Evolution directly challenges the idea of a creator God which is why so many religions reject it. Understanding how natural selection works – how it produces design without foresight – is the best way to undermine that idea.

Using evolutionary arguments can make believers angry or refuse to listen. I have had Christians and Muslims walk out of a lecture when I mentioned evolution. Their religions seem to include such meme-tricks as, ‘If you hear something that God disapproves of, don’t listen,’ or ‘Claim to be offended, and you can avoid new ideas’.

One way to get through is to explain how evolution actually works, though this is not as easy as it sounds. Many intelligent and well-educated undergraduates do not understand natural selection – or, if they do, they cannot explain it clearly enough when asked to. Darwin’s brilliant insight sounds simple but is so counter-intuitive that our minds tend to throw it off.

Once, stuck in a long airport line, I got chatting to an American Baptist preacher. He believed that God created each of us in his image and that evolution could not be true because a human being, with eyes and ears and intelligence could never evolve just by chance. So I explained why evolution is not chance.

The basic argument, as Darwin saw, entails three steps: If individuals vary; if most of the variants die; and if the few survivors pass on whatever helped them survive, then their offspring must be better adapted to their environment than they were. In other words, it’s inevitable. This sounds too abstract, so I held up my passport and said, 'Suppose we made ten copies of this passport, some with stronger or weaker covers, different colors, or more or fewer pages, and see how they perform. Then we throw nine away, copy and vary the best one ten times, and keep on doing that. What do you think will happen?’ He could see that better passports would appear rather quickly. I said that’s selection by us, but nature selects in just the same way. Imagine trees in a desert; those that need a lot of water die and only the drought tolerant ones have offspring. Imagine mice evading cats. Only the fastest runners survive to have babies who, like their parents, run faster and so on through the generations.

I saw the look on his face and knew he had got it. I have no idea what happened to him next but I know he had started thinking. Some people, having understood the inevitability of this mindless design process, find a way to reject it again. But lots can never go back to claiming that evolution is false and God made us. It is not argument but understanding how evolution works that makes the difference. —Susan Blackmore