My evangelical son and me

My parents were Jewish, and religious in a conventional and social way. We celebrated Jewish holidays and I had a bar mitzvah and went to synagogue every Saturday till I was 15, at my mother's insistence. I was quite a religious child, saying prayers each night and asking God for help with problems such as trying to find something I had lost. It did not seem to help, so I gave it all up around 16 and have been an atheist ever since. There just did not seem to me to be any evidence for a God. This had a very unfortunate effect on my mother, who was almost destroyed when I did not get married in a synagogue - though at least my wife was Jewish.

We had four children and they were not given any religious instruction. Then my youngest son, Matthew, who had been through a difficult late adolescence, became a Christian. He was evangelised and joined a church that took the Bible literally. I was not upset by his beliefs, as long as they helped him, but the following incident reflects our relationship.

Matthew came to visit me at work. He was studying Hebrew at the time, the better to understand the Bible. He said he was envious of me, as I was so fortunate. Totally unused to receiving positive remarks from my children, I beamed, and asked what he envied. The reply was: "You are going to die soon, certainly before me." I was shocked. Why was this so desirable? It was because he was still unhappy and wanted to die so that he could go, as he strongly believed, to heaven. We discussed this and it was clear that his position was totally rational, but he could not, according to the religious rules, take his own life. I had to accept his position, albeit reluctantly, but related the incident to his sister Jessica. A week later I found a note from Matthew on my chair: "Jessica says you think you are going to heaven when you die. We need to talk!" Of course Jessica was mistaken, but Matthew needed to check.

We did indeed talk, and he pointed out the danger I was in by not being religious. Many of our discussions were about the origin of life and evolution, and he was frustrated that he could not persuade me of God's role. He also thought that turning to God would help me significantly when I was going through a depression. But I have never been attracted to a religious belief. This may be related to my being a scientist, though there are scientists who are religious - remember Newton. However, I have never tried to change my son's religious views, as they seemed to help him so much. Matthew went on to become a teacher and now even does stand-up comedy. He is no longer a member of a church and is less dogmatic about his beliefs, though he still prays and finds that God has given him support by reducing his anxieties.

Religious beliefs are complex and variable, and present a difficult problem when we consider how they originated, are acquired and modified. My suggestion is that they all had their origin in the evolution of causal beliefs, which in turn had its origins in tool use. Only human beings have a causal understanding of the physical world: if they saw the wind blowing a branch of a fruit tree so the fruit fell off, they would know that by shaking the branch they could get the fruit. Given this ability, it was natural for humans to ask "Why" questions about events that affected their lives, such as death and illness. As the mental ability that leads to causal beliefs evolved from our primate ancestors and is largely determined by our genes constructing the appropriate neural circuits, one must ask if religion is also partly in our genes. Religion may also be adaptive in evolution. Although the studies are tentative, there is evidence for an inverse relationship between pain intensity and religious beliefs and attendance. This is consistent with the findings that those within a religious community enjoy better mental health, possibly due to social support.

Religion may thus be rooted in our biology. There are even claims that link spiritual experience to the activity of specific regions of the brain. Evidence for a role of the temporal lobes in religious experience comes from epilepsy originating in these lobes: the visions of St Teresa may have been associated with epilepsy of this kind. Despite these tentative answers, however, there is still much to learn about religious belief, which will, in its different forms, persist indefinitely.

The writer's latest book is Six Impossible Things Before Breakfast: the evolutionary origins of belief (Faber & Faber, £14.99)