I have taken some flack for allegedly being a genetic determinist. Regular reader Jack Perry has written a post on his blog, Cantanima, about his son. Jack was wondering if, as a parent, he can do anything about the way his eleven-year-old has decided not to believe in God. Was this, he wonders, all determined by genes?
Let me first lay down what the science appears to tell us. Many human traits have a heritability of roughly 50%. This includes personality, religious proclivity and political allegiance. Fifty percent means half – so about half of who you are is genetic. We know this because identical twins have identical genes and we can test them to find out how different they are from each other. We find they share about half their characteristics (actually, it is more complicated than that but works out to about 50% overall). Non-identical twins have about a 25% correlation to each other, as do siblings who are not twins and children to their parents. This is because we take half our genes from each of our parents. If you share half your genes with someone then you will have a quarter of your heritable traits in common with them.
I think most of us can live with our genes having a half share in ourselves. St Augustine identified this long ago and called the propensity we get from our genes to behave other than we would like ‘original sin’. He also realised it was inherited from our parents. Clever guy, St Augustine.
The shocking fact is not that we are half made from our genetic natures. It is rather than we can find no room for nurture. If genes are half the story, we naturally assume that the other half must be our upbringing and environment. The trouble is, we have no evidence for this at all.
Over the years, scientists have conducted loads of twin studies. They take identical twins who have been separated at birth. As adults, these twins have exactly the same amount in common with each other as when both twins have been brought up by their birth parents. In other studies, it has been found that an adopted child has nothing in common with their adopted parents but the usual 25% correlation to their birth parents, even if they have never met them. This seems to mean that parenting does not have an effect on the traits contributed to by our genes. And, if parenting has no effect, it is hard to believe other environmental factors do either. For instance, in Freakonomics we learn about work in the Chicago schools system, where places are allocated at random, shows no correlation between pupils’ performance and the school they go to, once schools reach certain minimum standards.
That leaves the 50% of ourselves, for which our genes do not appear to have responsibility, unexplained. Personally, I am quite pleased that we are left with this gap. If scientists had said we are half determined by our genes and half by our environment then there would be no room left for self determination. I would suggest that the other half is who we want to be. We do have the freedom to decide. As even Richard Dawkins admits on the last page of The Selfish Gene, we can defy our DNA. Jack may not be able to make his son more likely to return to God. Instead, it is the boy himself who will decide where he wants to go and what he wants to believe in. Again, the theologians of old were right and science has just caught up.
Click here to read the first chapter of God's Philosophers: How the Medieval World Laid the Foundations of Modern Science absolutely free.