"Conscientious people do a lot of things," Martin said. "They are more likely to gravitate into stable marriages. They are more likely to be in stable jobs that they are happy and passionate about. We know that both of these things are very important. Their social ties tend to be good. They are not the hardcore drinkers. Probably today, they would not smoke at all. It's that sort of pattern that encompasses a whole kind of specific behaviors that they do."
Identical twins are uncommon, but identical twins who live to be 100 are exceedingly rare, which is what makes Inez Harries and Venice Shaw so special.
Born 15 minutes apart on Jan. 15, 1911, the two sisters said they had been doing everything in sync since then, including celebrating their 100th birthdays together last month in California's San Fernando Valley.
Harries and Shaw were not part of Friedman and Martin's study, but they do fit several criteria of the authors' "conscientious" personality pattern. Although they are both divorced, each held jobs they loved for several years -- Harries worked for Lockheed Aircraft for 27 years and Shaw worked as a supervisor for 12 years in a plastics injection plant.
Both said they had stayed connected to people through their families and church.
"We were always close," they chimed in unison.
The twins also picked up hobbies and ate well -- all without worrying too much.
"Life goes on," Harries said. "No matter what happens you have to accept it and make the best of it."