Parents who used sperm or egg donors to conceive are increasingly going online to see if their children have any genetic half-siblings, said Nick Vincour in Reuters. And according to a new study in the journal Human Reproduction, they are not only finding them in spades—one parent found at least 55 other children from the same sperm donor—but also, surprisingly, often forming strong relationships with them “based on notions of family and kinship.”

Still, 56 offspring? said William Saletan in Slate. That’s nearing “Genghis Khan action”—the Mongolian emperor is said to have 16 million male descendants. It seems fair, so long as we're all “beating up on Nadya Suleman,” the octomom, to give some hard thought to “all the men who have been fathering carloads of kids without even knowing about it.”

Actually, finding the half-siblings has been largely positive for the parents and donor children in the study, said Hayley Mick in Canada’s Globe and Mail. Even if the initial reason for contacting the 9-year-old Donor Sibling Registry was to “feed curiosity or gather health information,” many of the 791 parents and some of their kids are creating “new forms of extended families.”

And just who's forming those relationships is the interesting part of the study, said Seattle University law professor Julie Shapiro in her blog, not the “sensational” talk of Genghis Khan and Suleman. For example, most of the parents who consult the registry are single moms or lesbian couples—having 55 donor siblings is one thing, but having both a dad and “some sort of ‘donor dad’” is apparently too much for many heterosexual couples.