Confirmation for Dunbar's theory of gossip?

Robin Dunbar's theory of language and gossip developed in here and in his books "Grooming, Gossip and evolution of language" and "The Human Story" (See also the Wikipedia article on Dunbar's number)seems to get some more confirmation in recent research according to "Facts Prove No Match for Gossip, It Seems":
"The donor was told that the source of the gossip didn’t have any extra information beyond what the donor could already see for himself. Yet the gossip, whether positive or negative, still had a big influence on the donors’ decisions, and it didn’t even matter if the source of the gossip had a good reputation himself. On average, cooperation increased by about 20 percent if the gossip was good, and fell by 20 percent if the gossip was negative." (via 3quarksdaily)