For twins, it really is about how the cookie crumbles.

Sandra Meyer explained that when she and her twin sister were growing up, "if there was one Oreo in the cookie jar, you'd split it in half. In my husband's family, with him and a little brother, you'd snatch it from the other person."

Little wonder, Meyer said, that when twins marry non-twins, misunderstandings can arise. "I'll ask my husband, 'Why didn't you break that last cookie in half?' and he says, 'Why would I?'"

Meyer laughed as she told this story, but the underlying message is serious. Being a twin, she said, "is the closest human relationship imaginable."

More than 150 twins will be in the Twin Cities this weekend for the annual convention of the International Twins Association, based in Oklahoma. Actually, they're gathering in Bloomington, having already split the convention cookie between Minneapolis in 1962 and St. Paul in 1986.

The gathering is a social event, said Meyer, of Chanhassen, who is the association's president. For many twins, it's a time when they can be alone with their sibling, without other distractions -- so much so that organizers are instituting a "speed twinning" event, similar to speed dating, on Friday to spur some fresh interactions.

"Sometimes, you don't get out into the world when you have such a close relationship," Meyer said. "Spouses often say, 'We knew from the beginning that we were never going to be number one in their life.' That can be a hard thing to accept, but those who do get along just fine."

She mentioned the husband of a twin who, whenever he's shopping for, say, a bracelet for his wife, always buys a duplicate for her twin sister.

If there's a common misunderstanding that singletons have about twins and other multiples, it's that siblings aren't individuals. "We may look alike, and act alike, and sound like, but there are differences," Meyer said.

Twins have a strong association to the state through a study at the University of Minnesota in the 1970s and 1980s. The Minnesota Study of Twins Reared Apart came to the controversial conclusion that a child's personality is due more to the genes he or she gets when conceived than to how that child is reared. That threw cold water on the contention that nurture is more important than nature, or that family and environment are more influential than what one researcher called "the great lottery that takes place at conception."

The study, which ended in 2000, was part of a National Geographic cover story about twins earlier this year.

Most people can't help but find multiples fascinating. "People are wide-eyed when we go out," Meyer said of any city where the convention is held. Many twins will dress alike, if only to highlight their relationship to passers-by.

"If you're not a twin, the bond is hard to understand," she said. "And if you are a twin, it's hard to imagine that relationship not being there."

Meyer knows this, given that her twin sister died 23 years ago of an infection related to a bone marrow transplant for leukemia. Meyer now is active in the Twinless Twins Support Group.

"I still behave from the twin perspective, though," she said. "I just choose to live my life for two. I try to double my accomplishments while having twice the fun."

Kim Ode • 612-673-7185