Of boys' names, by parents of girls, that is. (I'd wager than ours is the first generation to really care about "name-stealing" by family and friends)
Many parents who like "softer" names for boys, or more "modern" names, are understandably concerned about their favorite boys' names "turning girl". While I'm not convinced that teasing is a big issue for this generation--unisex names are more common than ever--I can understand the appeal of a gender-obvious name.
Tons of our current girls' names were originally boys', but since I've heard of elderly women named Billie, Freddie, George, etc., I have to wonder if giving girls masculine names (or masculine nicknames as full names) has really been jumping lately; or if we're just victims of the over-information effect, and it's really been going on for decades with most names not really "sticking" for girls. (and yes, if this seems familiar, it's because I did sort of do a similar post earlier).
So, I've gone through the Top 1000 SSA lists from 1890, 1920, 1950, 1980, and 2010 (approximately the past 5 generations); and counted up every name on the girls' side which was more common for boys at the time or within the prior 15 years (a bit arbitrary to be sure, but I needed some way to count names like Morgan, Avery, Leslie, etc., that suddenly sky-rocketed in less than a generation). I also added in any alternate spellings from the full SSA lists.
Some names were not included in this analysis because they were never widely used for boys in the past, despite being masculine in meaning: Madison, Addison, & Mackenzie, for example.
And yes, the 1890 and 1920 lists will be more prone to inaccuracy than the others (SSA registration was optional before 1937), but hopefully we'll still get a rough idea.
So, tallying it up--
1890: 66 names, 1.3% of girls. Most used: Willie, Ollie, Francis, Artie, Frankie
1920: 62 names, 1.3% of girls. Most used: Willie, Johnnie, Billie, Ollie, Francis
1950: 51 names, 1.3% of girls. Most used: Leslie, Bobbie, Jerry, Billie, Willie
1980: 43 names, 1.7% of girls. Most used: Ashley, Casey, Bobbie, Toni, Corey
2010: 31 names, 3.0% of girls. Most used: Riley, Avery, Jordyn, Jayden, Camryn
Holy crap! Honestly, I hadn't expected that big of a jump from 1980 to 2010. I also find it interesting how the number of boys' names used on girls decreased, even though the percentage of girls with boys' names increased overall.
A few interesting things:
--In the first 2 sets (1890 & 1920), almost all the names were the diminutives of boys' names, and almost always spelled ____ie.
--Nearly every "boys" name from 2010 had several spelling alternates, while only 3 did in 1890.
--Most of the boys' names used by girls over the years did not end up "going to the girls".
Out of the 155 boys' names that made it onto a girls' Top 1000 list, only 26 have become more popular for girls: Shirley (1890s), Meredith (1920s), Leslie, Lauren, Lynn (1940s), Dana, Kelly, Kim, Tracy (1950s), Ashley (1960s), Aubrey, Jamie, Kelsey, Lacy, Lindsay, Morgan (1970s), Blair, Sydney, Taylor (1980s), Avery, Kendall (1990s), Emerson, Emery, Quinn, Reese, Riley (2000s).
--The wider variety, but smaller percentage, of boys' names used on girls in earlier decades indicates to me that parents didn't do it because it was "cool" or "cute", but that it was done for more personal reasons, like perhaps honoring someone, or passing down a family surname. The fact that the more recent conversions became very popular, very fast, rather than over the course of decades, seems to support that.
--Rather than increasing, the overtaking of boys' names by girls seems to occur in random bursts; possibly slightly periodic. Of course, this doesn't take into account the names that "turned girl" prior to the late-1800s, like Vivian, Jocelyn, Beverly, Evelyn, and Esme.