You’re assuming that the benefits of an adaptation can only be linear in the fraction of group members with that adaptation. If the benefits are nonlinear, then they can’t be modeled by individual selection, or by kin selection, or by the Haystack model, or by the Harpending & Rogers model, in all of which the total group benefit is a linear sum of the individual benefits.
For instance, the benefits of the Greek phalanx are tremendous if 100% of Greek soldiers will hold the line, but negligible if only 99% of them do. We can guess—though I don’t know if it’s been verified—that slime mold aggregative reproduction can be maintained against invasion only because a slime mold aggregation in which 100% of the single-cell organisms play “fairly” in deciding which of them get to produce germ cells survives, while a slime mold aggregation in which just one cell’s genome insisted on becoming the germ cell would die off in 2 generations. I think individual selection would predict the population would be taken over by that anti-social behavior.
You’re assuming that the benefits of an adaptation can only be linear in the fraction of group members with that adaptation. If the benefits are nonlinear, then they can’t be modeled by individual selection, or by kin selection, or by the Haystack model, or by the Harpending & Rogers model, in all of which the total group benefit is a linear sum of the individual benefits.
For instance, the benefits of the Greek phalanx are tremendous if 100% of Greek soldiers will hold the line, but negligible if only 99% of them do. We can guess—though I don’t know if it’s been verified—that slime mold aggregative reproduction can be maintained against invasion only because a slime mold aggregation in which 100% of the single-cell organisms play “fairly” in deciding which of them get to produce germ cells survives, while a slime mold aggregation in which just one cell’s genome insisted on becoming the germ cell would die off in 2 generations. I think individual selection would predict the population would be taken over by that anti-social behavior.