Known as ‘ Darwin’s Rottweiler’, Professor Richard Dawkins relishes controversy. In his new TV series he explains how religion is a form of abuse – and why God is man’s most destructive invention ++ Why do you believe in your God? Because he talks to you inside your head? The Yorkshire Ripper claimed his murders were ordered by Jesus.

Imagine, sang John Lennon, a world with no religion. Imagine no suicide bombers, no 9/11, no 7/7, no Crusades, no witch-hunts, no Gunpowder Plot, no Kashmir dispute, no Indian partition, no Israel/Palestine war, no Serb/Croat/Muslim massacres, no Northern Ireland “troubles”. Imagine no Taliban to blow up ancient statues, no public beheadings of blasphemers, no flogging of female skin for the crime of showing an inch of it. Imagine no persecutions of the Jews – no Jews to persecute indeed, for, without religious taboos against marrying out, the Diaspora would long ago have merged into Europe.

Hitler invoked “My feelings as a Christian” to justify his anti-Semitism, and he wrote in Mein Kampf: “I believe that I am acting in accordance with the will of the Almighty Creator: by defending myself against the Jew, I am fighting for the work of the Lord.” Nevertheless, most such atrocities are not directly motivated by religion. IRA gunmen didn’t kill Protestants (or vice versa) over disagreements about transubstantiation or such theological niceties. The motive was more likely to be tribal vengeance. One of “them” killed one of “us”. “They” drove “our” great-grandfathers out of ancestral lands. Grievances are economic and political, not religious; and vendettas stretch “unto the third and fourth generation of them that hate me”. Quoting Exodus reminds me, incidentally, that humanists prefer Gandhi’s version: “An eye for an eye make the whole world blind.”

But if tribal wars are not about religion, the fact that there are separate tribes at all frequently is. Some tribes may divide along racial or linguistic lines, but in Northern Ireland what else is there but religion? The same applies to Indo-Pakistan, Serbo-Croatia, and various regions of Indonesia and Africa. Religion is today’s most divisive label of group identity and hostility. If a social engineer set out to devise a system for perpetuating our most vicious enmities, he could find no better formula than sectarian education. The main point of faith schools is that the children of “our” tribe must be taught “their own” religion. Since the children of the other tribe are simultaneously being taught the rival religion with, of course, the rival version of the vendetta-riven history, the prognosis is all too predictable.

But what can it mean to speak of a child’s “own” religion? Imagine a world in which it was normal to speak of a Keynesian child, a Hayekian child, or a Marxist child. Or imagine a proposal to pour government money into separate primary schools for Labour children, Tory children and Lib Dem children. Everyone agrees that small children are too young to know whether they are Keynesian or Monetarist, Labour or Tory: too young to bear the burden of heavy parental labels. Why, then, is almost our entire society happy to privilege religion, and slap a lab like Catholic or Protestant, Muslim or Jew, on a tiny child? Isn’t that a form of mental child abuse?a I once made that poiint in a broadcast debate with a Roman Catholic spokeswoman. I’ve forgotten her name but I she was some kind of agony aunt, and a stalwart of the Today programme’s “Thought f the Day”. When I said that a primary school child was too young to know whether it was a CCatholic child, she bristled: “Just come and talk to some of the children in our local Catholic school! I can assure you they know very well that they are Catholic children.” I believe it. The Jesuit boast – “Give me the child for his first seven years, and I’ll give you the man”– is no less sinister for being familiar to the point of cliché.

But what if religion is true? Surely sectarian indoctrination wouldn’t be child abuse if it saved the child’s immortal soul? Despite the smug presumptuousness of that, I can almost sympathise, if you sincerely believe your religion is the absolute truth. Let me, then, be ambitious if not presumptuous, and try to shake your belief.

Why do you believe in your God? Because he talks to you inside your head? Alas, the Yorkshire Ripper’s murders were ordered by the perceived voice of Jesus inside his head. The human brain is a consummate hallucinator, and hallucinations are a poor basis for real world beliefs. Or perhaps you believe in God because life would be intolerable without him. That’s an even weaker argument. Lots of things are intolerable and it doesn’t make them untrue. It may be intolerable that you are starving, but you can’t eat a stone by believing – no matter how passionately and sincerely – that it is made of cheese.

By far the favourite reason for believing in God is the argument from improbability. Eyes and skeletons, hearts and nerve cells are too improbable to have come about by chance. Man-made machines are improbable too, and designed by engineers for a purpose. Surely any fool can see that eyes and kidneys, wings and blood corpuscles must also be designed for a purpose, by a master Engineer? Well, maybe any fool can see it, but let’s stop playing the fool and grow up. It is 146 years since Charles Darwin gave us what is arguably the cleverest idea ever to occur to a human mind. He demonstrated a beautiful, working process whereby natural forces, by gradual degrees and with no deliberate purpose, forge an elegant illusion of design, to almost limitless levels of complexity.

I have written books on the subject and obviously can’t repeat the whole argument in a short article. Let me give just two guidelines to understanding. First, the commonest fallacy about natural selection is that it is a theory of chance. If it were, it is entirely obvious that it couldn’t explain the illusion of design. But natural selection, properly understood, is the antithesis of chance. Second, it is often said that natural selection makes God unnecessary, but leaves his existence an open plausibility. I think we can do better than that. When you think it through, the argument from improbability, which traditionally is deployed in God’s favour, turns out to be the strongest argument against him.

The beauty of Darwinian evolution is that it explains the very improbable, by gradual degrees. It starts from primeval simplicity (relatively easy to understand) and works up, by plausibly small steps, to complex entities whose genesis, by any non-gradual process, would be too improbable for serious contemplation. Design is a real alternative, but only if the designer is himself the product of an escalatory process such as evolution by natural selection, either on this planet or elsewhere. There may be alien life forms so advanced that we would worship them as gods. But they too must ultimately be explained by gradual escalation. Gods that exist ab initio are ruled out by the argument from improbability, even more surely than are spontaneously erupting eyes or elbow joints.

Religion may not be the root of all evil, but it is a serious contender. Even so it could be justified, if only its claims were true. But they are undermined by science and reason. Imagine a world where nobody is intimidated against following reason, wherever it leads. “You may say I’m a dreamer. But I’m not the only one.”

Professor Richard Dawkins is the Chair of the Public Understanding of Science at Oxford University. The Root of All Evil?, Professor Dawkins’ series looking at religion, is on 9 and 16 January at 8pm on Channel 4 link