Like other fresh food, fresh pears will heal 10 Hit Points, while providing no radiation. Fresh pears are the least available of the fresh foods, right behind fresh carrots.
Fresh pears and other fresh vegetables available in the Rivet City Science Lab are the direct result of the current Rivet City science project. There is a random bit of speech that may be told to the player from Janice Kaplinski that explains that they are the result of the work that is being undertaken in the lab.
The scientists at Rivet City have a large stock of fresh fruit and vegetables, and will say, "Be careful, that stuff is worth more than you" or "Don't touch the vegetables, they're fragile."