Cuttlefish Pass a Marshmallow Test
Given a choice between shrimp now or better shrimp later, cuttlefish waited up to two minutes — and the better waiters learned faster too.
In 2021, Alexandra Schnell and colleagues at the University of Cambridge adapted Walter Mischel's marshmallow test for cuttlefish. Six Sepia officinalis were trained to associate two chambers with different rewards — a chunk of king prawn versus a live grass shrimp, which cuttlefish prefer. They could see the prawn immediately, but the shrimp would only appear after a delay. Eating the prawn canceled the wait.
The cuttlefish waited. Each one held out for 50 to 130 seconds before the better food was delivered. In control trials where the shrimp would never arrive, they ate the prawn promptly. They were not indiscriminate; they were tracking the odds.
The team also tested learning. Cuttlefish that waited longer in the self-control task also learned faster in a visual reversal-learning task — figuring out that the previously-rewarded cue was now the punished one, and switching. In vertebrates, this link between delay tolerance and cognitive flexibility shows up in children, chimps, and corvids. It hadn't been demonstrated in any invertebrate.
The result matters because cuttlefish diverged from the vertebrate lineage more than 500 million years ago. Their brains are built on a different plan, with a donut-shaped central nervous system looping around the esophagus. Finding self-control and flexibility in them suggests the ability to delay gratification is either convergent — evolving more than once — or very old. Schnell's paper appeared in Proceedings of the Royal Society B. The headline that ran in half the press — "cuttlefish smarter than children" — was wrong in the direction of being fun.
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