One of the things that makes us human is an ability to think ahead when we interact with someone and adapt our behavior if we expect to encounter that person again. A tiny tropical fish also seems to have this ability, according to new research, behaving more cooperatively with fish it is likely to encounter more often and taking sneaky bites off those it doesn't.

The researchers said this was the first time non-humans had been shown to exhibit what economists term the "shadow of the future" behavior, in which people's behavior changes depending on whether they are likely to meet again in the future.

The researchers studied cleaner fish in French Polynesia, which clean other fish by eating the parasites from their skin, mouth and gills. This is mutually beneficial behavior, exchanging nutrition for cleansing.

But the researchers found that every once in a while, a cleaner fish would take a nip of mucus from the skin of the other fish.

That bite can inflict harm because mucus is part of the client fish's immune system.

But, cleaner fish only took such bites when they were in distant parts of their home range and were unlikely to re-encounter said fish. In areas where they often swim and where re-encounters were more likely, the cleaner fish ate only the parasites.

"Our results provide the first evidence supporting the notion that animals may have the ability to flexibly adjust levels of cooperation with individual partners to account for future payoffs," the researchers wrote in the journal Current Biology.

- The Washington Post