“You will probably not feel at home here unless anti-ableism, anti-ageism, anti-classism, anti-racism, consent, trans-positivity and queer-positivity, etc., are very important to you,” the ad read.

Image HOME WORK Members of a fledgling collective get to know each other in their new house in Brooklyn. Credit... Michael Nagle for The New York Times

Anti-ableism?

Ms. Feigelson, who works as a political organizer and volunteer, explained: “It means against the oppression of those who are physically or mentally disabled, and extends to language. Like you wouldn’t use the word ‘lame.’ ”

O.K., then. Ms. Feigelson was at home with some of her housemates, including Robin Markle, 23, who works at a community college teaching seniors computer skills, and Gauge, 30, who is transitioning from he to she and works in an S&M store, and also declined to give a last name. (“My family has no idea where I am  or if I’m even alive  and I’d like to keep it that way,” she said.) They were passing the phone around the afternoon before the G20 meeting in Pittsburgh, where a few of them were planning a trip, intending to protest, Ms. Markle said.

Ms. Feigelson explained that they were being “super-selective,” because an activist house, which is what she hopes theirs will be, she said, “can create tension.”

But were their hopes too high? Their criteria too stringent?

Helen Fisher, a biological anthropologist at Rutgers University and a relationship expert (she is the scientific adviser to Chemistry.com, a spinoff of the dating site Match.com), took a gander at a few of the ads, including the ones written by Ms. Berger and Ms. Hazard and the gang in Philadelphia.

The idealized, small-scale communities they described reminded her of the hunting and gathering bands of pre-history. So she was a bit concerned that their creators didn’t seem to be searching for individuals with different skill sets. Dr. Fisher, whose new book, “Why Him? Why Her?” explores the neurochemistry of gender differences, concluded that the ad writers were by and large “estrogen-expressives, or what I call Negotiators,” which she defined as “compassionate, verbal and emotive,” as well as “Explorers, meaning those expressive of the dopamine system, or people who are energetic, creative, politically liberal.”

She also noted that they all seemed to crave roommates who shared their values, which, she pointed out, “is how many relationships are built  it’s probably the right the thing to do. You don’t want to come home and spend your evening fighting with someone over health care. You want someone who agrees with you.”