All this talk about empathy made me remember this website:
http://www.pointlesswasteoftime.com/monkeysphere.html
The basic premis is that you can really only truly care about a limited number of people (those within your sphere) and the closer in your sphere that they are located, the more empathy/caring you have with/for them. It's an amusing read and has a link to a research article where the pull out the people have a sphere of about 150 other people.