Although bonobos, orangutans, and Western gorillas have less hostile relationships with neighboring groups than do chimpanzees, none of these species has the tolerance of the dolphins, or their ability to form alliances outside of their immediate community. Among mammals, only elephants come close; though they live in matrilineal groups, elephants maintain relationships outside of these, forming large, stratified societies. But even these large societies are still primarily with close kin, and are not changeable as are the dolphins' alliances.
Because female dolphins give birth to only single calves that are separated by several years, the males cannot count on forming alliances with close kin. Instead, male dolphins must learn how to make and maintain friendships -- demanding social skills that are likely to have contributed to the dolphins' large brains... But it's not just the number of social relationships the dolphins must maintain, he adds. "It's the uncertainty of those third-level alliances. It's those guys you rarely see. What have they been up to since the last time you met them? Are they still on your side?"-- from Meet the Dolphin Mafia. Original paper here. P.S. 'Will we ever...talk to dolphins?'