High schools across Maine are celebrating the Class of 2015 this month, but the graduating class of North Yarmouth Academy has a special distinction: Within the top 10-ranked students, there are two sets of twins.

Marina and Olivia Stam are identical twins, as are Abbie and Tess Hinchman. Identical twins are the result of one fertilized egg splitting in half and occur about once in every 285 births. And that makes NYA’s high-achieving pair of twins a striking coincidence – and one that suggests there might be some academic advantage to having an identical double.

Tess, however, said that this was not her experience.

“I don’t really think it makes a difference for us,” she said. “We’re not … competitive with each other. I think our family has always just fostered a love of learning in us.”

“I think the one advantage is that I’ve never been without a study partner,” added Abbie wryly.

The Stam twins likewise did not believe it made an enormous difference, although the similarities in their academic records were striking.

“We’ve had the same exact schedule, same exact classes, every year,” said Olivia. “We have the same interests: We’re both more humanities-oriented. We both have been taking French since middle school, and we both love that.”

“One year we had the same GPA down to the second decimal place,” continued Marina. “We’re really close academically, but we’re not competitive with each other.”

The Stams and Hinchmans are the only twins in the class of 48 seniors at NYA. The Hinchmans live in West Bath and the Stams live in Cumberland. All of the top 10 students in the class are girls.

Both sets of siblings look very much alike, but their mannerisms are more similar still: They have near-identical speaking tones, bear themselves in the same way, and often finish the other’s sentences.

All four students are headed to different colleges: Marina to Bowdoin College, Olivia to Emory University, Tess to Tufts University and Abbie to Middlebury College. They said this will be a difficult experience at first.

“I think we’re nervous – we’ve never been apart for more than three days,” said Tess. “It’s going to be difficult for sure, but I think it’s also exciting.”

“When you’re a set of twins, you have an identity as ‘the twins,'” remarked Marina. “It’ll be nice just to be ourselves ….”

Clearly they all take pains to find their own niche.

Olivia is a first-chair flautist in the all-state orchestra, while Marina got into the top All-Conference Tennis Team this year. Tess volunteers four days a week tutoring young students, while Abbie was on a committee that last year raised $20,000 for a Guatemalan school.

They maintain that the negatives of having a twin are far outweighed by the positives.

“I think I’m really lucky – I’ve got to grow up with my best friend,” said Tess. “Abbie and I have never fought, and I’ve never had the concept of what it’s like to be lonely. I’ve always got someone in my corner, which is amazing.”

“The flip side of that is that when you’re a twin, your whole identity can be as a twin,” added Abbie. “You get pigeonholed. Either you’re the ‘smart twin’ or the ‘athletic twin’ or the ‘musical twin,’ and it’s not as clear-cut as that.”

Despite the long odds of having two sets of twins in the top 10 students, there is plenty of scientific evidence that there is more at work than coincidence or sibling rivalry. Studies into identical twins form a key part of the nature vs. nurture debate, and some of the results are arresting. In 1979, psychologist Thomas Bouchard investigated twins Jim Springer and Jim Lewis, separated at birth and reunited at the age of 39. He found that both had married and divorced a woman named Linda, before getting married again to a woman called Betty. One had named his son James Alan, the other had named his son James Allan, and both had had dogs called Toy. In addition, both had the same job, smoked the same cigarettes and drank the same beer.

The NYA twins are not quite as similar, but the Stams have a joke that “people tell us apart by our earrings.”

Heading to different colleges and being apart is “definitely bittersweet,” says Abbie.