The internet has been "transformational" to the way we have relationships, says Pepper Schwartz, a professor of sociology at the University of Washington who studies dating.
Who hasn't read about how millennials are less religious, have fewer kids and, despite the popularity of Tinder and the less formal dating culture it's helped introduce, may even be having less sex?
So as time passes and people move around, the traditional pools from which you'd normally find a partner pretty much disappear, Schwartz said.
That leaves today's relationship seeker with few options other than to look online.
If you wanted to date only people who like Star Trek, normally you'd have to weed through several p'tahks before finding someone to join your crew, as it were.
Now there's a site for pretty Star Trek fans, as well as sites for vampire enthusiasts, gamers and even devotees to the writings of Ayn Rand.