Natural World is the longest-running nature documentary series on British television. 2008 marked the series' 25th anniversary under its present title, though its origins can be traced back to its predecessor The World About Us which began over 40 years ago. Natural World is broadcast on BBC Two in the autumn and spring seasons; currently, 14 episodes are commissioned by the BBC each year. Production duties are shared between its in-house Natural History Unit, independent UK production companies and leading wildlife filmmakers from around the world. All episodes are now shot in high definition, and more than 400 have been screened in its first 25 years. The current series editor is Steve Greenwood. The latest series of Natural World began transmission in July 2010 with a study of harpy eagles in the Orinoco rainforest. Other episodes in the series feature British butterflies, a family of sea otters in Monterey harbour and a tribute to elephant matriarch Echo.