Entering the marine lab each morning to do her experiments, Alex Schnell was frequently doused with water by one of her cuttlefish subjects—a behavior that the University of Cambridge comparative psychologist interpreted as acting out. Come dinnertime, when she didn’t run experiments, the cheeky cephalopod never squirted, Schnell noticed. “This selective squirting made me start questioning whether the cuttlefish had simply learned to associate my morning visits with something bad happening or whether there was an element of self-control or planning involved.”
Schnell and her colleagues designed an experiment to test whether cuttlefish could plan ahead, specifically, by resisting the temptation of a tasty treat in exchange for an even tastier one. In a study published March 3 in Proceedings of the Royal Society B, the team found that the invertebrates delayed gratification for up to two minutes or more, a feat on par with chimpanzees and crows. Schnell speaks with The Scientist about what cuttlefish self-control suggests about cephalopod cognition and the evolution of human intelligence.
The Scientist: How did you get interested in studying cuttlefish?
Alex Schnell: I have a background in marine science and I became really interested in cephalopod behavior, how cephalopods—which include octopus, cuttlefish, and squid—communicate with one another by changing patterns of their skin. By studying that throughout my PhD, I was looking at how they communicate particularly during aggressive interactions and how they make decisions about whether to withdraw from a fight or whether to continue fighting. And then that decision-making aspect of my PhD research led more into their cognitive abilities: what type of learning and memory abilities these animals might have and if there are any similarities that we might find between this group of animals and the more commonly studied chimps, crows, and parrots.
TS: What motivated you to do this particular research?
AS: A few years ago, some of my colleagues, which include my current supervisor Professor Nicola Clayton and my former supervisor Dr. Christelle Jozet-Alvaes, discovered that cuttlefish could retrieve unique memory experiences—by that I mean something that specifically occurred to that particular individual. They were able to retrieve these memories and use them to fine tune their foraging.
This type of memory is called episodic-like memory, and it was once thought to be unique to humans. But recollecting past memories has since been discovered in rodents, brainy birds—like crows, jays, ravens—and apes. And then, of course, cuttlefish. Recollecting past memories is thought to have evolved so that humans and animals can plan for the future. It essentially acts as a database to predict future events.
Seeing as cuttlefish can remember past events, I started wondering whether they can plan for the future. That is a very sophisticated type of intelligence. But before asking that specific question, my colleagues and I first needed to ask whether cuttlefish have the capacity to exert self-control because self-control is a really important prerequisite for future planning. In order to plan for the future and plan for better outcomes in the future, individuals needed to resist temptation in the present moment.
TS: Do cuttlefish have different personalities or do they behave differently?
AS: Yes, they show a lot of character, and each individual has different idiosyncrasies. Within my subjects, I had ones that were a lot more patient than others. Some individuals were able to resist temptation for nearly double the length [of time compared with] other individuals. We also had differences in their eagerness to participate in the experiment. I started with a sample size of eight, and then two individuals decided they did not want to participate in this experiment halfway through. They wouldn’t settle at the bottom of the aquarium tank [for the experiment to start] and refused any type of food. So you do see a lot of differences between the subjects.
TS: Can you tell me about what experiments you did and what were your main findings?
AS: The start of the study began with a food preference test. . . . We figured out what their first preference was and what their second preference was. Then we conducted the self-control experiment, which is very much based on the famous psychology experiment conducted in children in the 1970s—the marshmallow test—where children were offered one marshmallow and they could eat it, but if they were able to wait 15 minutes they would earn a second marshmallow. Obviously, we didn’t use much marshmallows because cuttlefish wouldn’t find that a tempting reward; we used their second preference and their first preference.
Each individual has different idiosyncrasies. Within my subjects, I had ones that were a lot more patient than others.
All of them preferred a live grass shrimp, which is a see-through, very small shrimp, but they also liked prawn meat. . . . We can’t communicate with cuttlefish, so we can’t tell them that if they don’t eat the prawn meat, they’ll get the live shrimp, so we had to train them to learn about the accessibility of different clear chambers that were placed in their tank. One chamber with a particular visual shape on it meant that the minute the food was placed in their chamber, that door would open. Another chamber with a different visual cue meant that when food was placed in that chamber, there would be a delay before the chamber door would open. Initially, the cuttlefish would swim up to this chamber, they’d see the food inside and they’d try to attack it. But over time, they learned that one chamber meant immediate access, and the other chamber meant delayed access.
During the test phase, we presented them with both chambers at the same time and they were given the choice to choose one over the other. They could either have the immediate reward, which was the second preference or they could hold out for their preferred food that was delayed. We started the delays at ten seconds and increased that delay by increments of ten seconds. I should also mention that if they chose their immediate reward, the preferred reward was taken away, so they quickly learned that they could only choose one out of the two options.
TS: How good were they at waiting for this preferred food?
AS: They would wait one hundred percent of the time at ten seconds, twenty seconds, thirty seconds. As I increased the delay beyond thirty seconds, you could see that some of the individuals were struggling to resist the temptation of that second preferred food, and you’d see them sometimes wait for half the amount of time and then cave. My best subject waited for one hundred thirty seconds; my worst subject, his maximum wait time was fifty seconds.
In some instances, the cuttlefish would slightly turn their body away from the immediate option as if to distract themselves from that temptation.
You see a range, and that’s pretty common amongst other animals as well. . . . There is evidence of self-control in a range of diverse animals, but tolerance to temptation varies. For instance, animals like rats, chickens, and pigeons, they find it really difficult to resist temptation and they might only wait several seconds . . . whereas animals like chimpanzees, crows, and parrots show more advanced self-control and they can wait up to several minutes for food that they prefer. The cuttlefish in our study showed comparable levels to the latter group, and that was particularly surprising.
TS: You mentioned that some of the cuttlefish seemed to be struggling to delay their gratification. What did that look like?
AS: In some instances, the cuttlefish would slightly turn their body away from the immediate option as if to distract themselves from that temptation. You see that in other animals. Dogs and parrots will close their eyes or look away, and the same with jays. Children and chimpanzees sometimes distract themselves by playing with a different object. So it was quite interesting to see this potentially self-distracting behavior in cuttlefish.
TS: I think another one of your findings was that the time they waited was correlated with another measure of intelligence. Can you tell me about that test and why you chose that measure of intelligence?
AS: We found that there was a link between a subject’s learning performance and their ability to delay gratification. . . . That link has been demonstrated in humans and chimpanzees before. Individuals that exert greater self-control generally perform better in academic tests or show better cognitive performance in a range of different cognitive tests.
We investigated cognitive performance in the form of learning. We presented cuttlefish with a simple reversal learning task where two plastic markers were placed in their tank that were different in color: one was gray and one was white. The cuttlefish had to learn to associate an edible reward with one color, and once they learned that association, we reversed the reward contingency so they had to learn that the edible reward was now associated with the reverse color. What we found was that the individuals who learned the first association and the reverse association quicker were also better at exerting self-control.
Learning performance is an indicator of general intelligence, but one of the limitations is that we’ve conducted just one type of experiment that indicates general intelligence. A study that showed this link outside of humans in chimps showed that self-control was linked to performance in a range of different cognitive tests—how chimps performed in spatial memory tests, how they performed in causal reasoning tests or object permanence. The goal would be to do a similar thing with cuttlefish to see if we can find any more correlations in different tests.
TS: What do your findings contribute to our understanding of cephalopod intelligence?
AS: It contributes to even more than cephalopod intelligence; it kind of updates our understanding of the evolution of human intelligence and specifically why and how self-control might have evolved.
Our current understanding has very much been based on the evolutionary pressures that are relevant to long-lived social species. For long-lived social species, the benefits of self-control might be obvious. For example, apes and brainy birds—including crows and parrots—live long lives and they’re sociable, so they might resist temptation in the present moment to obtain better outcomes in the future and live a longer life. These groups of animals might also resist temptation [in order] to help a social partner and that might strengthen social bonds and also help them receive reciprocated favors in the future from that social partner.
Another theory is that self-control might have evolved as a function of tool building. These animals might resist hunting or foraging in the present moment so that they have the time to build a functional tool and optimize their hunting behavior.
It also opens up this avenue to start looking for different types of cognition in cuttlefish that are very much classified as more sophisticated intelligence.
All of those theories don’t apply to cuttlefish because they haven’t experienced the same pressures. Finding self-control in cuttlefish is a really extreme example of convergent evolution because they have really different evolutionary histories than the more commonly studied long-lived social species. They’re short-lived, they’re not social, and they don’t build tools. We speculate that cuttlefish might have evolved self-control to fine-tune their foraging. Cuttlefish are camouflaged for the majority of their time, they remain motionless to avoid detection from predators. These really long periods of camouflage are broken when the animal needs to eat, so perhaps they evolved self-control to optimize these hunting excursions because waiting for preferred food might speed up their hunting excursions and also limit their exposure to predators.
It also opens up this avenue to start looking for different types of cognition in cuttlefish that are very much classified as more sophisticated intelligence. Self-control is thought to be the fundamental basis for complex decision-making and planning for the future. So finding self-control in cuttlefish opens up this opportunity to look for those other types of cognitive abilities in cuttlefish.
TS: What do we know about the differences between cuttlefish and other cephalopod cognition compared to mammals and other vertebrates?
AS: Cephalopods have been in the spotlight for a long time in terms of their camouflage and neurobiology and behavior, but I think we’re at the beginning of really testing their cognition in comparable paradigms [to those] that are used in the large-brained vertebrates. We know that [cuttlefish] are really efficient learners and they have both have short- and long-term memory. But I think it’s only been in the past ten years that we’re starting to adapt the experiments that we use in apes and members of the crow family so that they can be tested on cephalopods to see if there are any similarities or differences within the way that they solve these tasks.
TS: Do you have plans to follow up this study with other cephalopods?
AS: Some colleagues of mine are looking into octopus cognition. . . . I think cuttlefish are my preference because octopus are a little trickier to work with. I mentioned before that cuttlefish have their little idiosyncrasies and they show strong personality differences. I feel like that’s even more so in octopus. If an octopus does not want to participate in an experiment, it’s really difficult to urge it to participate. All participation is voluntary and some octopus just refuse completely. They are also really hard to house. I’ve had a number of escapees when I used to work with octopus. No matter how secure you make the aquarium, you’ll sometimes walk into the aquarium in the morning and you have a Houdini octopus that has escaped and is on its way back into the ocean. I think cuttlefish are definitely my preference and I do have plans to continue these kinds of experiments in cuttlefish.
A.K. Schnell et al., “Cuttlefish exert self-control in a delay of gratification task,” Proc R Soc B, doi:10.1098/rspb.2020.3161, 2021.
Editor’s note: This interview was edited for brevity.