Answer: So they can see over the Dikes!

If you know the answer to the first question:

"Who are the tallest people in the world?

Then you will know what the second question is (Why?).

Consider: the average height of a Dutch man is (now) about 6'1", the Dutch have been growing.

The answer to WHY? is complex, but apparently more of height is determined by nutrition and lifestyle, and less by genetics, than you think. You can be assured I am renewing my efforts to get nutrition into my two boys: they'll be taking calcium and vitamin tabs every meal... with their McDonalds. [Note to self, check Holland out in terms of McDonalds revenue per capita...]

Additional notes to self: Nutrition, exercise, nutrition, nutrition!