The evolution of altruism?

I'm rereading this fascinating book called Unto Others: The Evolution and Psychology of Altruism. One of its authors, Elliott Sober, was the professor of my Philosophy 101 class I took at University of Wisconsin-Madison.

The complexity of the debate makes it impossible to go into detail here, but the general premise is that the field of evolutionary biology mistakenly dismissed the possibility of altruism's evolution by means of group level selection. According to Sober and Wilson, evolution not only selects the fittest traits at the level of the gene and individual organism, but at the group level as well. They argue that altruism could only be favored by group level evolution. Both gene and individual level evolution disfavor altruism and would not allow it to persist in nature.