Gardner A (2015) Group selection versus group adaptation. Nature 524, E3-E4.
Pruitt and Goodnight 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. They experimentally manipulate this ratio to show that it influences a colony’s reproductive success. Pruitt and Goodnight conclude that this work demonstrates group-level adaptation and contradicts an earlier theoretical analysis. Here, I show that this conclusion is unfounded and arises from a conceptual misunderstanding.