Inclusive fitness

The theory of inclusive fitness argues that a gene for altruistic behavior will increase in a population when the reward for the altruism, proportional to the degree of relatedness of a recipient, is greater than the cost to oneself.  The problem with this is that traditional methods of measuring relatedness would say that each parent, offspring and sibling all have an r-value of 0.5.  That is, there is a 50% chance that any given gene that you share is via common ancestry.  That is, it is equally advantageous to help a parent, a sibling or offspring.  However, in terms of human examples, I think that a parent would be willing to make a sacrifice for their child more readily than for their sibling or parent.  Altruism toward individuals with an r value of 0.5 is common in females of a social species.  In many cases, there is help between sisters or mothers and daughters or even aunt and niece, but I'm fairly confident that it is much more common to see males only their parent, or less commonly their sibling or offspring.  I think that the reason for this is that the male is geared for more of what will be the next generation result of his help.  A parent can produce another sibling so that the inclusive fitness is increased by another individual of r=0.5, whereas helping a sibling or offspring produces individuals of r=0.25.  Therefore, I would expect that you would see male helpers of their parents at a certain rate in monogamous species, and about half as commonly for a parent in non-monogamous species and for either siblings or offspring.