The Dutch win the award for the world’s tallest people, with the average man standing 6 feet tall and the average woman coming in at 5-foot-7. Records show that the Dutch are continuing to grow, and a recent study has set out to answer the all-important question of why.

Although proper nutrition offers insight into why the Dutch are the world’s tallest people, a healthy diet only provides a partial explanation for their height. For example, the Dutch and Americans have similar high-calorie diets rich in meat and dairy. While the average American man has grown 2.4 inches in the last 150 years, Dutch men have grown an impressive 8 inches in the same timeframe, The Guardian reported. Gert Stulp, a specialist in population health at the London School of Hygiene and Tropical Medicine, set out to find what other factors play a role.

Stulp and his team looked through LifeLines, a Dutch “Biobank” containing details of the lives and health of more than 94,500 people who lived in the northern Netherlands from 1935 to 1967. In their record-searching, a trend began to emerge. It seemed that the taller the individuals, the more children they were likely to have. Seeing as height is a highly heritable trait, this practice caused the tall gene to not only survive but also enhance.

“Because taller individuals would have more offspring in the next generation who would be taller, the average height in that generation would be a bit taller on average than the preceding generation, if all else is equal,” explained Stulp, as reported by The Guardian.

According to the records, men who were nearly 3 inches over the national average tended to have more offspring than men who were shorter than the average height. The same proved true for Dutch women, whose fertility also increased with their height. When tall men breed with tall women they tend to have more children than other height match-ups.

What makes the height of the Dutch so unique is that this success of height is not seen in other cultures. For example, records show that in the United States the combination of average-sized men paired up with short women yielded the most offspring, Science Magazine reported.

It’s likely that both environmental factors and natural selection combined to give the Dutch their famous height. Interestingly, the researchers hypothesize that, like all things in life, natural selection’s inclination toward height may not last forever. If this trend follows the same pattern as previous trends in sexual reproduction, it will favor one trait for a number of generations followed by a period of either stabilization or a return to the opposite trend. Still, for now, the Netherlands remains the tallest country in the world.

Source: Stulp G, Barrett L, Tropf FC, Mills M. Does natural selection favour taller stature among the tallest people on earth? Proceedings B. 2015.