Increase in size is not evidence of evolution.
It merely means that the local conditions have changed, and that the current generation has adapted to them. In Japan's case, a large increase in the consumption of animal protein and dairy products.

It works the other way: the population of Argyll, Sutherland and the Western Highlands were the tallest people in Europe on average in 1900. The ones who migrated to Glasgow lost up to 8 inches in average height, due to poor nutrition. Yet their cousins, many of whom lived less than 40 miles remained tall.
(all my scars face forward possesses 2.5% of a hyperalloy combat chassis, Tue 6 Apr 2010, 18:21, Reply)