Lecture on Altruistic Behavior, Group Selection, and Kin Selection

Introduction to Altruistic Behavior

• Altruistic behavior benefits the group or species but decreases individual fitness.
• Example: Diving into the ocean to reduce overpopulation of lemmings.
• Despite group benefits, altruistic alleles should decrease in frequency because they reduce individual fitness.

Selfish vs. Altruistic Alleles

• Populations have both selfish (red) and altruistic (blue) alleles.
• Selfish individuals prioritize their own survival and reproduce more successfully.
• Over time, selfish alleles tend to become fixed in the population.

Group Selection Theory

• Group Selection: Populations with altruistic alleles might survive better (e.g., warning calls to avoid predators).
• Populations with selfish alleles are more likely to go extinct.
• However, group selection is less effective than individual selection because:
  • Individuals reproduce and die quicker than populations go extinct.
  • Gene flow allows selfish alleles to migrate into altruistic populations, gaining benefits without costs.

Criticism of Group Selection

• Williams’ criticism highlights that individual selection dominates over group selection.
• Selfish alleles spread faster within populations than altruistic alleles can stabilize within a group.

Kin Selection as an Explanation

• Kin Selection focuses on inclusive fitness, which includes the individual's own fitness and the fitness of close relatives.
• Close relatives share alleles due to common descent, increasing the probability of allele transmission if relatives reproduce successfully.

Hamilton's Rule

• Explains how altruistic traits can increase in frequency:
• Hamilton's Rule: Altruism increases if ( rb > c )
  • ( r ) = degree of relationship.
  • ( b ) = benefit to relatives.
  • ( c ) = cost to the altruist.
• Example: Sacrificing oneself for two siblings or eight cousins (J.B.S. Haldane's story).

Degree of Relationship

• ( r = \frac{1}{2} ) for parents/offspring or full siblings.
• ( r = \frac{1}{4} ) for half-siblings, grandparents/grandchildren, uncles/nephews, or double first cousins.
• ( r = \frac{1}{8} ) for first cousins.

Conclusion

• Natural selection acts on individuals, leading to changes in allele frequencies.
• Inclusive fitness/kin selection offers a broader understanding by considering shared alleles within family units.
• Evolution is about allele frequency changes due to individual fitness differences, not whole populations being universally more fit.