Group selection versus group adaptation

Pruitt & Goodnight (hereafter “PG”) describe how the ratio of aggressive versus docile females varies among naturally-occurring colonies of the social spider Anelosimus studiosus – with larger colonies exhibiting more aggression in high-resource environments and the reverse in low-resource environments – and they experimentally manipulate this ratio to show that it influences a colony’s reproductive success. PG conclude that this work demonstrates group-level adaptation and contradicts an earlier theoretical analysis. Here, I show that this conclusion is unfounded and owes to conceptual misunderstanding.