Of all the ideas that shape how natural history is perceived, none have been more influential than Charles Darwin's theory of evolution. The story, repeated again and again, is of the struggle for existence and how the fittest will survive to pass their characteristics to the next generation.
This theory is so widely accepted it has been almost forgotten that 150 years ago it constituted a revolution and unprecedented challenge to the orthodoxy that everything was designed by God. Many dismissed The Origin Of Species when it was published. 'Darwin would have been better off writing a book about pigeon-breeding,' wrote one reviewer.
In The Origin Of Species: An Illustrated Guide (Pearl, 8.30pm) Sir David Attenborough revisits Darwin's book and shows the key steps in what has become a virtually irrefutable argument.
Adaptability in the struggle for existence is demonstrated in another BBC programme, Uninvited Guests (Pearl, 9.05pm). This amusing film shows what will happen to your house if you abandon it. The natural world takes over, successfully adapting itself to all you leave behind. Slugs help themselves to remnant beer, lice chew up books and mouse populations explode.
Darwin's theories get another demonstration in 20/20 (Pearl, 8pm). Cynthia McFadden meets Chris Langan, a man who has an extremely rare and high IQ of 195. Only one in every 100 million enjoy such brain power. But Langan's experience suggests that this is unlikely to become a dominant human characteristic. His IQ has not resulted in business or monetary fitness, as important today as any physical characteristic in determining the success of our species.
The Origin Of Species provided the foundation for the unprecedented questioning of religion. Indirectly, it has given rise to many ideas that have tried to complement Darwin's world view with a new science-based spirituality. Some such religions are featured in the second and final part of In The Name Of God (World, 10pm).
Followers who have turned their backs on various cults describe the power the leaders assumed over their followers, their huge personal ambitions for this or subsequent worlds and the mechanisms of their influence. Mao Zedong's former Red Guards will understand the psychology.
Ron L Hubbard, founder of the Church Of Scientology; Dr Luc Jouret, who led members of the Order Of The Solar Temple to their deaths; and the Branch Davidians' David Koresh are among those featured. Only the Buddhist cult of Sokka Gakkai, or the Society For The Creation Of Value, comes out almost unscathed, for not being overly demanding on its members' lives or pockets.
This documentary implies that most of the new cults will not pass the survival-of-the-fittest test. Some will become exceedingly rich and politically powerful organisations for a while; others will leave trails of tragedy.