In fact, other scientists who study very-long-lived people have failed to find a mitochondrial connection. Nir Barzilai, director of the Institute for Aging Research at Albert Einstein College of Medicine, is studying Ashkenazi Jews who are 95 and older. He published two papers on haplogroups that showed no association with aging. “The mitochondria hypothesis in aging is very important; it’s just the evidence hasn’t been good,” Barzilai says. He adds that he did find a peptide in mitochondria that seems to be associated with aging—a discovery that illustrates how complicated the genetic picture is. “Maybe it’s not as simple as haplogroups,” he says.
The overall role of genetics in successful aging remains controversial. Linda Fried, dean of Columbia University’s Mailman School of Public Health, points to a study of Swedish twins in the 1990s undertaken by the MacArthur Foundation, which popularized the term “successful aging.” “Only 30 percent of variability in physical function and 50 percent of variability in cognitive function were heritable,” she says. Genetics, therefore, “can’t explain everything.”
Scott agrees that his team’s finding is just a starting point. He hopes to replicate the experiment in non-Amish people of European descent, to determine whether the results can be generalized to other populations. He also plans to study the DNA of people who have haplogroup X, so he can better describe how the variant alters mitochondrial function.
Further studies, Scott adds, should take into account environment and lifestyle, as well. Amish men and women have healthy diets, strong religious beliefs, and livelihoods that revolve around farming, with little help from modern machinery. “They’re more physically active than most,” Scott says. “We need to try to get clues about how these factors influence mitochondria.”