Applying Hamilton’s Rule to Uncle-Nephew Altruism

For an uncle helping a nephew, the genetic relatedness (r) is 0.25. According to Hamilton’s Rule, the condition for an altruistic gene to spread is:

$$0.25\times B>C$$

To find the minimum benefit (B) required for the allele to spread, rearrange the equation:

B>C0.25B>0.25C$$B>4C$$

This means the fitness benefit to the nephew must be four times the cost incurred by the uncle for the altruistic behavior to be favored by natural selection.

Why Four Times the Cost?

• Uncle and nephew share 25% of their genes.

• The benefit to the nephew must be large enough, when discounted by this relatedness, to outweigh the cost to the uncle.

• Only when the benefit is at least four times the cost will the gene for such altruism increase in frequency in the population.

Conclusion

According to Hamilton’s Rule, alleles that cause uncles to care for nephews will spread only if the fitness benefit is four times the cost of care.

Correct answer: (4) four times the cost of care