The Number One girls’ name of the decade so far is Emily, with about 190,000 babies receiving that name since 2000.  And the top boys’ name is Jacob, given to nearly 229,000 boys this decade.

But there are other names that are given to more than twice as many babies as those Number One names.  Not many parents realize that the names they’re choosing carry this huge degree of popularity.  No states or government agencies track these names or alert people to what vast numbers of children receive them.

Why not?  Because they’re not a single name but a meganame, or a cluster of names, if you like.  These are names that are closely related in form and spelling, with lots of overlaps that sound exactly alike.  There are many examples in modern U.S. baby names – including to some extent Jacob and Emily themselves – but let’s focus on three of the most notorious.

For boys, the premier meganame might be thought of as the Aden cluster.  It includes the following names, arranged so that the relationships are most obvious:

ADEN
AIDEN
AIDAN
AYDEN
BRAYDEN
BRADEN
BRADY
CADE
CADEN
CAIDEN
CAYDEN
KADEN
KAIDEN
KAYDEN
HAYDEN
JAYDEN
JADEN
JAIDEN
JAYLEN
JALEN

There are undoubtedly more variations and spellings that might be included here – we didn’t diverge to Adrian or Zayden, for example – but taken together these names were given to about 480,000 baby boys in the 2000s, more than twice as many as received the name Jacob.

Of course, Brady and Jaylen feel fairly different – but Aden, Braden, and Jaden don’t, and Caden, Kaden and bros sound exactly alike.  Unsuspecting parents, especially those who haven’t been around kids much since they moved up to middle school themselves, might hear a name like Hayden or Aiden and think, wow, that’s really unique.  I want a special, modern, stand-out name for my son, not something everybody uses, like Jacob or Michael or Matthew.

And then they end up with a name that’s twice as common as any of those popular individual names.

For girls, let’s look at the meganame we might call Aylee (or Ayla or Kyla).  It’s far-ranging, and while you might not agree that every name below should be included in the cluster, there are many we left out.  This name cluster embraces:

BAILEY
BAYLEE
HAYLEE
HALEY
HAILEY
CALLIE
KAILEY
KAYLEE
KAYLEIGH
KAELYN
KAYLA
JAYLA
SHAYLA
MAKAYLA
MIKAYLA
KYLA
SKYLA
SKYLAR
SKYLER
KYLIE
KYLEE
RYLEE
RYLEIGH

Nearly 540,000 girls received these names this decade, compared with fewer than 200,000 who were named Emily.  And again, there are many more variations that might be lumped in with this group.

Another megapopular name that crosses gender lines is the Alex cluster, which accounts for nearly half a million baby boys and girls born this decade.  The names we’ve tallied in this cluster are:

ALEXANDRA
ALEXANDER
ALEX (boys)
ALEXA
ALEXIA
ALEXIS (both genders)
ALEXUS (girls)
LEXI
LEXIE
ALESSANDRA
ALEJANDRA
ALEXANDRIA
ALEJANDRO
ALEXANDRO
ALEXZANDER

The lesson: Alex might be a solid, attractive name that works equally well for boys and girls.  What it’s not is distinctive.

If you end up deciding you love Hayden or Hayley or Alexa anyway, go right ahead and choose them.   Just be aware that any name that’s got lots of close relatives is bound to feel far trendier than you’d guess by gauging the popularity of that name alone.

Thanks to our wonderful intern Danielle Miksza for her help with the research and math for this post.

You’ve probably noticed that Aiden is now way more popular than the original Irish Aidan.  And also that Zoey is catching up with Zoe, while other names like Isiah, Kaleb, Camryn and Sienna are either ahead of or breathing down the necks of their conventionally spelled cousins.  Sometimes the reasons for these changes are clear-cut, sometimes it’s just something in the ether.

Not that this is a new thing.  I remember the first time that someone asked me to spell my first name.  “Huh?”  “Well, is it Linda with an ‘i’ or Lynda with a ‘y’?  Without my really noticing, Lynda had become a spelling alternative in the wake of  the popularity of Lynn.  Something similar has happened with Aidan/Aiden.  When the epidemic of rhyming ‘en’-ending names erupted–Jaden, Braden, Caden et al–it was a logical development to make Aiden a legitimate member of that family.  And when ‘K’-beginning boys’ names became a rage, Kaleb began pursuing Caleb up the list.

The case of Zoe/Zooey is a little different, as the spike of the latter version can be pretty much traced to a single phenomenon–’Zoey101′–the Emmy-nominated teen sitcom starring (now teen mom) Jamie Lynn Spears, which appeared on Nickelodeon in 2005.  And the publicity surrounding Jamie Lynn’s big sister Britney’s second son helped spread that spelling of Brayden.  The rise of the British actress Sienna Miller spurred the spelling change of the Italian town of Siena, actress Jorja Fox legitimized the phonetic spelling of Georgia, and Gossip Girl hottie Chace (originally his middle name) Crawford has the spelling of his name chasing Chase.

In terms of image, rather than spelling, Scarlett Johansson challenged the long-term connection of her name to Gone With the Wind spitfire Scarlett O’Hara, just as the charms of Jude Law have managed to erase the age-old associations of his name to Judas.

More recently we’ve seen a couple of starbabies who might have some influence on the future spellings of names: Brooke Shield’s Grier (rather than Greer) and Angie Harmon’s Emery (rather than Emory).

Can you think of any others?

We’re often asked to talk about and predict names that are on their way up, but recently someone posed the reverse question, about names that have peaked and are trending downwards.  So here are a few thoughts on some categories of names that have gone from cool to hot to lukewarm, and their possible replacements.

WESTERN PLACE NAMES: Adios to cowboys and girls Dakota, Montana and Sierra, hello to more distant and exotic locales such as Rio, Vienna, Geneva, Sahara, Peru, Kenya

JADEN & CO: Even if it hasn’t quite happened yet, parents are bound to rebel against the megapopularity of all the nouveau Aidan siblings–Jayden, Caden, Cayden, Brayden, Kaden et al–and go back to  the original (now spelled) Aiden, which is rising in popularity all the time.

BIBLICAL GIRLS’ NAMES: Rebecca, Rachel, Hannah  and Sarah may be eternal classics, but many parents feel they have been way overused during the past few decades, and are seeking out  less common examples in the Good Book–Dinah?  Jael?  Salome?  Tamar?  Michal, anyone?–or choosing virtue names like Honor and Verity instead.  Biblical boys’ names, on the other hand, continue to thrive, with Jacob holding fast at Number One.

PREPPY SURNAMES: Upscale nineties favorites, such as the seriously striving Parkers and Porters, Carsons and Carters, seem to have lost their relevence in this changed economy, replaced by livelier, cheerier, unpretentious Irish family names like Sullivan, Brady, Reagan, Riley and Rafferty.  For what it’s worth, though, Cash is on the rise.