[jpeloquin]

Right, "sharing" here must mean DNA that was cloned from the same ancestral DNA strand, not merely that it shares the same informational content. I got lost in the analogies that frame things in terms of what's "better" for the organism and lost sight of this.

The most important thing from the perspective of replication of a DNA strand is the number of copies of DNA passed to the next generation, and future generations, right? Which would be 0.75 * (mean marginal increase in next-generation sisters) + 0.5 * (mean # offspring). The probability that these next-generation individuals actually get to reproduce in turn would also factor in somewhere.

What's also interesting is that if we take the point of view of the queen (through whom the altruistic genes must pass), the queen's reproductive strategy is relatively few children + hordes of sterile helpers + killing her own sisters. So are we talking about a fitness advantage of altruistic traits (maximizing # sisters), or a fitness advantage from selfish traits [maximizing P(fertile child survival) I guess, since # children is small] that produce hordes of sterile helpers?

Edit: Circling back to the organism perspective, in the sense of "I would gladly give up my life for two brothers or eight cousins.", how many bees is it worth giving up one's own life for in that specific sense? We do have a common ancestor after all and thus a non-zero R-factor.