"The general form of Hamilton’s rule makes no predictions and cannot be tested empirically"
It's the old claim that "survival of the fittest" is a tautology (since the fittest are those that survive) repackaged for kin selection.
Evolutionary biologists have long had a stock answer to the claim that "survival of the fittest" is a tautology. This hinges on the difference between expected fitness and observed fitness.
"Survival of those with the highest observed fittesses" would indeed be a kind of circular argument. However, "survival of those with the highest expected fittesses" is making a falsifiable statement about the model with which the expected fitnesses are calculated.
Nowak and Wilson say:
The mathematical investigation of HRG reveals three astonishing facts. First, HRG is logically incapable of making any prediction about any situation because the benefit, BB, and the cost, CC, cannot be known in advance. They depend on the data that are to be predicted. At the outset of an experiment, BB and CC are unknown, and so there is no way to say what Hamilton’s rule would predict.
Those are observed fitnesses (measured after the fact). Rather obviously, if you want to make predictions, you need to be using expected fitnesses when determining B and C. Nowak and Wilson are simply mistaken in claiming that there's no way in which these could possibly be calculated in advance. You could predict these values by using a mathematical model of the situation, or by using a computer simulation - for example.
IMHO, it is pretty amazing that some scientists bothered to write a whole paper about this issue, without first understanding it.
