While managing a McDonald’s in Somerville and taking a course in restaurant management at Bunker Hill Community College in 1991, David Davidson answered an ad in the Globe to manage the graduate dining facility at Harvard University. “I just kind of latched onto this environment versus the restaurant field,’’ he says. After a variety of roles at Harvard, he spent the last four years as executive director of dining at Yale University before returning this fall as managing director of Harvard University Dining Services. Davidson, who grew up in Peabody in a family of 12 children, credits his experiences helping with dinners at home in preparing him for his new role, overseeing meals for more than 6,500 undergraduate students.