It’s December 2013 and Toni Osborne is struggling, emotionally and financially. She’s five pence short of keeping her electricity on over Christmas.

As she heads out into the night to ask her local shopkeeper for help, a homeless man appears and asks for some change. This is Jack Richardson, and when she bursts into tears, it prompts him to give Toni his last five pence. This simple act of giving would alter both their lives in profound ways.

In this episode, Matthew Syed explores how the effects of a seemingly small moment of generosity can ripple outwards, with significant consequences. He considers where this impulse to give to other people comes from and why we go out of our way to help others, sometimes at a cost to ourselves.

With Felix Warneken, Professor of Psychology at the University of Michigan; Dr Michael Rees, kidney transplant surgeon and founder of the Alliance for Paired Kidney Donation; and psychologist Scott Kaufman.

Presenter: Matthew Syed Producer: Eliza Lomas Series Editor: Katherine Godfrey Sound Design and Mix: Rob Speight Theme music by Ioana Selaru A Novel production for BBC Radio 4