Yes, you do eat more at the holidays. Evolution trained you to.

If you reach for extra helpings of turkey and stuffing on Thanksgiving, don’t feel too self-conscious. Chances are, everyone else gathered at the table will pile more food onto their plates, too.

Blame the indulgence on one another, and our evolutionary wiring that dates back to our primitive days.

It's a real thing, and researchers call it the "social facilitation of eating" ― the tendency for people to eat more when they are with company than when they are alone. In fact, according to a recent British study, a meal size could be 29 to 48 percent larger when someone eats with other people, particularly when they are with friends and family, vs. people they don't know well.

Psychologist Helen Ruddock, an author of the study, said that, indeed, she eats more when she is with friends and family - "especially at Christmas, because there's always so much food available."

"I often eat beyond the point of fullness in social situations," Ruddock said.

Our tendency to eat more with companions goes back to the hunter-gatherer days, when people competed for resources, Ruddock said. This created a tension between wanting to get enough food for ourselves, and not wanting to look greedy. People would strike a balance by eating roughly the same amount as those around them.

"Individual group members are guided to match their behavior to others, promoting a larger meal than might otherwise be eaten in the absence of this social competition," the study states.

Of course, most of us aren't hunter-gatherers in the modern world, but the evolutionary roots still guide our eating habits, according to the study.

Ruddock and her colleagues at the University of Birmingham’s Eating Behaviour Research Group did a meta-analysis by examining 42 previous studies about social eating, which was published in the fall in the American Journal of Clinical Nutrition. The studies include those in which participants were observed eating alone and with others, and also those that examined people’s food diaries.

Researchers discovered that other species do the same. Animals, including chickens, rats and gerbils, also eat more when they are in a group, the study stated.

"This suggests it serves an ultimate purpose," the authors wrote.

While our close relations seem to have a big impact on our meal size - in part because the meal can go on for hours - the analysis found no major difference in food intake when people eat alone vs. with strangers and acquaintances.

Thanksgiving, with large quantities of comfort food and a celebratory vibe with loved ones, creates a perfect storm for stuffing ourselves with mashed potatoes, cranberry sauce and green bean casserole, said Tessie Tracy, an eating-psychology coach affiliated with the Boulder, Colo.-based Institute for the Psychology of Eating.

Tracy, who is not connected to the study, said that with friends and family, there's an expectation and also almost "an unspoken pressure" to eat a lot on holidays.

"Auntie says, 'Oh, you have to clear your plate,' " said Tracy, who coaches people to explore their relationship with food. "Auntie says, 'Oh, you're not going to try my pie?' "

She also said that, apart from family pressure, many of us just like to join the pack when there's a delicious sweet-potato casserole and fresh-baked rolls on the table.

"Everyone else is doing it, so I'm going to do it," Tracy said about our mind-set.

While this kind of eating once served a survival purpose, let's face it: Now that instinct can lead to indigestion and unwanted pounds. The authors recommend that future studies on the subject look at ways to enjoy social eating without being unhealthy.

That might be extra challenging at the holidays. There's some evidence that the Thanksgiving menu in particular fits well with the social facilitation of eating: Foods high in fat and protein - like turkey and gravy - have a strong association with eating more while with family and friends. One study found that the highest social-facilitation effects came from high-fat sweet foods such as pumpkin pie.

Whether it's the entree, dessert or the company - or likely, all three - the Thanksgiving meal is bound to foster a hearty appetite.

After all, it appears that we are just being human. And everyone else at the table probably will be polishing off their heaping plates, too.