It is a weekly one-hour program that consists of documentaries about various animals and ecosystems. The on-camera host of the first season was Donald Johanson, with voice-over narration by George Page. Starting with the 1983 season, George Page became both the on-camera host and the narrator until the series' 19th season in 2000. Since then, Academy Award winner F. Murray Abraham has frequently narrated episodes, as has ecologist Chris Morgan.