Comment by ackfoobar

> the area under the male height curve that is not under the female one.

It's not obvious to me. Yes the height of the male graph is lower, but is spread wider.

> It’s just the sum of the excess number of men of a given height over and above the number of women of the same height.

It's simply that the female histogram covers part of the male histogram. It's a bit confusing. If I make the graph I will colour the overlapped parts a different colour.

This is not a problem when we show only the bell curves.