Hello, “Liam.” Hello, “Emma.”

This month, Baby Center released its trends list of the most popular baby names of 2019—and those two topped the list. They’d been rising in the charts for some time, too. For years, “Noah” was in #1 name for boys, and it took a long climb for “Liam” to knock it off its perch. Similarly, “Sophia” had ruled the roost for girls before “Emma” took the #1 position. Meanwhile, if you look much further down the charts, you can see a bunch of newer, dark-horse names that are gradually gaining in popularity. The male names “Genesis,” “Saint,” and “Baker” have surged forward in recent years, and so have the female names “Dior” and “Adalee.” Maybe ten years from now, one of those will be top dog.

That’s how names go. They rise in popularity, enjoy a period of dominance, and then fall. “Emma” and “Liam” will be hot for a while, until suddenly … they’re not.

But why? What makes a name suddenly pop—and then die?

Social scientists and historians have been puzzling over this for decades, and the short-but-unsatisfying answer is that no-one truly knows. But there are some intriguing clues!

One obvious one is the influence of pop culture. Parents get name ideas from everything from their favorite celebrities to characters in bestselling books. Or even pop music: In her paper “Brandy, You’re a Fine Name: Popular Music and the Naming of Infant Girls from 1965-1985”, Michelle Napierski-Prancl wondered if there was any correlation between top songs and the names of female children. Indeed, there appeared to be: When Kool and the Gang’s song “Joanna” hit the Billboard Hot 100 List in 1984, the name Joanna shot up in popularity. The same thing happened to “Rosanna” after Toto’s song of that name in 1982. Even some more-unconventional names saw a surge in the wake of a hit song. The names “Candida,” “Windy,” and “Ariel” were so unpopular names for babies that they had never even cracked the top 1,000. But after songs with those names became hummable hits in the 60s and 70s, they all suddenly debuted on the top baby-name charts.

Success was fleeting, though. As Napierski-Prancl found, the popularity of the name generally faded soon after the song itself left the charts. “This ends up creating a cohort of women who share a name that is popular for only a short period of time,” she writes. “Today someone named Windy or Candida is likely to be thought of as having an unusual name.” What’s more, following the pop-culture-name-of-the-moment can leave parents later slightly regretting how they hopped on the bandwagon. A survey of British parents, Napierski-Prancl notes, found that 20% “no longer liked the name they picked for their child,” with one reason being they regretted picking a name that at the time seemed “cool or clever.”

That said, the power of pop music had its limits. Some names were sufficiently unusual even a cosmically popular song couldn’t nudge them into popularity. When “My Sharona” by The Knack topped the charts for six weeks in 1979 (a song inspired by the singer’s real-life girlfriend, “Sharona”), it still couldn’t tip that name into the top 1,000 female baby names. Nor could “Hey, Deanie” in 1978.

It’s not just pop music that affects naming, though. Any part of mass culture can trigger hot new names—including politics, as the historian Arthur Schlesinger noted in his 1941 paper “Patriotism Names The Baby”.

In the earliest days of the Puritans immigrating to America, Americans tended to pick Biblical names, like “Ichabod” and “Samuel”; later, they switched to “moral attributes” like “Faith,” “Mercy,” and “Standfast.” But in the late 18^th century, the American Revolution began filling newspapers with tales of rebels fighting for independence from Britain. So American parents began naming their children “George Washington,” “Thomas Jefferson,” “Washington Irving.” and “Martha Dandridge,” the maiden name of George Washington’s wife. As Schlesinger notes:

… as the quarrel with the mother country developed and increasingly fired the popular emotions, the people began to attest their devotion to the American cause at the baptismal font.

After General Richard Montgomery was killed in the 1775 Battle of Quebec, American parents swooned over the tale and, it appears, his name. One reverend in Connecticut not only named his new son Montgomery but during the baptism dressed the child in military blue, “with a black feather on his cap, and a mourning token.”

Politics can have even subtler effects on the naming of children, it turns out. A pair of psychologists noted the long-held stereotype of Western Americans being highly independent, and wondered if it had any effect on baby naming. Sure enough, they found that parents in Northwestern states like Montana, Washington, Oregon, Idaho and Wyoming were the least likely in the country to pick popular baby names. Meanwhile, another study discovered that some parents appear to use their child’s name as a marker of political partisanship. After Ronald Reagan became president in the 80s, the name “Reagan”—previously quite rare—surged in popularity, landing in the top 100 by 2012. Yet there was an interesting wrinkle: The Republican parents were more likely to pick the name if they lived in a district that was purple, and contained Democrats. Living in a solidly red district tended to decrease the chance of naming a child “Reagan.”

Why? Possibly, the academics hypothesized, because the Republican parents were using the child’s name as a signalling mechanism—a way to tout their conservative bona fides in a politically mixed neighborhood. “It is not simply being in a safely Republican area that triggers the choice of a partisan name,” they noted, “but being in a place where there are Democrats around to spur the partisan identity.”

(One limitation of all this research I’m discussing, by the way: It appears to be mainly, and likely completely, about cisgendered naming practices.)

One intriguing, nation-wide trend in baby names? They’ve gotten more diverse as time has gone on. Over the last 100 years, Americans have increasingly embraced novelty. They’ve become less likely to pick already-popular names, and more likely to mint entirely new ones.

Back in 1900, for example, 91% of all children of any gender were given a name from the top 1,000 most popular names. But a century later in 2000, only 75% of girls were given a name from the top 1,000 most-popular girl names, and that percentage had dropped for boys too, to 86%. In other words, more kids were getting names that would have been considered unusual or new. (And the trend is more prominent for girls than boys: Americans are more willing to experiment with new names for girls, it seems, than for boys.)

You can even see how the zeitgeist of the age affected American’s desire for novelty. As Matthew W. Hahn and Alexander Bentley found, the incidence of new, unusual names rose in the 20s, peaked around 1930, but then plummeted in the 40s and 50s. Then it shot up again in the 60s, before reversing and plummeting again in the late 70s. Why? If you wanted to engage in some armchair zeitgeist analysis, you could argue that this makes a crude sort of cultural sense: The “roaring 20s” and the 60s were both periods when significant subsets of the population treasured creative, rule-breaking behavior; the 50s and early 80s weren’t.

The highest level of creativity, though, is in modern African-American naming conventions, as several scholars and thinkers have documented. One 1995 analysis studied African-American names between 1916 and 1989, looking for the incidence of “unique” names—one given to a single child in the country. In 1920, 31% of African-American girls and 25% of African-American boys in Illinois had unique names, higher than the rates for White Americans, at around 24% and 22% respectively. The rates of unique names chosen by African-American parents remained fairly stable until the 1960s—when they began to climb, reaching as high as 60% for girls around 1980.

As Sandra L. West—coauthor of the Encylopedia of the Harlem Renaissance—notes, that ferment of new names corresponded with its own cultural shifts, including the 1960s growth of the Black Power movement and the rejection of names that were originally forced on African-American families during slavery. “Black parents want their children to have unique names of glittering value, names that may very well be the only thing that glitters in their complicated lives,” she writes. Or as the scholars Ayanna F. Brown and Janice Tuck Lively write, “Insofar as they represent the creativity of a people who are willing to counter the culture of naming in Western society, they too remind us that one’s first name is given to you by one’s loved ones, unlike one’s last name, which is inherited from a legacy of indentured servitude and psychological abuse.”

Beneath all the cultural shifts in names, it appears that some popularity is driven by sheer prosody. Parents all suddenly glom onto a name simply because, at that moment in time, it just sounds interesting.

In their paper “From Karen to Katie: Using Baby Names to Understand Cultural Evolution,” a team of researchers discovered that when a name suddenly becomes popular, it might be related to the phonemes of previous hit names. Think of it this way: Imagine that in the year 2000, some of the most popular names begin with a hard K sound—like “Carl” or “Katie”—while other popular names end with a N sound (like “Darren” and “Warren”). In the following years, parents are statistically more likely to prefer names that combine those sounds, like “Karen.” Or to put it another way, names evolve out of the sounds of previous names. “Names like Aiden should be more likely to become popular when names like Jayden have been popular recently,” as the scientists note.

Even news events, it seems, can trigger this effect. If a name suddenly dominates the headlines, we subconsciously absorb its prosody. For example, when Hurricane Katrina wrecked Florida and Louisiana in 2005, it prompted stories for weeks, even months. The sheer prominence of the name “Katrina” appears to have had an impact: In the following years, the occurrence of names that began with “K” jumped by 9%. Because expecting parents walked around with the hard “K” sound on their lips, it created a preference for that phoneme when time came to name their new baby.

However a name arrives, one thing is for sure: Most often, the kid is stuck with it for life. “It must be remembered that, from infancy on, our first names dog us even more faithfully than our shadows,” as Schlesinger quipped. “The latter attend [to] us only when the light is good; the former cling to us day and night.” One can hope the Liams and Emmas, twenty years from now, are satisfied with their parents’ choice.