The evolution of group selection

Group selection enthusiasts were dissatisfied with the consensus that group selection couldn't compete with individual-level selection. They counter-attacked in a number of ways, saying that:

• The insistence by critics on groups being disjoint was mistaken - groups could still be targets of selection even if they overlapped.

• Kin selection was actually a type of group selection - acting on family groups.
• Reciprocal altruism was actually a type of group selection - involving small groups of reciprocators.
• Some major evolutionary transitions showed group selection in action - today's organisms were once yesterday's groups.
• Group selection had firm mathematical foundations - in the form of the Price equation.
• Laboratory experiments on group selection showed that it was potentially a powerful force.

• There are circumstances where between-group migration was very low - for example with parasites and symbiotes that spent most of their time inside other organisms.

• Group selection explained altruism, religion, senescence, sexual recombination - etc.

They also pointed out that a number of criticisms that had been leveled at group selection were wrong:

• The idea that between-group variation would be destroyed by migration and/or within-group selection was wrong - since substantial between group variation could be observed empirically - for example in a species such as our own.

• The idea that groups are not replicators - and so aren't a valid "level of selection" - was bunk.
• The widespread 50:50 sex ratio was not an argument against group selection for that trait - group selection could easily favour a 50:50 sex ratio.

A number of these points seemed quite reasonable - however...