Group vs Individual Selection

Group Selection

• Salmon migrate thousands of miles from the open ocean into a small stream where they spawn and die, killing themselves with exhaustion to ensure survival of the species.
• Originally mentioned by Darwin 'Descent of Man'
  
• Wynne-Edwards - Each group or species controls its rate of consumption. E.g. individuals restrict their birth-rate to prevent over-population.
• Only those possessing population-regulating genes survive to reproduce

Does Group Selection occur?

• Williams, Maynard-Smith & Dawkins indicated that most adaptive evolution occurs through individual selection.
  
• Adaptive traits are selected as they benefit the survival/reproduction of indiviudals, not groups. 
• 'Williams Revolution' - Discredited Group Selection

Individual Selection

• Maynard-Smith (1964) - Groups don't go extinct fast eenough for group selection to be an important part of evolution. Go extinct faster.
• If an individual behaves selfishly it will usually pass on more of its genes
• Williams (1966) - Individuals are expected to behave so as to maximise their chances of reproduction.
• Dawkins (1989) - Individuals are expected to behave selfishly

Evolutionary Stable Strategies

• A strategy is not evolutionarily stable if it can be "invaded" by another strategy
• E.g. Group Selection is…