Writing this debut blog post initially felt like a lot of pressure. I wanted to pick something relevant, something personal, and something that would pique the interest of everyone who reads this. I have two words for all of you: Cuttle. Fish. (It’s actually 1 word, but that wasn’t dramatic enough). I know what you’re thinking: “Katharine, you study the neuroscience of the bladder, why look into an article on cuttlefish?” The answer to that is two-fold. First, my late father who passed away in 2019, had a Ph.D in Evolutionary Psychology and taught at a University in Upstate New York for 30 years. The cuttlefish was one of his favorite animals to use to understand many theories within evolutionary psychology, so much so, that in one of his seminar classes, everyone purchased matching shirts with cuttlefish puns on them. And if that isn’t reason enough, a recent experiment by Schnell and colleagues out of the University of Cambridge suggests that these invertebrates can exert self-control similar to levels seen in larger-brained vertebrates.
Cuttlefish are marine molluscs belonging to the same class of animals as squid and octopus. Even before this study was published, cuttlefish were known to be one of the most intelligent invertebrates. Though brain size isn’t always correlative to intelligence (exhibit A: the blue whale), cuttlefish have one of the largest brain-to-body size ratios of all invertebrates. Though intelligence is multi-faceted and made up of several components, the ability to exert self-control has been linked to learning performance in numerous species, including humans. This theory has been tested for decades in human children using the “marshmallow test” (aka the Stanford Marshmallow Experiment). In this test, children were given a choice: they could have one marshmallow immediately, or they could wait 15 minutes and have two marshmallows. In the original study, children that exhibited delayed gratification and the self-control to wait and get the two marshmallows were shown to be more successful later in life as evidenced by metrics like SAT scores and even BMI. As a brief side note, in the time since these conclusions were drawn, additional research into delayed gratification using this experimental design has shown that being able to have the type of self-control necessary to choose the two marshmallows is more of a function of socioeconomic background than sheer willpower. I digress, that’s probably its own blog post.
Luckily for this study, cuttlefish do not have socioeconomic backgrounds (nor several other confounding variables) so the researchers adapted the marshmallow experiment for the cuttlefish. Each cuttlefish was presented with two options, behind door number one was a king prawn, a mediocre food in the eyes of a cuttlefish. Behind door number two was the holy grail of cuttlefish prey: the live grass shrimp. Unlike previous studies done in rats and pigeons, the cuttlefish were able to wait 50-130 seconds for the more desirable shrimp. In a follow-up study, the cuttlefish that were able to resist the urge to eat the mediocre shrimp and wait for the more desirable prey, were also shown to learn quicker and more efficiently in an associative learning task. The authors note that this positive association between self-control and learning performance is the first seen in non-primate animals.
This research provides meaningful results as well as open questions for future research. Socio-ecological factors, like cooperation and relationship maintenance, are the main drivers for self-control in several species. However, many of these factors do not apply to cuttlefish, since they are not at all social creatures: they do not work cooperatively, they exhibit no parental care, and some species of cuttlefish cannot even recognize the opposite sex (which keeps mating interesting!). Given that, it is doubtful that social factors are driving the effect of self-control. Instead, the authors suggest the alternative explanation that cuttlefish evolved to possess delayed gratification due the specific ways that they forage for food. Though further research should delve into this further, this may suggest that cuttlefish are able to execute higher order cognitive functions, like making plans. If self-control and future planning are evolutionarily linked in the cuttlefish, and even if they are not, this would provide information relevant to all species about the evolution of intelligence.
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