We humans have much more self-discipline than other animals. We can and do set goals—losing 25 pounds, going to college—and then go without certain pleasures to achieve those goals. We’re far from perfect at this, but there’s no question that better self-control sets us apart from more lowly beasts.
Scientists have long argued that delaying gratification requires a sense of “self.” Having a sense of personal identity allows us to compare what we are today, at this very moment, with what we want to be—an idealized self. Aspiring to this idealized self is what fosters uniquely human self-control powers.
Well maybe—or maybe not. New research is now suggesting a much more primitive explanation for our powers of self-discipline—one that brings us down a notch or two
in the animal kingdom. Indeed, it appears that, even with our lofty goals, we may rely on the same basic biological mechanism for self-discipline as our four-legged best friends. Here’s the science.
Psychological scientist Holly Miller and her colleagues at the University of Kentucky knew from previous research that human self-control relies on the brain’s “executive” powers, which coordinate thought and action. It’s further known that this kind of cognitive processing is fueled by glucose, and that depletion of the brain’s fuel supply compromises self-discipline. But is this a uniquely human system? Or do less evolved animals rely on sugar-powered executive powers as well?
To find out, Miller recruited a group of dogs ranging in age from ten months to more than ten years old. Some were pure breeds, like Australian shepherds and Vizlas, while others were mutts. The dogs were all familiar with a toy called a Tug-a-Jug, which is just a clear cylinder with treats inside; dogs can easily manipulate the Tug-a-Jug to get a tasty payoff. In the experiment, some of the dogs were ordered by their owners to “sit” and “stay” for ten minutes. That’s a long time to sit still; it was meant to exhaust the hounds mentally, and thus to deplete their fuel reserves. The other dogs, the controls, merely sat in a cage for ten minutes.
Then all the dogs were given the familiar Tug-a-Jug, except that it had been altered so that it was now impossible to get the treats out. The hungry dogs could see and hear the treats—but not get at them. The idea was to see if the previous demand for self-discipline made the dogs less, well, dogged in working for the treats. And it did, unmistakably. Compared to the dogs who had simply been caged, those who had stayed still for ten minutes gave up much more quickly—after less than a minute, compared to more than two minutes for the controls. In other words, exerting self-discipline had used up much of their sugar supply—and weakened the executive powers needed for goal-directed effort.
Executive powers? In old Shep? These findings suggest that self-control may not be a crowning psychological achievement of humanity, and indeed may have nothing to do with self-awareness. It may simply be biology—and beastly biology at that. These are humbling results, so the scientists decided to recheck them in a different way. In a second experiment, they recruited another group of dogs, this time including Shetland sheepdogs and border collies. As before, some of the dogs sat and stayed for ten minutes while the others were caged. But this time, half of the obedient dogs got a sugar drink following the exercise, while others got an artificially sweetened drink. Miller basically wanted to see if she could restore the dogs’ executive powers by refueling them.
Which is exactly what happened. As reported in the April issue of the journal Psychological Science, the dogs who exerted self-control, then got replenished with sugar, were just like the dogs who had not been exhausted to begin with. They persisted just as much with the Tug-a-Jug, even though it was frustrating and demanding to do so. The depleted dogs who were not replenished gave up in short order. In short, they all acted just like humans.
So we’re not unique—at least not in this regard. It appears that hallmark sense of human identity—our selfhood—is not a prerequisite for self-discipline. Whatever it is that makes us go to the gym and save for college is fueled by simple sugar—much like our hound’s decision to sit still and stay.
Articles from “We’re Only Human” also run regularly in The Huffington Post and in Scientific American Mind. Wray Herbert’s book, On Second Thought: Outsmarting Your Mind’s Hard-Wired Habits, will be published by Crown in September.
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