You seem to be forgetting that even two hundred years ago, the human population was much smaller. Better nutrition explains the population explosion better than anything. Even a hundred years ago, many people in London were malnourished. Interesting to read Charlie Chapalin’s autobiography. He was small because he grew up without much food. The Japanese today are much larger than their great grandparents.
Forsooth. In particular, Japanese girls are much, um, 'larger' than their grandmoms.