How do you get 50,000 followers on Tumblr?

Clarisa relayed me this interesting tib-bit from a classmate at Medill who has a Tumblr blog with over 50,000 followers. How did that happen?
As for my blog, the only "press" I got that I know of is from Tumblr itself. It all started around the time I hit the Chicago newsroom, because I started posting my science writing. I was highlighted on one of their Tumblr Tuesday posts last March. I can't remember exactly how they found me, but one of their tag curators (for Science) started following me, and then one of the biggest Tumblr bloggers (SoupSoup) started following me and reblogged a few things of mine -- in fact, maybe they found me through him? Not sure.... Anyway, the big jump really happened this June. 

I know a few of the Tumblr staff through my blog, and I met one of them when she came out to Chicago for a meetup. I got an email some time last Spring from her asking me to fill out a tiny little bio for something they were planning. I never heard a thing more until they launched the Spotlight, where I'm featured in the Writers category. This is where the bulk of the followers came from, because not only is it an easy place to find people to follow, it's also the first thing that comes up when you get the new Tumblr app (which launched for the iPhone in June). So that's the long story of it. Sorry if you didn't want all the details.