I wouldn't waste your brain cells and energy worrying about this, folks. Seventy-one percent of the Earth is covered in water, to start with. Now think of all the "empty" space - agricultural fields, deserts, high mountain ranges - where no one lives. Ever driven any distance across the US for example, or flown anywhere and looked out the window? Flying to Beijing, for example, even after we had crossed the Pacific ocean, we spent what seemed like hours and hours flying over empty Siberian tundra.

Here's a good "population denisty map" from NASA.



You can download a much bigger version here: http://visibleearth.nasa.gov/view_rec.php?id=116

but look at how much of even the land areas are sparsely populated.

I'm not going to lose any sleep over this. And I live in one of the dark red areas!