There are certain things most Americans expect to encounter on Thursday: Turkey. Mashed potatoes. A lazy afternoon. Too many lagers. A belly ache. A nod toward the things we’re thankful for.

But the one thing we should perhaps be most thankful for may slip under the radar, and that is the incredible human brain, which kicks into high gear on this annual day of indulgence and gratitude.

In an op-ed published last Saturday in The Boston Globe titled Gratitude Pays Big Dividends, psychology professor Dave DeSteno discusses how human emotions have evolved to “serve socially adaptive functions.” He says we tend to think of gratitude in terms of the past: the things that have already happened that we’re thankful for now. But in fact, DeSteno argues, gratitude may have more to do with the future.

DeSteno’s lab has shown that people who have recently experienced kindness from someone else are more likely to pass that kindness along to another, even a stranger. “The more gratitude people feel,” he writes, “the more likely it is they’ll help anyone, even if it’s someone they’ve never laid eyes on before.” For that reason, he sees gratitude as a social strategy that helps build resilient communities. What goes around really does come around and our brains seem to know it even if we sometimes forget it.

On Thanksgiving Day we reflect on our relationships and the things we have — both material and otherwise.. But it doesn’t seem to matter what we’re thankful for — as long as we’re feeling gratitude, we’re more likely to help our fellow humans.

Of course, turkey day isn’t always terribly conducive to being helpful — if that help requires a considerable amount of physical energy. That’s because it’s all being funneled off to do the seemingly more important job (in an evolutionary sense) of digestion. Tryptophan is the amino acid that’s often pegged as the cause for the overwhelming exhaustion that sets in after the massive, gravy smothered, turkey dinner we like to indulge in once a year. But, says chemistry and chemical biology professor and chair Graham Jones, this is a common misconception.

“Indeed, while it is true that tryptophan has sleep inducing effects, and its metabolites — seratonin and melatonin — are sleep regulators, it does not account for the drowsiness we often experience.” He says that drowsiness would require eating a heck of a lot more turkey than even the most fervent mouth stuffers among us could consume: close to 40 pounds worth.

The more likely culprits of our food-induced coma are the fats and carbohydrates the meal contains, according to Jones. “Carbohydrates make the pancreas secrete more insulin, which in turn stimulates production of serotonin,” he explains. “Digestion of fats results in redistribution of blood flow, also resulting in lowering of our energy levels and increased sedative feeling.” Not to mention the beers and the wine and whatever other bacchanalian treats you imbibe, which are all central nervous systems depressors.

As you relax after the food tomorrow, it might be a good idea to keep all of this in mind. Even if someone hasn’t recently paid you a kindness, you still have quite a bit to be thankful for, as you sit in the Barcalounger, letting your neurotransmitters and your hormones and your enzymes work their bottoms off to deal with your over-indulgence. After all, any gratitude you can muster is a payment into society’s future.