Newborn baby girl Wattalage Muthumani, who was born at the Castel Street Maternity Hospital, is the “seven billionth” in the world. The milestone was marked as part of the U.N.'s seven billion global population projection. The world's population was said to reach seven billion on October 31, 2011, according to projections by the United Nations Population Fund, which says this global milestone presents both an opportunity and a challenge for the planet. Pix by Pradeep Dilruckshana