The Social Security Administration’s annual list of the most popular American baby names, released Monday, included, for boys, Aiden, Jayden, and Brayden and, for girls, Mia, Leah, and Sophia (as well as Sofia). Do baby names that rhyme tend to become popular at the same time?

Yes, but only since the Industrial Revolution. Previously, baby names weren’t subject to fads. Americans tended to give their children family names, and John and Mary were invariably the most popular. Girls’ names became subject to changing fashions before boys’ names did, and trendy names often peaked at the same time as other similar-sounding names. In 1880 (the earliest year for which the Social Security Administration has baby-name records), girls’ names ending in “-ie” were popular: The top 50 included Minnie, Jennie, Hattie, Mattie, Annie, and Fannie, among other “-ie” names.

By the 1920s, parents had begun naming their sons according to trends, too. In 1920, John still topped the boys’ list, but names ending in “-ard” had also begun to catch on in droves: Edward, Richard, Howard, and Leonard all made the top 50 that year. Other rhymes and near-rhymes continued to cluster together on baby-name lists throughout the decades: Doris, Dolores, Phyllis, and Gladys caught on among parents of newborn daughters in the 1930s and 1940s, as did Evelyn, Marilyn, and Carolyn. At the same time among boys, “-berts” were born in droves: Robert was the No. 1 boy’s name in 1930, with Herbert and Albert not far behind. In 1940, Donald and Ronald were the ninth and 10th most popular boys’ names, while Larry and Jerry took the 13th and 14th spots, respectively.

The recent rise of Aiden and similar-sounding boys’ names appears to have more staying power than past male-name trends. Over a third of American baby boys now get names that end in N (which makes boys’ names ending in N as common as girls’ names ending in A). And many of those names follow the same sound pattern: a long A in the first syllable and a schwa (or unstressed vowel) in the second syllable. Think also of Jason, Mason, and Nathan. In general, long-vowel sounds followed by schwas have gained in popularity in recent years among boys and girls: Ava, Layla, Noah, and Liam (all top-15 names in 2011) follow this pattern.

It’s clear that vowel sounds are in vogue for both boys’ and girls’ names, but it’s hard to say exactly why. It’s likely that baby-name trends are cyclical and reactive, as parents avoid baby names that were popular among their generation and their parents’ generation. Consonant-rich names like Herbert and Gladys are out of style now, but it’s possible that they’ll experience a comeback once today’s Jaydens and Mias begin procreating and opt for baby names that sound different from their own.

Got a question about today’s news? Ask the Explainer.

Explainer thanks Laura Wattenberg of babynamewizard.com.

Video Explainer: How Long Did Early Humans Breast-Feed Their Young?

This video was produced from an original Explainer by Brian Palmer.

Want more questions answered? You can now watch video Explainers at Slate’s News Channel on YouTube.