seems to follow the average temperature in Europe during that time. Higher in the middle ages than now, lowest during the little ice age and ascending since. Obviously better crop yield.

I wonder if there might also be a direct effect via sunlight. Perhaps Americans aren't growing because we are spending too much time indoors as children?

Another possibility is outbreeding. Americans were outbred before Europeans because Americans came from so many places. But Europeans are mating with people who are at greater physical distances and hence greater genetic distances. This may be causing a hybrid effect that is producing greater heights.

Yet another possibility could be ratios of micronutrients. Perhaps the ratio of manganese to zinc or the ratio of omega 3 to omega 6 fatty acids has changed in both populations but in different directions and that is causing a difference in heights.

Yet another possibility is with vaccines. Are Americans now less likely to be vaccinated? Childhood diseases could be stunting growth.

There are a lot of biological possibilities. What ever the cause it it must be happening via some biological mechanism.

Immigration?

It's just the camera angle:

Why do we think they're all tall? Partly because we're used to seeing them 30 feet high on a screen, partly because we think of them as idealized images of what men should be, partly because we think they're more important than we are so we impart height to them in our minds, but mostly because the camera always shoots them from the ground up.

Some interesting height links here.

http://dissectleft.blogspot.com/2004_04_18_dissectleft_archive.html#108223014914281957

THE "SHORT AMERICAN" NONSENSE

I am rather surprised that the story about some Europeans being taller than Americans has attracted such a lot of attention without anyone (as far as I can see) tumbling to what the finding really shows. Even the careful Iain Murray missed it. The finding, in brief, was that the average American height has stopped increasing but average heights in some European countries have not. And some Europeans -- such as the Dutch -- are much taller than Americans on average. The data underlying the finding may not be all that sound but let us assume that they are:

Anti-American commentators have linked the finding to nutrition -- saying that it shows Americans to be poorly nourished. Given the "obesity epidemic" in America, that is a pretty hilarious explanation but it does contain the grain of truth that there is some connection between nutrition and height. As the geneticists (such as Eaves et al., 1999) have shown, final height is a product of genetic potential plus environmental influences -- and nutrition is undoubtedly one of those environmental influences. Putting it another way, your full genetic potential is realized only when the environmental conditions are ideal. So what the data really show is that ONLY IN AMERICA have the ideal environmental conditions for height maximization been realized. That is why Americans have stopped growing. America ALREADY has gained all it can from nutrition etc. The fact that European heights are still growing shows, then, that they still do not have ideal conditions there for realizing their maximum height. They are still catching up. In short, the data show exactly the opposite to what has been claimed: It is Europeans who are lacking in something that influences height. The traditional European habit of consuming fruit and vegetables in preserved and pickled form rather than in fresh form may be the nutritional factor involved.

An immediate objection to my account is of course the fact that SOME Europeans are much taller than Americans on average. How can they be so tall if they have bad nutrition (or whatever else has been holding them back)? Once again the answer is to be found in the Eaves et al (1999) study: The MAIN influence on height is genetics so if coastal North Western Europeans (such as the Dutch and the Scandinavians) have good genetics for height they will still be taller on average even if their nutrition is not ideal. And that coastal North-Western Europeans tend to be very tall has been known at least since the Viking age. Why they have long been among the world's tallest people (along with some very dubiously nourished East Africans) nobody knows for sure but only a small percentage of the American population is of coastal North Western European ancestry so the final American average must be much lower. And the fact that the legionaries of the ancient Roman empire were real shorties suggests that average national height is a very minor factor (if it is a factor at all) in national achievement and felicity.

Reference
Eaves, L.J., Martin, N.G., Meyer, J.M. & Corey, L.A. (1999) "Biological and cultural inheritance of stature and attitudes". In: Cloninger, C.R., Personality and psychopathology. Washington, D.C.: American Psychiatric Press.

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