SHELBYVILLE, Ind. (AP) — Maybe it was a lifetime of chores on the family farm that accounts for Edna Parker's long life. Or maybe just good genes explain why the world's oldest known person will turn 115 on Sunday, defying staggering odds.

Scientists who study longevity hope Parker and others who live to 110 or beyond — they're called supercentenarians — can help solve the mystery of extreme longevity.

"We don't know why she's lived so long," said Don Parker, her 59-year-old grandson. "But she's never been a worrier and she's always been a thin person, so maybe that has something to do with it."

On Friday, Edna Parker laughed and smiled as relatives and guests released 115 balloons into sunny skies outside her nursing home. Dressed in pearls, a blue and white polka dot dress and new white shoes, she clutched a red rose during the festivities.

Two years ago, researchers from the New England Centenarian Study at Boston University took a blood sample from Parker for the group's DNA database of supercentenarians.

Her DNA is now preserved with samples of about 100 other people who made the 110-year milestone and whose genes are being analyzed, said Dr. Tom Perls, an aging specialist who directs the project.

"They're really our best bet for finding the elusive Holy Grail of our field — which are these longevity-enabling genes," he said.

Only 75 living people — 64 women and 11 men — are 110 or older, according to the Gerontology Research Group of Inglewood, Calif., which verifies reports of extreme ages.

Parker, who was born April 20, 1893, was recognized by Guinness World Records as the oldest of that group last August after the death of a Japanese woman four months her senior.

A widow since her husband, Earl, died in 1938 of a heart attack, Parker lived alone in their farmhouse until age 100, when she moved into her son Clifford's home. She cheated death a few months later.

One winter night, Clifford and his wife returned home from a high school basketball game to find her missing. Don, their son, says he discovered his grandmother in the snowy darkness near the farm's apple orchard. He scooped up her rigid body and rushed back to the house.

"She was stiff as a 2-by-4. We really thought that was the end of her," he said.

But Parker recovered fully, suffering only frostbitten fingertips.

Fifteen years later, her room at the Heritage House Convalescent Center in Shelbyville, Ind., about 25 miles southeast of Indianapolis, is adorned with teddy bears and photos of her five grandchildren, 13 great-grandchildren and 13 great-great grandchildren. She's outlived her two sons, Clifford and Earl Jr.

During a visit this week, Parker was captivated by a new album of photos and documents from her life that Don's wife, Charlene, had assembled.

"That's the boys," she said hoarsely, tapping a photo of her two late sons in their youth. "Clifford and Junior."

Parker's granddaughter, Beverly Curnutt of Midland, Mich., previously told the Midland Daily News that her grandmother has led a life free of illness and has a gentle personality.

"She was an even-keeled person. She did not get upset easily," Curnutt said. "I never heard her raise her voice. She was very gracious, a kindhearted person, easy to talk with."

Her two sisters also are deceased. Georgia lived to be 99, while her sister Opal was 88 when she died.

Parker's long-lived sisters are typical of other centenarians, according to Dr. Nir Barzilai, director of the Albert Einstein College of Medicine's Institute for Aging Research in New York. Nearly all of them have a sister, mother or other relative who lived a long life, he said.

"Longevity is in the family history," Barzilai said.

He and other scientists have found several genetic mutations in centenarians that may play a role in either slowing the aging process or boosting resistance to age-related diseases.

Perls said the secret to a long life is now believed to be a mix of genetics and environmental factors such as health habits. He said his research on about 1,500 centenarians hints at another factor that may protect people from illnesses such as heart attacks and stroke — they appear not to dwell on stressful events.

"They seem to manage their stress better than the rest of us," he said.

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On the Net:

New England Centenarian Study: http://www.bumc.bu.edu/centenarian