Two methodologies are available for calculating the fitness of altruism, namely inclusive fitness and neighbor modulated fitness. Inspired by the second methodology, Fletcher and Doebeli (2009) propose a new approach to the evolution of altruism, where assortment plays a fundamental role. Weak and reciprocal altruism appear as genuine cases of altruism in this new approach. In this paper I argue that the approach implies a new concept of altruism: a cooperative behavior is altruistic whenever it requires positive assortment between altruists to evolve. Moreover, assortment between altruists is controlled by traits that evolve by natural selection in the individual altruists. The role of assortment, and its being controlled by individual traits that co-evolve with altruistic ones, is the fundamental new insight promoted by the neighbor modulated fitness approach. I also examine and reply to the criticisms of inclusive fitness theorists against this new perspective on altruism.