It is a staple of language classes and parental lectures: Say thank you.

It is one of the first phrases you learn in a new language, and one whose importance is drummed into children through repeat readings of books like “The Berenstain Bears Say Please and Thank You,” “Richard Scarry’s Please and Thank You Book” and “Thank You, Mr. Panda.”

But as it turns out, we say thank you far less often than we might think.

A new study of everyday language use around the world has found that, in informal settings, people almost always complied with requests for an object, service or help. For their efforts, they received expressions of gratitude only rarely — in about one of 20 occasions.

This might seem like a damning verdict on human nature, or evidence of a global pandemic of rudeness. But to the researchers, it is good news.

“Our basic stance is one of reciprocity,” said Nick Enfield, a linguist at the University of Sydney, who led the study. “When we ask people to help us, the default is that they will.”

The study, published in the journal Royal Society Open Science, is part of a broader effort to look at language as a tool grounded primarily in social interaction rather than as a vehicle for the expression of ideas. Enfield and his team looked at interactions in eight languages: English, Italian, Polish, Russian, Lao, Cha’palaa (spoken in Ecuador), Murrinhpatha (an aboriginal language in Australia) and Siwu (spoken in Ghana).

The researchers focused on casual daily interactions among people who knew each other, as captured by unattended cameras set up in homes or community areas. Any verbal expressions of gratitude (including phrases like “good job” or “sweet”) were counted as expressions of thanks.

People signal the need for assistance frequently: about every minute and a half, according to the researchers’ samples. And they usually get it: Requests were complied with about seven times more often than not.

But those who cooperated were very rarely thanked, nor did they seem to expect it. When no thanks were given, the omission was very rarely commented on. On the other hand, when people did not comply with a request, they usually gave an explanation.

“It’s completely asymmetrical,” Enfield said. “People typically don’t give their reasons when they comply. This just underlines the fact that cooperation is the default mode.”

While the study appears to be the first to gather such extensive cross-cultural data on how often people say thank you (as opposed to how often they think they do), the low frequency of thanks does not come as a big surprise to researchers who study reciprocal behavior from an evolutionary point of view.

“We expect help from close relationships — family and friends, but especially family,” said Robin Dunbar, an anthropologist at Oxford who was not involved with the study. “That we take that help for granted is indeed interesting, because it risks putting such relationships under strain.”

Enfield and his colleagues did find some variations across languages. Speakers of English and Italian verbalized thanks significantly more often than speakers of the other languages, but still quite infrequently — in only one of seven instances where a request was complied with.

The researchers attribute this to what they call the strong “cultural ideology of politeness” in Western European cultures. This does not mean, however, that English or Italian speakers are actually more grateful.

“Expressing gratitude and feeling gratitude are not the same thing,” Enfield said.

The implications of giving thanks also vary across cultures. In some languages, a phrase we might translate as “thank you” is reserved for truly momentous favors, like saving someone’s life. In others, frequent thank yous can seem strange, or even (as in some South Asian languages) insulting.