower than average height, the researchers found.
Among those born in the early 1950s, for example, men who were 5 feet, 6 inches had on average 2.15 children. Men who were 6 feet, 1 inch had 2.39 children. The scientists found that the trend toward taller men having more children persisted for more than 35 years.
Among women, the pattern was more complex. Overall, Dutch women of average height had the most children. But that was because taller women tended to take longer to become mothers. Once they entered their childbearing years, taller mothers had children at a faster rate than shorter women.
“I was not expecting to find these patterns,” Stulp said. “The Dutch really seem to be different.”
It is possible that an environmental factor caused some Dutch people both to grow tall and to have more children, Stulp said. Wealthier Dutch people could end up taller and with more children, for example.
But when Stulp and his colleagues controlled for how rich their subjects were, the link between height and children persisted. It also remained when they tried factoring out other variables, such as education.
Stulp therefore suspects genes are involved. Under identical conditions, some people will grow taller than others because they carry certain genetic variations.
He and his colleagues are gathering more data, and he hopes to determine how much of increase in height is a result of natural selection.