[Humpbacks whales] deliberately interfere with attacking killer whales to help others in distress. They dont just defend their own babies or close relatives. They intervene on behalf of other species - a gray whale calf with its mother, a seal hauled out on an ice floe, even an ocean sunfish. Humpbacks act to improve the welfare of others; the classic definition of altruism. Robert Pitman, a marine ecologist ... describes a pivotal encounter he witnessed in Antarctica in 2009. A group of killer whales washed a Weddell seal they were attacking off an ice floe. A pair of humpbacks ... inserted themselves into the action. One of the huge humpbacks rolled over on its back and the 180-kilogram seal was swept up onto its chest between the whales massive flippers. And when the seal started slipping off, the humpback, according to Pitman, gave the seal a gentle nudge with its flipper, back to the middle of its chest. Moments later, the seal scrambled off and swam to the safety of a nearby ice floe. Pitman started asking people to send him similar accounts. Soon he was poring through observations of 115 encounters between humpbacks and killer whales, recorded over 62 years. So are humpbacks compassionate? When I pose the ... question to Pitman he [responds], When a human protects an imperiled individual of another species, we call it compassion. If a humpback whale does so, we call it instinct. But sometimes the distinction isnt all that clear.