What Is Hamilton’s Rule?

Hamilton’s rule, formulated by the evolutionary biologist W.D. Hamilton, states that an altruistic gene will spread in a population if the genetic benefit to the recipient, weighted by relatedness, exceeds the cost to the donor. The rule is typically expressed as:

$$rB>C$$

or, rearranged,

r>CBr>BC

Where:

• r is the coefficient of relatedness between the donor and recipient,

• B is the benefit to the recipient,

• C is the cost to the donor.

Why Is This Rule Important?

Hamilton’s rule provides a clear explanation for the evolution of altruism—behaviors that reduce an individual’s own reproductive success while increasing that of others. According to this principle, such behaviors can evolve if they increase the overall genetic representation of the altruist’s genes in the next generation, either through direct offspring or by helping relatives (who share many of the same genes) to reproduce.

Examples in Nature

• Social insects: Worker bees forgo reproduction to help the queen, their close relative, produce more offspring.

• Mammals and birds: Individuals may feed or protect siblings or nieces/nephews, increasing the survival of shared genes.

• Adoption in animals: Some animals adopt orphaned relatives when the genetic benefits outweigh the costs.

Hamilton’s Rule vs. Other Concepts

• Red Queen Hypothesis: Explains evolutionary arms races, not altruism.

• Handicap Principle: Relates to costly signaling in mate choice.

• Competitive Exclusion Principle: Describes competition between species, not social behavior.

Conclusion

The idea that an altruistic gene will be favored if r>CBr>BC is known as Hamilton’s rule. This principle is a cornerstone of modern evolutionary theory, explaining the genetic logic behind cooperation and altruism in the natural world.

Correct answer: (3) Hamilton rule