Debate centers on which groups, how often, and why. As a result, the paper fails in its attempt to establish sophisticated group selection as an important part of the reigning biological paradigm.
Humans display many behaviors that appear difficult to explain in individual selection terms.
The Hutterite example given is particularly instructive, as they are cognitively manipulating migration rates by identifying and expelling non-cooperators. If rook flocks were closed and individuals collectively attacked pairs laying large clutches, Wynne-Edwards would have carried the day. For chimpanzees, they further argue that the ability of a party to physically immobilize a lone opponent lowers the cost of aggression still more. Now imagine such an attack by a group of hominids carrying stone weapons. The impact, as it were, of such tools cannot be overemphasized.