Tall Dutch men appear to be driving people in the Netherlands to get even taller due to natural selection, researchers have found.
Over the past 200 years, people in the Netherlands have gone from being some of the shortest on the planet to the tallest population on Earth.
The increase, of about 20cm (7.8in), over such a short period would appear to be down to environmental factors, but because it is more pronounced than people living in other Western countries, researchers believe there may be something else at play.
Gert Stulp, from the London School of Hygiene and Tropical Medicine, said he and his team were interested in seeing if biological factors or natural selection was also favouring increased heights, making people grow even more.
The study, published in the Proceedings of the Royal Society B: Biological Sciences, showed taller men tend to have more children than their shorter counterparts.
Researchers used data on about 40,000 people spanning three decades and findings consistently showed height related to reproductive output, despite a later age at first birth for taller people.
Among women, those of an average height – not shorter or taller – had highest fertility, meaning tall men appear to be pushing up the height of the population. "Because of the effect on men was a bit stronger than on women, we might conclude selection is favouring taller heights in Netherlands," he told IBTimes UK.
Stulp said previous research looking at height in Western populations has shown a preference for shorter women, with this group tending to have higher fertility than average height or tall women – this is seen in US populations, for example. The apparent preference for average height Dutch women could therefore be working on conjunction with environmental factors, causing increased height.
"It appears that, in the United States, natural selection is working against environmental factors to actively favour shorter stature," the authors wrote. "It therefore becomes relevant to ask whether natural selection has also exerted an influence on stature among the Dutch, and whether selection pressures differ to those in the United States."
Dutch growth spurt may slow down
But will the Dutch keep growing forever? Probably not, Stulp said, noting there is "very likely" a constraint on growth because of the negative health effects eventually seen on tall individuals.
"There are all these examples of excessively tall individuals not having a very long lifespan. Yet there's also something physiologically a bit off with these people for example too many growth hormone factors, so it's difficult to make any conclusions from that, but it seems to be the very tall heights do become detrimental," he said.
However, he also pointed out some Neanderthal skeletons appear to reach heights far greater than currently reached – possibly indicative that the Dutch could grow a little more. He said: "We tend to compare ourselves to our historical counterparts in written history – 200 years ago when we were much shorter.
"But if we look at Palaeolithic records – millions of years ago – we do find fossils that reach heights of 190cm and that is much taller than many of the individuals in populations now. That suggests that many populations haven't reached their evolutionary peak height... but it is difficult to say."
He said a small-scale study due to be published suggests growth in the Netherlands is now levelling off in the same way it has in other Western countries. However, it is not yet clear if this is the case. Next, Stulp and his team plan to use genetic data to conclude if natural selection has been driving the growth of the tallest nation on Earth.