David Attenborough narrates the story of song across the animal world, tracing how sound evolved as a way to attract mates, mark territory, and communicate over distance. This first part looks at the earliest and simplest forms of animal sound, from insects rubbing wings and legs together to the calls of frogs and early vertebrates, building toward the more elaborate songs of birds and mammals covered later in the series. Attenborough's narration links each example back to a practical problem: how does a creature make itself heard over a rival, or heard at all in dense forest or open water. The footage moves between field recordings of calling animals and close-up shots of the physical mechanisms producing the sound. As the opening chapter in a multi-part series, it lays out the biological groundwork before the later parts move into the complexity of birdsong and whale song.