By being able to wait for better food, cuttlefish — the squishy sea creatures similar to octopuses and squids — showed self-control that's linked to the higher intelligence of primates.
It was part of an experiment by Alex Schnell from the University of Cambridge and colleagues.
"What surprised me the most was that the level of self-control shown by our cuttlefish was quite advanced," she tells Lulu Garcia-Navarro on Weekend Edition.
The experiment was essentially a take on the classic "marshmallow" experiment from the 1960s. In that experiment, young children were presented with one marshmallow and told that if they can resist eating it, unsupervised, for several minutes, they will get two marshmallows. But if they eat it that's all they get.
The conventional wisdom has been that children who are able to delay gratification do better on tests and are more successful later in life. (There are of course many caveats when talking about the human experiments.)
To adapt the experiment for cuttlefish, the researchers first figured out the cuttlefish's favorite food: live grass shrimp; and their second-favorite food: a piece of king prawn. Instead of choosing one or two marshmallows, the cuttlefish had to choose either their favorite food or second-favorite food.
"Each of the food items were placed in clear chambers within their tank," Schnell says. "One chamber would open immediately, whereas the other chamber would only open after a delay."
It "essentially tested whether they could resist the temptation of their second preference food item and wait for their preferred food item."
The cuttlefish learned to wait.
"Animals like rats, chickens and pigeons, they find it difficult to resist temptation and have relatively lower levels of self-control, only waiting for several seconds," Schnell says. "Whereas animals such as chimpanzees, crows and parrots, they show more advanced self-control and they can wait up to several minutes. And the cuttlefish in our study waited up to between 50 to 130 seconds."
Animals that are able to exert self-control in this way have advantages. For example, animals can hide food to eat later, but they have to resist the urge to eat now.
The researchers say the experiment is the first evidence so far of this type of cognitive ability in an invertebrate.
In cuttlefish, Schnell thinks the delayed gratification relates to their lifestyle. They are masters of camouflage; they are able to blend into their environment and can stay perfectly still for long periods of time to avoid predators.
Then they forage for food in brief outings. "Individuals who wait for better-quality prey could forage more efficiently at the same time as limiting their exposure to predators," Schnell writes.
But to take things a step further, the researchers did a second experiment. They put colored markers into the tank and taught the cuttlefish to associate a certain color marker with food, by dropping food when the cuttlefish went to the marker. Then they swapped the colors.
The second experiment was to test the animals' "learning performance." The cuttlefish that were quicker to learn to associate and reassociate the markers with food were considered better learners.
They found the cuttlefish that were able to delay gratification the most also happened to be the ones that were better at learning. It's the "first demonstration of a link between self-control and learning performance outside of the primate lineage," Schnell writes.
Finding these similarities between cuttlefish and primates "is an important piece of the evolutionary puzzle," she adds.
Hence, the squishy cuttlefish is leading scientists a step closer to understanding more about the origins of intelligence.
Rosemary Misdary and Martha Ann Overland produced and edited the audio interview.
LULU GARCIA-NAVARRO, HOST:
In the search for the origin of intelligence, a team of scientists at Cambridge University turned to the cuttlefish for answers. The rounder cousin of the squid surprised them not with its tentacles or venomous ink, but with its self-control. Because self-control shows strategy and planning, it's considered a sign of intelligence. Alex Schnell is a behavioral ecologist and the lead author of the study, and she joins us now from Sydney, Australia.
ALEX SCHNELL: Hi. Thank you so much for having me, Lulu.
GARCIA-NAVARRO: So your study reminds me of the marshmallow experiment that was conducted back in the '70s to test the self-control of children.
SCHNELL: Absolutely. That's where the study is adapted from. A team of scientists at Stanford University provided children with a marshmallow experiment, and they were offered one marshmallow that they could eat. But if they didn't eat it and were able to wait for 15 minutes, they were offered two marshmallows. About 50% of the toddlers caved in, and they would eat the marshmallow. And the other 50% would hold out for two marshmallows. There has been this kind of idea and increasing evidence to suggest that self-control is linked to general intelligence.
GARCIA-NAVARRO: So tell me how this linked to your experiment with the cuttlefish. What did you do to the cuttlefish? I'm sure you didn't give them a marshmallow.
SCHNELL: Absolutely. We first tested their food preferences for different foods that they would commonly eat. And from those results, we used their first-preference prey and their second-preference prey and essentially designed a test where they had to choose between the two preys. But each of the food items were placed in clear chambers within their tank. One chamber would open immediately, whereas the other chamber would only open after a delay. And that chamber contained their first preference. Once they made a choice between one of the food items, the other choice was taken away. And so this essentially tested whether they could resist the temptation of their second-preference food item and wait.
GARCIA-NAVARRO: Why cuttlefish?
SCHNELL: Seeing as cuttlefish can remember past events, I wondered whether they could also plan for the future, a type of intelligence that is quite sophisticated. And then my anecdotal inspiration stems from an experience that I had in the marine lab where a cuttlefish got into the frequent habit of drenching me with a cascade of water.
SCHNELL: Yeah. Most mornings, it happened when I would walk past her tank. The interesting thing is she only squirted me in the morning when it was time to participate in experiments, and she refrained from squirting me in the evening when I would be in the lab to feed her dinner.
SCHNELL: Is this selective squirting? Is she simply learning to associate my morning visits with something she didn't like, or is there an element of self-control and planning involved?
GARCIA-NAVARRO: And what did your study find?
SCHNELL: Yes, cuttlefish have the capacity for self-control. And what surprised me the most was that the level of self-control shown by adult cuttlefish was quite advanced. Animals like rats, chickens and pigeons - they find it difficult to resist temptation and have relatively lower levels of self-control, only waiting for several seconds, whereas animals such as chimpanzees, crows and parrots - they show more advanced self-control, and they can wait up to several minutes. And the cuttlefish in our study waited up to between 50 to 130 seconds.
GARCIA-NAVARRO: Makes me think I'm not going to eat any more cuttlefish.
SCHNELL: Yeah. When I started my PhD and I was working on cuttlefish, I took cuttlefish off the menu.
GARCIA-NAVARRO: Alex Schnell is a behavioral ecologist at Cambridge University. The study was released this month in a biological sciences journal published by the Royal Society.
Thank you so much.
SCHNELL: Thank you, Lulu. Transcript provided by NPR, Copyright NPR.