Dr Gert Stulp, London School School of Hygiene and Tropical Medicine
The Dutch are the tallest nation in the world and, on average, they've grown a staggering 20 centimetres in less than 200 years. Height is determined by a complex interaction of our genes and our environment, but the driving force enabling the Dutch to reach their current lofty height may be down to a higher rate of reproduction among taller men, according to a new study from Gert Stulp from the London School School of Hygiene and Tropical Medicine. Kat Arney got the long and the short of it...
Gert - So, we got our hands on a very large dataset from the north of the Netherlands and the northeast, the tallest part of the Netherlands. And we basically examined whether height, if we control for factors like education and income, and health was related to the number of children.
Kat - So, that will tell you if there's some kind of natural selection, some kind of breeding effect going on.
Gert - Yes. If taller individuals would have more children, this might be part of the reason why the Dutch become taller because if taller individuals have more children and we know height is highly heritable, then itís plausible that the next generation consists of children who become taller themselves.
Kat - So, what did you find when you looked at all these data?
Gert - We found that above average height men had higher fertility compared to their shorter counterparts. In women, we found that average height women had more children compared to shorter and taller women. The effect of height was much stronger for men. So, if we combine these two findings for men and women, we can conclude that itís very likely that natural selection would favour taller heights.
Kat - So, thatís kind of the family side of it. But obviously, height isnít just down to our genetics. What do you think may be some of the other factors that are on top of this genetic background? What are some of the other factors that may be increasing height in the Netherlands?
Gert - In the Netherlands, it has been suggested that our higher rates of consumption of milk and cheese have increased our heights and also, our good healthcare system and good access to healthcare, and very importantly, low levels of inequality in our society has also been attributed to our height advantage.
Kat - So, the Netherlands is very equal society. There's not that much difference between the richest and the poorest.
Gert - Yes. Less so than many other countries.
Kat - It seems very strange that something like inequality might be playing a role in height. How could that be?
Gert - Well, the reason is that if you are stressed for resources, either in nutrition or maybe when you have a higher risk of diseases, your body has to fight off these diseases or have to cope with the stress. That often comes at the cost of growth. So, we see sort of in poorer areas of society, that growth is stunted. So, children do not reach their full growth. Inequality have such an effect on height because if you have very unequal societies, this means that there will be a very large part of the population that is really stunted in their growth. Whereas in sort of more equal societies, you find itís less.
Kat - Do you think this could explain why some other countries that are very maybe similar to the Netherlands in terms of their diet, their environment, haven't attained this kind of astronomical height that the Dutch have?
Gert - I think that would be a very plausible explanation. Definitely, between the United States and the Netherlands, that would seem a factor. Interestingly, it has been argued that 150 years ago, the Dutch were almost as short as a European nation and at that time, the Netherlands was also much more unequal. Ironically, the Americans were the tallest western nation at that time and at that time, America was almost a much more equal than it is now.
Kat - You are an extremely tall man. You're well over at 6 foot tall and towering above me. I'm extremely small. So, when I go to for example, medieval places, they're kind of built for my sort of height. Have humans always got taller?
Gert - Indeed. If you look at historical times, we have become much, much taller and we think, how much taller can we get? But itís perhaps very interesting to also look a little bit further into evolutionary time because there are fossils found, from hundreds of thousands of years ago that actually were estimated to have heights of about 190 centimetres which is much taller than you and also many others living in western countries. So, it might very well be that our evolutionary heritage allows us for even more growth. Having said that, there is some evidence that the Dutch have stopped increasing in recent times which might suggest some biological limits to growth. That said, we also live in time of relative financial recession and it could very well be that when the environmental quality improves again, when things are looking up again, that the Dutch might even grow further and further, until a point that they're perhaps gravity will severely constrain further growth.
Georgia - A tall story indeed. That was Gert Stulp from the London School of Hygiene and Tropical Medicine.