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Cuttlefish show they're as smart as kids in 'marshmallow test' study

The marine mollusks demonstrate they're able to delay gratification for the reward of a better snack.

A broadclub cuttlefish swims at Australia's Great Barrier Reef in 2015.
At Australia's Great Barrier Reef in 2015, a broadclub cuttlefish hunts for a pretzel stick. Or was it a marshmallow?
Reinhard Dirscherl/Getty Images

Treats can be hard to resist, no matter what your age or species. But a new study reveals that cuttlefish -- yes, the marine mollusk -- can adapt to a well-known psychological test given to human children, and learn to defer gratification in order to snag a better snack.

Known to some as the Stanford Marshmallow Test, the original test was a study on delayed gratification led by psychologist and professor Walter Mischel, who began it in 1970 and published his results in 1972. Participating children were offered a pretzel stick or marshmallow but told if they could wait for the treat, they'd receive two of the item. Follow-up studies examined whether the children who could successfully wait ended up with better life outcomes.

"Cuttlefish in the present study were all able to wait for the better reward and tolerated delays for up to 50-130 seconds, which is comparable to what we see in large-brained vertebrates such as chimpanzees, crows and parrots," said lead author Alexandra Schnell of the University of Cambridge in England.

Cuttlefish, of course, can't simply be offered the verbal choice of two different snacks. In the study, they were shown two different food options behind clear walls. One showed raw king prawn, and the other their preferred food of live grass shrimp. The cuttlefish were trained that certain symbols on the chamber doors meant the door would either open right away, open after a delay, or not open at all.

The prawn door opened right away, but if the cuttlefish ate it, the shrimp option was taken away. If the prawn door opened and the cuttlefish left it alone, they eventually were given a chance at the shrimp.

The scientists don't know why the cuttlefish developed such self-control, but they theorize it might be related to the fact that they're vulnerable to ocean predators, so it benefits them to stay hidden until the good chow shows up.

"Cuttlefish spend most of their time camouflaging, sitting and waiting, punctuated by brief periods of foraging," Schnell said in a statement. "They break camouflage when they forage, so they are exposed to every predator in the ocean that wants to eat them. We speculate that delayed gratification may have evolved as a byproduct of this, so the cuttlefish can optimize foraging by waiting to choose better quality food."