What Is Altruism in Evolutionary Biology?

• Altruistic behavior is defined as any action that increases another individual’s fitness while decreasing the actor’s own fitness.

• The evolutionary explanation for why such behaviors evolve is rooted in the concept of indirect fitness—the idea that helping relatives can increase the propagation of shared genes, even if it reduces the helper’s own direct reproductive success.

• Hamilton’s Rule formalizes this: altruism is favored when $rb-c>0$, where $r$ is genetic relatedness, $b$ is the fitness benefit to the recipient, and $c$ is the fitness cost to the altruist.

Correct and Incorrect Statements About Altruism

Let’s examine the given statements:

1. “It is the net gain of direct fitness when sociality is facultative.”
   This statement is incorrect.

   • Altruism, by definition, involves a loss of direct fitness for the actor, not a net gain.

   • In facultative altruism, the loss of direct fitness is temporary and may be compensated by future direct reproduction, but the key point is that the act itself reduces direct fitness in favor of indirect fitness.

   • The evolutionary benefit of altruism comes from indirect fitness gains (helping relatives), not direct fitness.

2. “It is under positive selection via indirect fitness benefits that exceed direct fitness costs.”
   This is correct and aligns with Hamilton’s Rule.

3. “It generates indirect benefit by enhancing survivorship of kin.”
   This is correct and describes the mechanism of kin selection.

4. “It is favoured when rb – c > 0 where c is fitness cost to altruist, b is fitness benefit to recipient; and r is genetic relatedness.”
   This is correct and is the formal mathematical expression for when altruism is favored by natural selection.

Conclusion

The incorrect statement about altruism is:

(1) It is the net gain of direct fitness when sociality is facultative.

Altruism is not about gaining direct fitness, but about sacrificing it for the indirect fitness benefits gained by helping relatives. This distinction is fundamental to understanding how altruistic behaviors evolve in the animal kingdom.