Group Selection - Altruism born from warring, genocidal tribes

Article in The Economist June 6th 2009, p. 77. Taking about research of Samuel Bowles (in Science) "Did Warfare Among Ancestral Hunter-Gatherers Affect the Evolution of Human Social Behaviors?"

Science 5 June 2009: Vol. 324. no. 5932, pp. 1293 - 1298 DOI: 10.1126/science.1168112

(Also work by Mark Thomas "Late Pleistocene Demography and the Appearance of Modern Human Behavior", summarized by NPR "Larger Populations Triggered Stone Age Learning". About population density needed to support technologies, and how population fluctuations caused technologies to be lost, only to be independently discovered later, again and again.)

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Group selection takes place by warring, genocidal tribes (a process described as "genetically terminal" for the losers). This group selection was found to be mathematically compatible with a hard "selfish gene" approach to natural selection. With this approach, there is selection for altruistic traits. Is this the basis for all actual group selection? The more I read, the more I see that a hard "selfish gene" is the correct way to approach natural selection. Is this mechanism of warring, genocidal tribes all we have to make actual group selection?