In the first part of the series, Richard Dawkins retraces Darwin's journey as a scientist. He re-examines the rich evidence of the natural world – iguanas on the Galapagos islands, giant fossilized sloths in the Americas and even pigeons back home in England – which opened Darwin's eyes to the extraordinary truth that all living things must be related and had evolved from a common ancestor.

Darwin knew his espousal of evolution would cause outrage, challenging, as it did, the prevailing religious view of the world and our place in it. But, as Dawkins explains, it was really his theory of natural selection that undermined the notion of a benevolent God who designed all creatures great and small. Returning to his own birthplace, Kenya, Dawkins considers the brutal realities of the struggle for existence for wild animals on the plains of Africa. Here, he argues, we see the ongoing process sex, suffering and death, that drives evolution onward as the fittest survive to reproduce and the weakest perish without offspring.

And humans are not immune to the nightmarish Darwinian process. Dawkins travels to the slums of Nairobi where hundreds die of AIDS each year. Here he meets prostitutes who seem to have acquired a genetic immunity to the HIV virus. This resistance, it seems, can be inherited and so, over time, will become more prevalent, shaping the community here. "This," Dawkins tells us, "is the unstoppable force of natural selection".

Finally Dawkins visits a state of the art laboratory in America where scientists can now compare the genetic code of all living things, finally vindicating Darwin's theories once and for all. "He showed us that the world is beautiful and inspiring without a God. He revealed to us the glory of life and revealed who we really are and where we've come from".

But back in Britain can Dawkins convince a year 11 science class that evolution is the truth? Fearing that "a few hours in the science lab is no substitute for a lifetime of religious indoctrination" he takes the teenagers to Dorset's Jurassic Coast to examine fossil evidence for themselves. But will this win over this skeptical audience?