Another decade. Another high-school reunion. Why, despite the initial rolling of the eyeballs, do we choose to meet old flames, rediscover friends, dance badly to dated songs and most likely drink too much at a home-town bar or hotel? Why make the effort, when we have Facebook to see who’s gained weight or gone bald? Farah Stockman asked herself why she returned to East Lansing for her 20th year high school reunion. Being a Boston Globe columnist, her inquiry led to her to a mathematical ecologist and the question of why our hometowns keep calling us back.