If you have a faith, it is statistically overwhelmingly likely that it is the same faith as your parents and grandparents had. No doubt soaring cathedrals, stirring music, moving stories and parables, help a bit. But by far the most important variable determining your religion is the accident of birth. The convictions that you so passionately believe would have been a completely different, and largely contradictory, set of convictions, if only you had happened to be born in a different place.

The moral law is a reason to think of God as plausible - not just a God who sets the universe in motion but a God who cares about human beings, because we seem uniquely amongst creatures on the planet to have this far-developed sense of morality.

Science has eradicated smallpox, can immunise against most previously deadly viruses, can kill most previously deadly bacteria. Theology has done nothing but talk of pestilence as the wages of sin.

Such delusions of grandeur to think that a God with a hundred billion galaxies on his mind would give a tuppenny damn who you sleep with, or indeed whether you believe in him.

What you cannot have is a gene that sacrifices itself for the benefit of other genes. What you can have is a gene that makes organisms sacrifice themselves for other organisms under the influence of selfish genes.

Cheetah genes cooperate with cheetah genes but not with camel genes, and vice versa. This is not because cheetah genes, even in the most poetic sense, see any virtue in the preservation of the cheetah species. They are not working to save the cheetah from extinction like some molecular World Wildlife Fund.

Matthew and Luke handle the problem differently, by deciding that Jesus must have been born in Bethlehem after all. But they get him there by different routes.