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While many vertebrates—chimps, dolphins, ravens, elephants—are known for their intelligence, invertebrates are often seen as alien. This perception changed when a cuttlefish successfully completed a cognitive test originally designed for humans.
In a 2021 study published in the Proceedings of the Royal Society B, researchers from Cambridge adapted the classic Stanford Marshmallow Test to the aquatic world. The original experiment, begun in the 1970s, offered children a choice between one marshmallow now or two after a 15‑minute wait. Children who waited were later found to achieve higher academic success, linking self‑control to intelligence. Although the methodology has been refined, the test remains a landmark in cognitive science.
Cambridge scientists applied the same principles to cuttlefish. Instead of marshmallows, they used prawns and shrimp; instead of verbal prompts, the animals were trained to respond to symbolic cues. The results were striking: cuttlefish that exhibited greater self‑control performed better on subsequent learning tasks—performance comparable to that seen in large‑brained vertebrates such as chimpanzees, according to lead author Alexandra Schnell of the University of Chicago Marine Biological Laboratory.
The 2021 study was not the first to show cuttlefish passing the marshmallow test. A 2020 experiment also demonstrated self‑control in cephalopods. Researchers offered cuttlefish a choice between crab and shrimp, finding that all 29 preferred shrimp. They then trained a group to expect a strict feeding schedule—crab for breakfast, shrimp for dinner. The cuttlefish learned to fast in the morning, saving energy for the tastier shrimp dinner. This delayed gratification behavior is one of the traits cognitive scientists associate with higher intelligence.
To eliminate alternative explanations, Schnell and colleagues refined the test. They trained cuttlefish to associate specific symbols with timers: a transparent container marked with a circle opened immediately, while a triangle signaled a delay. A dead prawn was placed in the circle‑marked container and a live shrimp (the cuttlefish’s favorite) behind the triangle. Choosing the prawn would permanently lock the shrimp container. All six test cuttlefish, already trained to recognize the triangle as “wait,” successfully resisted the temptation—some waiting up to 130 seconds. These “star students” also excelled in subsequent learning tasks, underscoring the cognitive parallels between humans and cuttlefish.
Such findings challenge the notion that invertebrates are cognitively primitive. Even if we prefer marshmallows over live shrimp, the evidence shows that cuttlefish possess sophisticated self‑control mechanisms comparable to those of vertebrates.
