I think what rcthompson was asking is why can't both kin altruism and group altruism exist as primary causes? If there's a genetic (as opposed to memetic) basis

I think what rcthompson was asking is why can't both kin altruism and group altruism exist as primary causes? If there's a genetic (as opposed to memetic) basis, it's conceivable* that there is a single gene that, if mutated, would cause individuals to care about the group, but not direct kin any more than the group at large, or to care about close kin, but not the larger group. Given how much of biology is layers of overlapping, cooperative systems, I would guess this is the most likely idea: that both kin selection and group selection are active, to varying degrees in different populations. * Though unlikely