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One-third of Americans aren’t able to name all of their grandparents, according to the genealogy website Ancestry.com. That proportion seems very, very high—it represents more than 100 million people. Can that estimate really be right?

Ancestry filled in some details when I inquired. The figure comes from a survey the company recently commissioned that polled 2,000 American adults who were “statistically representative” of the country’s overall population. In the survey, respondents were asked whether they knew the first names of their grandparents, and were not given any indication that they were being asked exclusively about their biological grandparents.

When I asked Ancestry for possible explanations of its finding, the company noted that many family trees are passed down orally, which might make familial details prone to being misremembered or forgotten. It also pointed out that a lot of kids grow up calling their grandparents nicknames or just “Grandma” or “Grandpa”—which could make it more likely that they’d blank when asked to provide their grandparents’ actual first names.  

In an attempt to better understand what else might be going on, I consulted some researchers who study family-related demographic patterns. Because these experts didn’t have access to the details of the survey’s methodology, their theories aren’t definitive explanations of Ancestry’s finding. But they are informed guesses, and together they capture the multifarious forms that American families take in the 21st century.

“I wouldn’t have any way of assessing the 1/3 number, but it doesn’t surprise me,” says Philip Cohen, a sociologist at the University of Maryland. Cohen and the two other researchers I emailed with brought up a variety of family structures that might complicate people’s awareness of their family line—single parenting, assisted reproductive technology, divorces, nonmarital child-rearing, adoption, and blended families.

Robert Crosnoe, a sociology professor at the University of Texas at Austin, said that many kids cycle through a variety of these family structures as they grow up, which means the regular introduction of new relatives. “There is more to keep track of, more to lose track of, and some family relationships may get lost in all of that churning,” Crosnoe told me. “You could see how a grandparent or two could lose visibility.” (He noted that while one-third seems high, he expects the actual proportion to be “not negligible.”)

Molly Fox, an anthropologist at UCLA, brought up several other demographic trends that could help explain the survey finding. First, she mentioned “immigration patterns to the U.S. over the past 50 years, as the geographic and linguistic separation of grandparents and grandchildren could fracture intergenerational family connections.” Another: “Diminishing family sizes in the U.S., such as having few siblings or few aunts and uncles compared to previous generations, could mean there are fewer sources for a person to call upon when trying to reconstruct the names of relatives in previous generations.”

Fox also wondered “how the ability to name your grandparents relates to them being alive during your lifetime, and perhaps events like WWII or the Vietnam War that resulted in a surge of early-adult deaths in the U.S. could have diminished the life span overlap of grandparents and grandchildren.”

Crosnoe also raised the question of how much grandparents’ lifespans overlap with their grandchildren’s, and provided some historical context. “Grandparenthood is sort of a modern invention, as for most of our history grandparents were dead before kids were born or got old enough to know them,” he said. “Declining mortality changed that and led to this modern phenomenon that kids tend to know their grandparents.”

“100 years ago,” he went on, “mortality would be the answer if you said a large chunk of grandkids could not name their grandparents (and probably immigration too).” Nowadays, happily (for the most part), there are a bunch of other, likelier explanations.

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