Dawkins introduced selection on the individual level in The Selfish Gene (great book, before he became all ranty and weird). This has pretty much killed group selection, but EO Wilson is still clinging on. I think his latest book was a bit too much cherry-picking in defense of group selection for some people.

A few years back Steven Pinker wrote a thing about the "false allure" of group selection based on muddy definitions: http://edge.org/conversation/steven_pinker-the-false-allure-...

Jerry Coyne summarised the debate in NYRB: http://www.nytimes.com/2011/09/11/books/review/the-neighborh...