Ever seen images of preschoolers staring longingly at a single marshmallow? Chances are, you caught a glimpse of the so-called marshmallow test. Conducted about 50 years ago, the experiment was designed to examine preschoolers' ability to delay gratification when presented with a choice of having one marshmallow now or waiting a period of time and having two marshmallows later.
The marshmallow test was more than just amusing video footage. Researchers later suggested that passing it could be an early indicator of a child's future success in school, occupation and even life in general. Those findings have come under scrutiny in recent years, but the study remains one of the most beloved pieces of social-science research.
It also got researchers wondering whether a similar test of willpower could be duplicated in non-human animals — and even sea creatures like cuttlefish. And if so, could it indicate which creatures would be better suited for survival?
How the Marshmallow Test Worked
The marshmallow test, also called the Stanford Marshmallow Experiment, involved a series of studies by Stanford University psychologist Walter Mishel, to better understand a child's ability to delay gratification. The research, published in 1972, included hundreds of children, most of whom were between the ages of 4 and 5. Each child was presented with a dilemma: Have one marshmallow now or wait 15 minutes and have double the number of confections. After being posed the question by the researchers, the children were left alone with the marshmallow to contemplate their decision.
Some children ate the marshmallow as soon as the researcher left the room while others squirmed in their seats trying to resist the temptation. As you can imagine, video footage of the experiment is excruciatingly cute.
Delayed gratification "is an important developmental milestone, but also one that developmental psychologists realized was not equally evident in all children," says Michael James Beran, professor of psychology and co-director of the Language Research Center at Georgia State University, in an email. "And so, then the question was about what might explain why some kids were better [at the test]. Turns out, there are a lot of environmental factors that affect how well a child performs."
What Did the Marshmallow Test Show Long-Term?
The marshmallow test was thrust back into conversation when a 1990 follow-up study on the child participants of the Stanford Marshmallow Experiment revealed that the test "related to a lot of things we care about tremendously as a society," Beran says. The test showed the ability to delay gratification was correlated with higher SAT scores, fewer behavioral problems and lower body mass index (BMI) among other quality of life measures.
How does delaying gratification lead to better outcomes? Beran offers these examples:
- Obesity: Eat chocolate cake any time you can or stick with raw veggies and lose 10 pounds over the next six months.
- Heart disease: Enjoy a cigarette now, or suffer through desire, but protect your heart and live more years later.
- STDs: Engage in unsafe sex now while aroused or avoid that temptation to ensure no need to be treated later for possible infection.
- Retirement: Bigger house now, new cars now, but then not enough money later (when in your 60s) to retire.
- Environment: Cut all those trees down today to sell and make a lot of money now, or sustainably harvest so that in 10 years you can do it again.
- Education: Party now, make Bs and Cs, or stay home and study to eventually earn As and have a better GPA to give you better job or grad school opportunities.
But in 2018, a new study threw the premise of the 1990 follow-up study under the bus. The original study involved less than 90 children, all of whom were enrolled in a Stanford preschool (many were children of Stanford students and professors.) The 2018 experiment was designed to be more representative of the general public with more than 900 children from different races, ethnicities and parental education level.
Researchers found only limited evidence to suggest that children who were able to delay their gratification in the marshmallow test fared better in life. Instead, they discovered a child's socioeconomic status (SES) to be a stronger indicator of long-term success.
"For example, it may be that children from lower SES families may perform worse, but for reasons that have to do more with those children having learned that waiting for things rarely works out, and so their environments might actually promote taking smaller rewards more immediately," Beran says. "This will continue to be debated, as it should, but it is true that the marshmallow test is diagnostic of things of great importance."
Can Animals Pass the Marshmallow Test?
Beran, who also authored the book "Self-Control in Animals and People," has focused his research on cognitive control and how children and nonhuman primates show self-control. His work encompasses delayed gratification and how both children and primates monitor how much they know or remember and then decide when they need help or seek more information. These activities, he explains, require making a deliberate choice.
Why study this in animals? There are two major reasons, argues Beran. "In itself, the question of self-control and delay of gratification (like the marshmallow test assesses) is a question about animal minds." By engaging in cognitive control, an animal is demonstrating that it is mentally processing the problem it is facing. And researchers can observe and begin to understand the animal's cognitive process.
The second reason is to study other species to better understand who we are. "We want to know if human language is special for delay of gratification, or if big brains are necessary, or culture is required," he says. "To better understand this, we need to see what other species can do."
Can animals pass the marshmallow test? Sometimes, Beran says. But humans do it at levels beyond the imagination of animals. Proof of humans' delayed gratification can be seen in farmers who give fields a year to stay fallow to increase future yields in later years rather than growing a faster yielding crop of less market value. Or stockholders who resist the urge to sell when prices fall, knowing they'll bounce back eventually.
"Chimpanzees are not doing this kind of delayed gratification (that we know of)," Beran says. "But, what it takes to wait five minutes to double your reward is presumably a basic, core process relevant to humans' capacity for extreme delay of gratification."
Beran created a version of the marshmallow test for chimps where they could wait for a better reward (delivered minutes later) or press a button to take a reward immediately. When they had to wait for a better reward (a banana rather than a carrot) they often did. Another test he developed tested whether chimps and other primates would leave an accumulation of food alone if the pile increased the longer it was left alone. Chimps were able to do this, using distraction techniques (like looking at a magazine) to let more candies accumulate.
There are several ways an animal's ability to delay gratification can indicate long-term success and, as a result, survival, Beran says. For example, a monkey wants food that's only available on the other side of an open field of tall grass and he impulsively runs toward it. But in doing so, he may not see a predator in the field and get killed, and thus never pass on his genes. "The hesitant, cautious monkey that pauses to look before moving through the field may see that predator," and survive, he says.
Tool use in animals is another example. To locate nuts, and hammer stones to crack those nuts, and then to hammer until a nut opens to provide calorie-dense food takes more time and effort than simply eating whatever is nearby, like fruit or a plant. "To get something better required waiting longer, and putting in more effort," he says.
Some low-ranking animals wait until more dominant animals have moved away before moving to a food source they have spotted. Had they not waited patiently, the dominant animal would have seen the food they were after and taken it. "To do this requires inhibitory control, and perhaps even some level of strategizing that 'I can get that later, once he has moved away and it is safer to approach,'" Beran says.
In March 2021, results of a marshmallow test with cuttlefish was published, which showed the mollusk was able to tolerate delays of 50 to 130 seconds to get its desired prey (live grass shrimp). It also showed that the cuttlefish able to wait the longest for their favorite foods also performed best during learning tests. This marked the first time a link had been shown between self-control and learning performance in a non-primate animal, the researchers said.