Bonus feature. Richard Dawkins presents: The Lava Lizard's Tale, The Giant Tortoise's Tale, and The Sea Turtle's Tale.

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?

In the second programme Prof. Dawkins explains that Darwin's Theory of Evolution presented a disturbing truth: that humans are animals – the fifth ape. This forces us to question whether our morals and manners are just a veneer. He confronts an issue that even Darwin skirted around – the evolution of human beings – and asks 'what does it mean to be evolved'? And in world where religions attack Darwinism for excusing selfish or even barbaric behaviour, Dawkins is forced to enter Darwinism's heart of darkness.

Although natural selection is the driving force of our evolution Dawkins clarifies that this does not mean that society should be run on Darwinian lines. "As a scientist I'm thrilled by natural selection, but as a human being I abhor it as a principle for organising society."

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".

Dawkins travels between Kenya (the birthplace of not only Dawkins, but the human race), America and the UK to explore what evolution really means for humans and human society.

Starting out in Africa, he speaks to palaeontologist Richard Leakey who assures him that "we are closer to chimpanzees than a horse is to an ass". But Dawkins finds that many religions are nevertheless censoriously opposed to Darwin's Theory of Evolution. He cannot convince evangelical Bishop Bonifes Adoyo that man evolved from ape, and posits that many (fearfully) reject Darwinism as a goal-less, soul-less theory. If nature – often ruthlessly competitive – is the model for human society then surely we inhabit a 'dog eat dog' world.

Exploring this line of thought, Dawkins investigates the world of the entrepreneurial businessman and social Darwinism, examining whether there are parallels to be drawn between economic and biological systems. He also explores the way in which Darwinism has been abused by those who have associated it with the eugenics movement or those who manipulate it to justify racism and right wing politics. Finally, in examining both the 'caring' behaviours of human beings and animals, he examines how the moral code of human beings, and their displays of sensitivity and altruism, can be reconciled with the idea of the survival of the fittest.

In this final episode Dawkins examines why Darwin's theory remains one of the most controversial ideas in history.

As Darwin set out on the voyage on the Beagle he still believed that god created the world and everything in it. But the evidence he discovered - fossils, patterns of anatomical resemblance, startling similarities of embryos and domestic breeding - demonstrated the truth: that all life forms vary and that some are more likely to reproduce, passing variations on. His wife Emma, however, was deeply religious and Darwin never criticized religion in public but he believed that "science would bring about a gradual illumination of minds".

Today, Dawkins argues, science has the evidence to prove that evolution is true. Modern discovery of the DNA code which links all life has added to the mountain of evidence showing that evolution is a fact. So why, he wonders as he meets creationists in America, is opposition to evolution more aggressive than ever?

Dawkins is also concerned that back in the UK teaching evolution has become a hugely sensitive issue for science teachers: "This is multicultural Britain. And one of its fault lines runs straight through our children's classrooms. How do we reconcile scientific truth with the deeply held convictions that bind religious communities?"

Returning to the school he visited in episode one, Dawkins confronts the science teachers and challenges their view that they "can't get in to the business of knocking down kid's religions and the religions of families." "There really is", he says, "something special about scientific evidence. Science works; planes fly. Magic carpets and broomsticks don't. Gravity isn't a version of the truth; it is the truth. Anybody who doubts it is invited to jump out of a tenth floor window. Evolution too, is reality."

This equivocation, Dawkins says, began with the Church of England who, rather than attack Darwin, embraced him in a "comfortable relativist fudge". So he meets the Archbishop of Canterbury to ask how he reconciles Darwin and the laws of physics with the miracles described in the bible.

Finally, Dawkins travels to meet an old friend, Dan Dennett, who shares many of his own beliefs, to answer the question Darwin himself was confronted with: how can we find solace in a godless world?